1
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Marsh D. Rate constants for saturation-recovery EPR and ELDOR of 14N-Spin labels. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2023; 350:107414. [PMID: 36913743 DOI: 10.1016/j.jmr.2023.107414] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/01/2022] [Revised: 02/21/2023] [Accepted: 03/02/2023] [Indexed: 05/10/2023]
Abstract
Saturation-recovery (SR)-EPR can determine electron spin-lattice relaxation rates in liquids over a wide range of effective viscosity, making it especially useful for biophysical and biomedical applications. Here, I develop exact solutions for the SR-EPR and SR-ELDOR rate constants of 14N-nitroxyl spin labels as a function of rotational correlation time and spectrometer operating frequency. Explicit mechanisms for electron spin-lattice relaxation are: rotational modulation of the N-hyperfine and electron-Zeeman anisotropies (specifically including cross terms), spin-rotation interaction, and residual frequency-independent vibrational contributions from Raman processes and local modes. Cross relaxation from mutual electron and nuclear spin flips, and direct nitrogen nuclear spin-lattice relaxation, also must be included. Both the latter are further contributions from rotational modulation of the electron-nuclear dipolar interaction (END). All the conventional liquid-state mechanisms are defined fully by the spin-Hamiltonian parameters; only the vibrational contributions contain fitting parameters. This analysis gives a firm basis for interpreting SR (and inversion recovery) results in terms of additional, less standard mechanisms.
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Affiliation(s)
- Derek Marsh
- Max-Planck Institute for Multidisciplinary Sciences, 37070 Göttingen, Germany(1).
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2
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Subczynski WK, Widomska J. Spin-Lattice Relaxation Rates of Lipid Spin Labels as a Measure of Their Rotational Diffusion Rates in Lipid Bilayer Membranes. MEMBRANES 2022; 12:962. [PMID: 36295720 PMCID: PMC9612125 DOI: 10.3390/membranes12100962] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/08/2022] [Revised: 09/26/2022] [Accepted: 09/27/2022] [Indexed: 06/16/2023]
Abstract
The spin-lattice relaxation rate (T1-1) of lipid spin labels obtained from saturation recovery EPR measurements in deoxygenated membranes depends primarily on the rate of the rotational diffusion of the nitroxide moiety within the lipid bilayer. It has been shown that T1-1 also can be used as a qualitative convenient measure of membrane fluidity that reflects local membrane dynamics; however, the relation between T1-1 and rotational diffusion coefficients was not provided. In this study, using data previously presented for continuous wave and saturation recovery EPR measurements of phospholipid analog spin labels, one-palmitoyl-2-(n-doxylstearoyl)phosphatidylcholine in 1,2-dimyristoyl-sn-glycero-3-phosphorylcholine/cholesterol membranes, we show that measured T1-1 values are linear functions of rotational diffusion of spin labels. Thus, these linear relationships can be used to transfer T1-1 values into spin label rotational rates as a precise description of membrane fluidity. This linearity is independent through the wide range of conditions including lipid environment, depth in membrane, local hydrophobicity, and the anisotropy of rotational motion. Transferring the spin-lattice relaxation rates into the rotational diffusion coefficients makes the results obtained from saturation recovery EPR spin labeling easy to understand and readily comparable with other membrane fluidity data.
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Affiliation(s)
- Witold K. Subczynski
- Department of Biophysics, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA
| | - Justyna Widomska
- Department of Biophysics, Medical University of Lublin, Jaczewskiego 4, 20-400 Lublin, Poland
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Subczynski WK, Widomska J, Raguz M, Pasenkiewicz-Gierula M. Molecular oxygen as a probe molecule in EPR spin-labeling studies of membrane structure and dynamics. OXYGEN (BASEL, SWITZERLAND) 2022; 2:295-316. [PMID: 36852103 PMCID: PMC9965258 DOI: 10.3390/oxygen2030021] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Molecular oxygen (O2) is the perfect probe molecule for membrane studies carried out using the saturation recovery EPR technique. O2 is a small, paramagnetic, hydrophobic enough molecule that easily partitions into a membrane's different phases and domains. In membrane studies, the saturation recovery EPR method requires two paramagnetic probes: a lipid-analog nitroxide spin label and an oxygen molecule. The experimentally derived parameters of this method are the spin-lattice relaxation times (T 1s) of spin labels and rates of bimolecular collisions between O2 and the nitroxide fragment. Thanks to the long T 1 of lipid spin labels (from 1 to 10 μs), the approach is very sensitive to changes of the local (around the nitroxide fragment) O2 diffusion-concentration product. Small variations in the lipid packing affect O2 solubility and O2 diffusion, which can be detected by the shortening of T 1 of spin labels. Using O2 as a probe molecule and a different lipid spin label inserted into specific phases of the membrane and membrane domains allows data about the lateral arrangement of lipid membranes to be obtained. Moreover, using a lipid spin label with the nitroxide fragment attached to its head group or a hydrocarbon chain at different positions also enables data about molecular dynamics and structure at different membrane depths to be obtained. Thus, the method can be used to investigate not only the lateral organization of the membrane (i.e., the presence of membrane domains and phases), but also the depth-dependent membrane structure and dynamics, and, hence, the membrane properties in three dimensions.
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Affiliation(s)
- Witold K. Subczynski
- Department of Biophysics, Medical College on Wisconsin, Milwaukee, United States
| | - Justyna Widomska
- Department of Biophysics, Medical University of Lublin, Lublin, Poland
| | - Marija Raguz
- Department of Medical Physics and Biophysics, University of Split School of Medicine, Split, Croatia
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Subczynski WK, Raguz M, Widomska J. Multilamellar Liposomes as a Model for Biological Membranes: Saturation Recovery EPR Spin-Labeling Studies. MEMBRANES 2022; 12:657. [PMID: 35877860 PMCID: PMC9321980 DOI: 10.3390/membranes12070657] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/31/2022] [Revised: 06/22/2022] [Accepted: 06/23/2022] [Indexed: 11/23/2022]
Abstract
EPR spin labeling has been used extensively to study lipids in model membranes to understand their structures and dynamics in biological membranes. The lipid multilamellar liposomes, which are the most commonly used biological membrane model, were prepared using film deposition methods and investigated with the continuous wave EPR technique (T2-sensitive spin-labeling methods). These investigations provided knowledge about the orientation of lipids, their rotational and lateral diffusion, and their rate of flip-flop between bilayer leaflets, as well as profiles of membrane hydrophobicity, and are reviewed in many papers and book chapters. In the early 1980s, the saturation recovery EPR technique was introduced to membrane studies. Numerous T1-sensitive spin-label methods were developed to obtain detailed information about the three-dimensional dynamic membrane structure. T1-sensitive methods are advantageous over T2-sensitive methods because the T1 of spin labels (1-10 μs) is 10 to 1000 times longer than the T2, which allows for studies of membrane dynamics in a longer time-space scale. These investigations used multilamellar liposomes also prepared using the rapid solvent exchange method. Here, we review works in which saturation recovery EPR spin-labeling methods were applied to investigate the properties of multilamellar lipid liposomes, and we discuss their relationships to the properties of lipids in biological membranes.
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Affiliation(s)
| | - Marija Raguz
- Department of Medical Physics and Biophysics, University of Split School of Medicine, 21000 Split, Croatia
| | - Justyna Widomska
- Department of Biophysics, Medical University of Lublin, 20 093 Lublin, Poland;
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Subczynski WK, Widomska J, Stein N, Swartz HM. Factors determining barrier properties to oxygen transport across model and cell plasma membranes based on EPR spin-label oximetry. APPLIED MAGNETIC RESONANCE 2021; 52:1237-1260. [PMID: 36267674 PMCID: PMC9581439 DOI: 10.1007/s00723-021-01412-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/21/2021] [Revised: 07/23/2021] [Accepted: 08/04/2021] [Indexed: 06/01/2023]
Abstract
This review is motivated by the exciting new area of radiation therapy using a phenomenon termed FLASH in which oxygen is thought to have a central role. Well-established principles of radiation biology and physics suggest that if oxygen has a strong role, it should be the level at the DNA. The key aspect discussed is the rate of oxygen diffusion. If oxygen freely diffuses into cells and rapidly equilibrates, then measurements in the extracellular compartment would enable FLASH to be investigated using existing methodologies that can readily measure oxygen in the extracellular compartment. EPR spin-label oximetry allows evaluation of the oxygen permeability coefficient across lipid bilayer membranes. It is established that simple fluid phase lipid bilayers are not barriers to oxygen transport. However, further investigations indicate that many physical and chemical (compositional) factor can significantly decrease this permeation. In biological cell plasma membranes, the lipid bilayer forms the matrix in which integral membrane proteins are immersed, changing organization and properties of the lipid matrix. To evaluate oxygen permeability coefficients across these complex membranes, oxygen permeation across all membrane domains and components must be considered. In this review, we consider many of the factors that affect (decrease) oxygen permeation across cell plasma membranes. Finally, we address the question, can the plasma membrane of the cell form a barrier to the free diffusion of oxygen into the cell interior? If there is a barrier then this must be considered in the investigations of the role of oxygen in FLASH.
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Affiliation(s)
- Witold K. Subczynski
- Department of Biophysics, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA
| | - Justyna Widomska
- Department of Biophysics, Medical University of Lublin, Jaczewskiego 4, Lublin, Poland
| | - Natalia Stein
- Department of Biophysics, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA
| | - Harold M. Swartz
- Department of Radiology, The Geisel School of Medicine at Dartmouth, Lebanon, NH 03766, USA
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Stein N, Subczynski WK. Differences in the properties of porcine cortical and nuclear fiber cell plasma membranes revealed by saturation recovery EPR spin labeling measurements. Exp Eye Res 2021; 206:108536. [PMID: 33716012 DOI: 10.1016/j.exer.2021.108536] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2021] [Revised: 02/24/2021] [Accepted: 03/06/2021] [Indexed: 10/21/2022]
Abstract
Eye lens membranes are complex biological samples. They consist of a variety of lipids that form the lipid bilayer matrix, integral proteins embedded into the lipid bilayer, and peripheral proteins. This molecular diversity in membrane composition induces formation of lipid domains with particular physical properties that are responsible for the maintenance of proper membrane functions. These domains can be, and have been, effectively described in terms of the rotational diffusion of lipid spin labels and oxygen collision with spin labels using the saturation recovery (SR) electron paramagnetic resonance method and, now, using stretched exponential function for the analysis of SR signals. Here, we report the application of the stretched exponential function analysis of SR electron paramagnetic resonance signals coming from cholesterol analog, androstane spin label (ASL) in the lipid bilayer portion of intact fiber cell plasma membranes (IMs) isolated from the cortex and nucleus of porcine eye lenses. Further, we compare the properties of these IMs with model lens lipid membranes (LLMs) derived from the total lipids extracted from cortical and nuclear IMs. With this approach, the IM can be characterized by the continuous probability density distribution of the spin-lattice relaxation rates associated with the rotational diffusion of a spin label, and by the distribution of the oxygen transport parameter within the IM (i.e., the collision rate of molecular oxygen with the spin label). We found that the cortical and nuclear LLMs possess very different, albeit homogenous, spin lattice relaxation rates due to the rotational diffusion of ASL, indicating that the local rigidity around the spin label in nuclear LLMs is considerably greater than that in cortical LLMs. However, the oxygen transport parameter around the spin label is very similar and slightly heterogenous for LLMs from both sources. This heterogeneity was previously missed when distinct exponential analysis was used. The spin lattice relaxation rates due to either the rotational diffusion of ASL or the oxygen collision with the spin label in nuclear IMs have slower values and wider distributions compared with those of cortical IMs. From this evidence, we conclude that lipids in nuclear IMs are less fluid and more heterogeneous than those in cortical membranes. Additionally, a comparison of properties of IMs with corresponding LLMs, and lipid and protein composition analysis, allow us to conclude that the decreased lipid-to-protein ratio not only induces greater rigidity of nuclear IMs, but also creates domains with the considerably decreased and variable oxygen accessibility. The advantages and disadvantages of this method, as well as its use for the cluster analysis, are discussed.
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Affiliation(s)
- Natalia Stein
- Department of Biophysics, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI, 53226, USA.
| | - Witold K Subczynski
- Department of Biophysics, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI, 53226, USA.
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Mainali L, O’Brien WJ, Timsina R. Interaction of Alpha-Crystallin with Phospholipid Membranes. Curr Eye Res 2021; 46:185-194. [PMID: 32564617 PMCID: PMC7790885 DOI: 10.1080/02713683.2020.1786131] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2020] [Revised: 05/29/2020] [Accepted: 06/09/2020] [Indexed: 02/07/2023]
Abstract
Purpose/Aim: The amount of membrane-bound α-crystallin increases significantly with age and cataract formation, accompanied by a corresponding decline in the level of α-crystallin in the lens cytoplasm. The purpose of this research is to evaluate the binding affinity of α-crystallin to the phospholipid membranes as well as the physical properties of the membranes after α-crystallin binding. Materials and Methods: The continuous wave and saturation recovery electron paramagnetic resonance (EPR) methods were used to obtain the information about the binding affinity and the physical properties of the membrane. In this approach, the cholesterol analog spin label CSL was incorporated in the membrane and the binding of α-crystallin to the membrane was monitored by this spin label. Small uni-lamellar vesicles were prepared from 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) with 1% of CSL. The measured membrane properties included the mobility parameter, fluidity, and the oxygen transport parameter. Results: The binding affinity (Ka ) of α-crystallin with the POPC membrane was estimated to be 4.9 ± 2.4 µM-1. The profiles of mobility parameter showed that mobility parameter decreased with an increase in the binding of α-crystallin. The profiles of spin-lattice relaxation rate showed that the spin-lattice relaxation rate decreased with an increase in binding. These results show that the binding of α-crystallin makes the membrane more immobilized near the head group region of the phospholipids. Furthermore, the profiles of the oxygen transport parameter indicated that the oxygen transport parameter decreased with an increase of binding, indicating the binding of α-crystallin forms a barrier for the passage of non-polar molecules which supports the barrier hypothesis. Conclusions: The binding of α-crystallin to the membrane alters the physical properties of the membranes, and this plays a significant role in modulating the integrity of the membranes. EPR techniques are useful in studying α-crystallin membrane interactions.
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Affiliation(s)
- Laxman Mainali
- Department of Physics, Boise State University, Boise, Idaho, USA
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, Wisconsin 53226, USA
| | - William J. O’Brien
- Department of Ophthalmology and Visual Sciences, Medical College of Wisconsin, Milwaukee, WI, USA
| | - Raju Timsina
- Department of Physics, Boise State University, Boise, Idaho, USA
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Stein N, Subczynski WK. Oxygen Transport Parameter in Plasma Membrane of Eye Lens Fiber Cells by Saturation Recovery EPR. APPLIED MAGNETIC RESONANCE 2021; 52:61-80. [PMID: 33776217 PMCID: PMC7992188 DOI: 10.1007/s00723-020-01237-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/08/2020] [Revised: 07/24/2020] [Indexed: 06/02/2023]
Abstract
A probability distribution of rate constants contained within an exponential-like saturation recovery (SR) electron paramagnetic resonance signal can be constructed using stretched exponential function fitting parameters. Previously (Stein et al. Appl. Magn. Reson. 2019.), application of this method was limited to the case where only one relaxation process, namely spin-lattice relaxations due to the rotational diffusion of the spin labels in the intact eye-lens membranes, contributed to an exponential-like SR signal. These conditions were achieved for thoroughly deoxygenated samples. Here, the case is described where the second relaxation process, namely Heisenberg exchange between the spin label and molecular oxygen that occurs during bimolecular collisions, contributes to the decay of SR signals. We have further developed the theory for application of stretched exponential function to analyze SR signals involving these two processes. This new approach allows separation of stretched exponential parameters, namely characteristic stretched rates and heterogeneity parameters for both processes. Knowing these parameters allowed us to separately construct the probability distributions of spin-lattice relaxation rates determined by the rotational diffusion of spin labels and the distribution of relaxations induced strictly by collisions with molecular oxygen. The later distribution is determined by the distribution of oxygen diffusion concentration products within the membrane, which forms a sensitive new way to describe membrane fluidity and heterogeneity. This method was validated in silico and by fitting SR signals from spin-labeled intact nuclear fiber cell plasma membranes extracted from porcine eye lenses equilibrated with different fractions of air.
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Affiliation(s)
- N. Stein
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, USA
| | - W. K. Subczynski
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, USA
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Moore W, McPeak JE, Poncelet M, Driesschaert B, Eaton SS, Eaton GR. 13C isotope enrichment of the central trityl carbon decreases fluid solution electron spin relaxation times. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2020; 318:106797. [PMID: 32769018 PMCID: PMC7492462 DOI: 10.1016/j.jmr.2020.106797] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/11/2020] [Revised: 07/21/2020] [Accepted: 07/22/2020] [Indexed: 05/19/2023]
Abstract
Electron spin relaxation times for perdeuterated Finland trityl 99% enriched in 13C at the central carbon (13C1-dFT) were measured in phosphate buffered saline (pH = 7.2) (PBS) solution at X-band. The anisotropic 13C1 hyperfine (Ax = Ay = 18 ± 2, Az = 162 ± 1 MHz) and g values (2.0033, 2.0032, 2.00275) in a 9:1 trehalose:sucrose glass at 293 K and in 1:1 PBS:glycerol at 160 K were determined by simulation of spectra at X-band and Q-band. In PBS at room temperature the tumbling correlation time, τR, is 0.29 ± 0.02 ns. The linewidths are broadened by incomplete motional averaging of the hyperfine anisotropy and T2 is 0.13 ± 0.02 µs, which is shorter than the T2 ~ 3.8 µs for natural abundance dFT at low concentration in PBS. T1 for 13C1-dFT in deoxygenated PBS is 5.9 ± 0.5 µs, which is shorter than for natural abundance dFT in PBS (16 µs) but much longer than in air-saturated solution (0.48 ± 0.04 µs). The tumbling dependence of T1 in PBS, 3:1 PBS:glycerol (τR = 0.80 ± 0.05 ns, T1 = 9.7 ± 0.7 µs) and 1:1 PBS:glycerol (τR = 3.4 ± 0.3 ns, T1 = 12.0 ± 1.0 µs) was modeled with contributions to the relaxation predominantly from modulation of hyperfine anisotropy and a local mode. The 1/T1 rate for the 1% 12C1-dFT in the predominantly 13C labeled sample is about a factor of 6 more strongly concentration dependent than for natural abundance 12C1-trityl, which reflects the importance of Heisenberg exchange with molecules with different resonance frequencies and faster relaxation rates. In glassy matrices at 160 K, T1 and Tm for 13C1-dFT are in good agreement with previously reported values for 12C1-dFT consistent with the expectation that modulation of nuclear hyperfine does not contribute to electron spin relaxation in a rigid lattice.
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Affiliation(s)
- Whylder Moore
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80210, USA
| | - Joseph E McPeak
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80210, USA
| | - Martin Poncelet
- Department of Pharmaceutical Sciences, School of Pharmacy & In Vivo Multifunctional Magnetic Resonance Center, West Virginia University, Morgantown, WV 26506, USA
| | - Benoit Driesschaert
- Department of Pharmaceutical Sciences, School of Pharmacy & In Vivo Multifunctional Magnetic Resonance Center, West Virginia University, Morgantown, WV 26506, USA
| | - Sandra S Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80210, USA
| | - Gareth R Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80210, USA.
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Stein N, Mainali L, Hyde JS, Subczynski WK. Characterization of the distribution of spin-lattice relaxation rates of lipid spin labels in fiber cell plasma membranes of eye lenses with a stretched-exponential function. APPLIED MAGNETIC RESONANCE 2019; 50:903-918. [PMID: 31244509 PMCID: PMC6594395 DOI: 10.1007/s00723-019-01119-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/08/2018] [Revised: 02/19/2019] [Indexed: 06/02/2023]
Abstract
The stretched exponential function (SEF) was used to analyze and interpret saturation recovery (SR) electron paramagnetic resonance (EPR) data obtained from spin-labeled porcine eye-lens membranes. This function has two fitting parameters: the characteristic spin-lattice relaxation rate (T 1str -1) and the stretching parameter (β), which ranges between zero and one. When β = 1, the function is a single exponential. It is assumed that the SEF arises from a distribution of single exponential functions, each described by a T 1 value. Because T 1 -1s are determined primarily by the rotational diffusion of spin labels, they are a measure of membrane fluidity. Since β describes the distribution of T 1 -1s, it can be interpreted as a measure of membrane heterogeneity. The SEF was used to analyze SR data obtained from intact cortical and nuclear fiber cell plasma membranes extracted from the eye lenses of two-year old animals and spinlabeled with phospholipid- and cholesterol-analogs. The lipid environment sensed by these probe molecules was found to be less fluid and more heterogeneous in nuclear membranes than in cortical membranes. Parameters T 1str -1 and β were also used for a multivariate K-means cluster analysis of stretched-exponential data. This analysis indicates that SEF data can be assigned accurately to clusters in nuclear or cortical membranes. In future work, the SEF will be applied to analyze data from human eye lenses of donors with differing health histories.
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Affiliation(s)
- Natalia Stein
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, USA
| | - Laxman Mainali
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, USA
| | - James S. Hyde
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, USA
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Marsh D. Molecular order and T 1-relaxation, cross-relaxation in nitroxide spin labels. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2018; 290:38-45. [PMID: 29550514 DOI: 10.1016/j.jmr.2018.02.020] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/10/2018] [Revised: 02/26/2018] [Accepted: 02/27/2018] [Indexed: 06/08/2023]
Abstract
Interpretation of saturation-recovery EPR experiments on nitroxide spin labels whose angular rotation is restricted by the orienting potential of the environment (e.g., membranes) currently concentrates on the influence of rotational rates and not of molecular order. Here, I consider the dependence on molecular ordering of contributions to the rates of electron spin-lattice relaxation and cross relaxation from modulation of N-hyperfine and Zeeman anisotropies. These are determined by the averages 〈cos2θ〉 and 〈cos4θ〉, where θ is the angle between the nitroxide z-axis and the static magnetic field, which in turn depends on the angles that these two directions make with the director of uniaxial ordering. For saturation-recovery EPR at 9 GHz, the recovery rate constant is predicted to decrease with increasing order for the magnetic field oriented parallel to the director, and to increase slightly for the perpendicular field orientation. The latter situation corresponds to the usual experimental protocol and is consistent with the dependence on chain-labelling position in lipid bilayer membranes. An altered dependence on order parameter is predicted for saturation-recovery EPR at high field (94 GHz) that is not entirely consistent with observation. Comparisons with experiment are complicated by contributions from slow-motional components, and an unexplained background recovery rate that most probably is independent of order parameter. In general, this analysis supports the interpretation that recovery rates are determined principally by rotational diffusion rates, but experiments at other spectral positions/field orientations could increase the sensitivity to order parameter.
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Affiliation(s)
- Derek Marsh
- Max-Planck-Institut für biophysikalische Chemie, 37070 Göttingen, Germany.
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12
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Biller JR, Barnes R, Han S. Perspective of Overhauser dynamic nuclear polarization for the study of soft materials. Curr Opin Colloid Interface Sci 2018. [DOI: 10.1016/j.cocis.2018.02.007] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
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Mainali L, Camenisch TG, Hyde JS, Subczynski WK. Saturation recovery EPR spin-labeling method for quantification of lipids in biological membrane domains. APPLIED MAGNETIC RESONANCE 2017; 48:1355-1373. [PMID: 29805201 PMCID: PMC5967259 DOI: 10.1007/s00723-017-0921-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/01/2017] [Revised: 07/15/2017] [Indexed: 06/02/2023]
Abstract
The presence of integral membrane proteins induces the formation of distinct domains in the lipid bilayer portion of biological membranes. Qualitative application of both continuous wave (CW) and saturation recovery (SR) electron paramagnetic resonance (EPR) spin-labeling methods allowed discrimination of the bulk, boundary, and trapped lipid domains. A recently developed method, which is based on the CW EPR spectra of phospholipid (PL) and cholesterol (Chol) analog spin labels, allows evaluation of the relative amount of PLs (% of total PLs) in the boundary plus trapped lipid domain and the relative amount of Chol (% of total Chol) in the trapped lipid domain [M. Raguz, L. Mainali, W. J. O'Brien, and W. K. Subczynski (2015), Exp. Eye Res., 140:179-186]. Here, a new method is presented that, based on SR EPR spin-labeling, allows quantitative evaluation of the relative amounts of PLs and Chol in the trapped lipid domain of intact membranes. This new method complements the existing one, allowing acquisition of more detailed information about the distribution of lipids between domains in intact membranes. The methodological transition of the SR EPR spin-labeling approach from qualitative to quantitative is demonstrated. The abilities of this method are illustrated for intact cortical and nuclear fiber cell plasma membranes from porcine eye lenses. Statistical analysis (Student's t-test) of the data allowed determination of the separations of mean values above which differences can be treated as statistically significant (P ≤ 0.05) and can be attributed to sources other than preparation/technique.
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Affiliation(s)
| | | | | | - Witold K. Subczynski
- Corresponding Author: Witold K. Subczynski, Department of Biophysics, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA, Tel: (414) 955-4038; Fax: (414) 955-6512;
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14
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Eaton SS, Rajca A, Yang Z, Eaton GR. Azaadamantyl nitroxide spin label: complexation with β-cyclodextrin and electron spin relaxation. Free Radic Res 2017; 52:319-326. [PMID: 28946790 DOI: 10.1080/10715762.2017.1384954] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
An iodoacetamide azaadamantyl spin label was studied in fluid solution and in 9:1 trehalose:sucrose glass. In 9:1 toluene:CH2Cl2 solution at 293 K, the isotropic nitrogen hyperfine coupling is 19.2 G, T1 is 0.37 µs and T2 is 0.30-0.35 µs. Between about 80 and 150 K 1/Tm in 9:1 trehalose:sucrose is approximately independent of temperature demonstrating that the absence of methyl groups decreases 1/Tm relative to that which is observed in spin labels with methyl groups on the alpha carbons. Spin lattice relaxation rates between about 80 and 293 K in 9:1 trehalose:sucrose are similar to those observed for other nitroxide spin labels, consistent with the expectation that relaxation is dominated by Raman and local mode processes. Although complexation of the azaadamantyl spin label with β-cyclodextrin slows tumbling in aqueous solution by about a factor of 10, it has little impact on 1/T1 or 1/Tm in 9:1 trehalose:sucrose between 80 and 293 K.
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Affiliation(s)
- Sandra S Eaton
- a Department of Chemistry and Biochemistry , University of Denver , Denver , CO , USA
| | - Andrzej Rajca
- b Department of Chemistry , University of Nebraska , Lincoln , NE , USA
| | - Zhimin Yang
- b Department of Chemistry , University of Nebraska , Lincoln , NE , USA
| | - Gareth R Eaton
- a Department of Chemistry and Biochemistry , University of Denver , Denver , CO , USA
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15
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Mainali L, Raguz M, O’Brien WJ, Subczynski WK. Changes in the Properties and Organization of Human Lens Lipid Membranes Occurring with Age. Curr Eye Res 2017; 42:721-731. [PMID: 27791387 PMCID: PMC5409882 DOI: 10.1080/02713683.2016.1231325] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2016] [Revised: 08/01/2016] [Accepted: 08/28/2016] [Indexed: 10/20/2022]
Abstract
PURPOSE This research was undertaken to document the changes in the organization and properties of human lens lipid membranes that occur with age. METHODS Human lens lipid membranes prepared from the total lipids extracted from clear lens cortices and nuclei of donors from age groups 0-20 and 21-40 years were investigated. An electron paramagnetic resonance technique and nitroxide spin labels (analogues of phospholipids and cholesterol) were used. RESULTS Two distinct lipid domains, the phospholipid-cholesterol domain (PCD) and the pure cholesterol bilayer domain (CBD), were detected in all investigated membranes. Profiles of the acyl chain order, fluidity, hydrophobicity, and oxygen transport parameter across discriminated coexisting lipid domains were assessed. Independent of the age-related changes in phospholipid composition, the physical properties of the PCD remained the same for all age groups and were practically identical for cortical and nuclear membranes. However, the properties of pure CBDs changed significantly with the age of the donor and were related to the size of the CBD, which increased with the age of the donor and was greater in nuclear than in cortical membranes. A more detailed analysis revealed that the size of the CBD was determined mainly by the cholesterol content in the membrane. CONCLUSIONS This paper presents data from four age groups: 0-20, 21-40, 41-60, and 61-70 years. Data from age groups 41-60 and 61-70 years were published previously. Combining the previously published data with those data obtained in the present work allowed us to show the changes in the organization of cortical and nuclear lens lipid membranes as functions of age and cholesterol. It seems that the balance between age-related changes in membrane phospholipid composition and cholesterol content plays an integral role in the regulation of cholesterol-dependent processes in fiber cell membranes and in the maintenance of fiber cell membrane homeostasis.
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Affiliation(s)
- Laxman Mainali
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI 53226, USA
| | - Marija Raguz
- Department of Medical Physics and Biophysics, School of Medicine, University of Split, Split, Croatia
| | - William J. O’Brien
- Department of Ophthalmology, Medical College of Wisconsin, Milwaukee, WI 53226, USA
| | - Witold K. Subczynski
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI 53226, USA
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16
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High Cholesterol/Low Cholesterol: Effects in Biological Membranes: A Review. Cell Biochem Biophys 2017; 75:369-385. [PMID: 28417231 DOI: 10.1007/s12013-017-0792-7] [Citation(s) in RCA: 183] [Impact Index Per Article: 26.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2017] [Accepted: 03/27/2017] [Indexed: 12/11/2022]
Abstract
Lipid composition determines membrane properties, and cholesterol plays a major role in this determination as it regulates membrane fluidity and permeability, as well as induces the formation of coexisting phases and domains in the membrane. Biological membranes display a very diverse lipid composition, the lateral organization of which plays a crucial role in regulating a variety of membrane functions. We hypothesize that, during biological evolution, membranes with a particular cholesterol content were selected to perform certain functions in the cells of eukaryotic organisms. In this review, we discuss the major membrane properties induced by cholesterol, and their relationship to certain membrane functions.
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17
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Marsh D. Coherence transfer and electron T 1-, T 2-relaxation in nitroxide spin labels. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2017; 277:86-94. [PMID: 28258025 DOI: 10.1016/j.jmr.2017.02.006] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/27/2016] [Revised: 02/08/2017] [Accepted: 02/09/2017] [Indexed: 06/06/2023]
Abstract
Abragam's double-commutator spin operator method is used to analyse: 1) electron coherence transfer by intermolecular dipolar interaction between spin-label radicals, and 2) longitudinal and transverse electron spin relaxation by rotational modulation of the Zeeman and nitrogen-hyperfine anisotropies of isolated nitroxide spin labels. Results compatible with earlier treatments by Redfield theory are obtained without specifically evaluating matrix elements. Extension to single-transition operators for isolated nitroxides predicts electron coherence transfer by pseudosecular electron-nuclear dipolar interaction, in the absence of intermolecular dipolar coupling. This explains earlier experimental findings that coherence transfer (specifically dispersion-like distortion of the EPR absorption line shape) does not extrapolate to zero at low concentrations of nitroxide spin labels.
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Affiliation(s)
- Derek Marsh
- Max-Planck-Institut für biophysikalische Chemie, 37070 Göttingen, Germany; University of Southern Denmark, MEMPHYS-Centre for Biomembrane Physics, Campusvej 55, 5230 Odense M, Denmark.
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18
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Marsh D. Cross relaxation in nitroxide spin labels. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2016; 272:172-180. [PMID: 27717659 DOI: 10.1016/j.jmr.2016.09.014] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/27/2016] [Revised: 09/14/2016] [Accepted: 09/18/2016] [Indexed: 06/06/2023]
Abstract
Cross relaxation, and mI-dependence of the intrinsic electron spin-lattice relaxation rate We, are incorporated explicitly into the rate equations for the electron-spin population differences that govern the saturation behaviour of 14N- and 15N-nitroxide spin labels. Both prove important in spin-label EPR and ELDOR, particularly for saturation recovery studies. Neither for saturation recovery, nor for CW-saturation EPR and CW-ELDOR, can cross relaxation be described simply by increasing the value of We, the intrinsic spin-lattice relaxation rate. Independence of the saturation recovery rates from the hyperfine line pumped or observed follows directly from solution of the rate equations including cross relaxation, even when the intrinsic spin-lattice relaxation rate We is mI-dependent.
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Affiliation(s)
- Derek Marsh
- Max-Planck-Institut für biophysikalische Chemie, 37070 Göttingen, Germany; University of Southern Denmark, MEMPHYS-Centre for Biomembrane Physics, Campusvej 55, 5230 Odense M, Denmark.
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19
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Goslar J, Hoffmann SK, Lijewski S. Dynamics of 4-oxo-TEMPO-d16-(15)N nitroxide-propylene glycol system studied by ESR and ESE in liquid and glassy state in temperature range 10-295K. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2016; 269:162-175. [PMID: 27323281 DOI: 10.1016/j.jmr.2016.06.006] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/30/2016] [Revised: 06/07/2016] [Accepted: 06/08/2016] [Indexed: 06/06/2023]
Abstract
ESR spectra and electron spin relaxation of nitroxide radical in 4-oxo-TEMPO-d16-(15)N in propylene glycol were studied at X-band in the temperature range 10-295K. The spin-lattice relaxation in the liquid viscous state determined from the resonance line shape is governed by three mechanisms occurring during isotropic molecular reorientations. In the glassy state below 200K the spin-lattice relaxation, phase relaxation and electron spin echo envelope modulations (ESEEM) were studied by pulse spin echo technique using 2-pulse and 3-pulse induced signals. Electron spin-lattice relaxation is governed by a single non-phonon relaxation process produced by localized oscillators of energy 76cm(-1). Electron spin dephasing is dominated by a molecular motion producing a resonance-type peak in the temperature dependence of the dephasing rate around 120K. The origin of the peak is discussed and a simple method for the peak shape analysis is proposed, which gives the activation energy of a thermally activated motion Ea=7.8kJ/mol and correlation time τ0=10(-8)s. The spin echo amplitude is strongly modulated and FT spectrum contains a doublet of lines centered around the (2)D nuclei Zeeman frequency. The splitting into the doublet is discussed as due to a weak hyperfine coupling of nitroxide unpaired electron with deuterium of reorienting CD3 groups.
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Affiliation(s)
- Janina Goslar
- Institute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego 17, 60-179 Poznan, Poland
| | - Stanislaw K Hoffmann
- Institute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego 17, 60-179 Poznan, Poland.
| | - Stefan Lijewski
- Institute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego 17, 60-179 Poznan, Poland
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20
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Eaton SS, Eaton GR. Multifrequency Pulsed EPR and the Characterization of Molecular Dynamics. Methods Enzymol 2015; 563:37-58. [PMID: 26478481 PMCID: PMC5380387 DOI: 10.1016/bs.mie.2015.06.028] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/08/2023]
Abstract
In fluid solution, motion-dependent processes dominate electron spin-lattice relaxation for nitroxides and semiquinones at frequencies between 250 MHz and 34 GHz. For triarylmethyl radicals, motion-dependent processes dominate spin-lattice relaxation at frequencies below about 3 GHz. The frequency dependence of relaxation provides invaluable information about dynamic processes occurring with characteristic times on the order of the electron Zeeman frequency. Relaxation mechanisms, methods of measuring spin-lattice relaxation, and motional processes for nitroxide, semiquinone, and triarylmethyl radicals are discussed.
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Affiliation(s)
- Sandra S Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, Colorado, USA.
| | - Gareth R Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, Colorado, USA
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21
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Klein JH, Schmidt D, Steiner UE, Lambert C. Complete Monitoring of Coherent and Incoherent Spin Flip Domains in the Recombination of Charge-Separated States of Donor-Iridium Complex-Acceptor Triads. J Am Chem Soc 2015; 137:11011-21. [DOI: 10.1021/jacs.5b04868] [Citation(s) in RCA: 48] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Affiliation(s)
- Johannes H. Klein
- Wilhelm
Conrad Röntgen Research Center for Complex Material Systems,
Würzburg, Center for Nanosystems Chemistry, Institut für Organische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - David Schmidt
- Wilhelm
Conrad Röntgen Research Center for Complex Material Systems,
Würzburg, Center for Nanosystems Chemistry, Institut für Organische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | | | - Christoph Lambert
- Wilhelm
Conrad Röntgen Research Center for Complex Material Systems,
Würzburg, Center for Nanosystems Chemistry, Institut für Organische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
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22
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Raguz M, Mainali L, O'Brien WJ, Subczynski WK. Lipid domains in intact fiber-cell plasma membranes isolated from cortical and nuclear regions of human eye lenses of donors from different age groups. Exp Eye Res 2015; 132:78-90. [PMID: 25617680 DOI: 10.1016/j.exer.2015.01.018] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2014] [Revised: 01/05/2015] [Accepted: 01/20/2015] [Indexed: 02/02/2023]
Abstract
The results reported here clearly document changes in the properties and the organization of fiber-cell membrane lipids that occur with age, based on electron paramagnetic resonance (EPR) analysis of lens membranes of clear lenses from donors of age groups from 0 to 20, 21 to 40, and 61 to 80 years. The physical properties, including profiles of the alkyl chain order, fluidity, hydrophobicity, and oxygen transport parameter, were investigated using EPR spin-labeling methods, which also provide an opportunity to discriminate coexisting lipid domains and to evaluate the relative amounts of lipids in these domains. Fiber-cell membranes were found to contain three distinct lipid environments: bulk lipid domain, which appears minimally affected by membrane proteins, and two domains that appear due to the presence of membrane proteins, namely boundary and trapped lipid domains. In nuclear membranes the amount of boundary and trapped phospholipids as well as the amount of cholesterol in trapped lipid domains increased with the donors' age and was greater than that in cortical membranes. The difference between the amounts of lipids in domains uniquely formed due to the presence of membrane proteins in nuclear and cortical membranes increased with the donors' age. It was also shown that cholesterol was to a large degree excluded from trapped lipid domains in cortical membranes. It is evident that the rigidity of nuclear membranes was greater than that of cortical membranes for all age groups. The amount of lipids in domains of low oxygen permeability, mainly in trapped lipid domains, were greater in nuclear than cortical membranes and increased with the age of donors. These results indicate that the nuclear fiber cell plasma membranes were less permeable to oxygen than cortical membranes and become less permeable to oxygen with age. In clear lenses, age-related changes in the lens lipid and protein composition and organization appear to occur in ways that increase fiber cell plasma membrane resistance to oxygen permeation.
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Affiliation(s)
- Marija Raguz
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI 53226, USA; Department of Medical Physics and Biophysics, School of Medicine, University of Split, Split, Croatia
| | - Laxman Mainali
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI 53226, USA
| | - William J O'Brien
- Department of Ophthalmology, Medical College of Wisconsin, Milwaukee, WI 53226, USA
| | - Witold K Subczynski
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI 53226, USA.
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23
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Yang Z, Bridges M, Lerch MT, Altenbach C, Hubbell WL. Saturation Recovery EPR and Nitroxide Spin Labeling for Exploring Structure and Dynamics in Proteins. Methods Enzymol 2015; 564:3-27. [DOI: 10.1016/bs.mie.2015.07.016] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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24
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Properties of membranes derived from the total lipids extracted from clear and cataractous lenses of 61-70-year-old human donors. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2014; 44:91-102. [PMID: 25502634 DOI: 10.1007/s00249-014-1004-7] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/15/2014] [Revised: 11/18/2014] [Accepted: 11/28/2014] [Indexed: 10/24/2022]
Abstract
Human lens-lipid membranes prepared from the total lipids extracted from clear and cataractous lens cortexes and nuclei of 61-70-year-old donors by use of a rapid solvent-exchange method were investigated. The measured cholesterol-to-phospholipid (Chol/PL) molar ratio in these membranes was 1.8 and 4.4 for cortex and nucleus of clear lenses, respectively, and 1.14 and 1.45 for cataractous lenses. Properties and organization of the lipid bilayer were investigated by use of electron paramagnetic resonance spin-labeling methods. Formation of Chol crystals was confirmed by use of differential scanning calorimetry. Pure cholesterol bilayer domains (CBDs) were formed in all the membranes investigated. It was shown that in clear lens membranes of the nucleus, Chol exists in three different environments: (1) dispersed in phospholipid bilayers (PCDs), (2) in CBDs, and (3) in Chol crystals. In clear lens membranes of the cortex, and in cortical and nuclear cataractous lens membranes, Chol crystals were not detected, because of the lower Chol content. Profiles of membrane properties (alkyl-chain order, fluidity, oxygen transport, and hydrophobicity) across the PCD were very similar for clear and cataractous membranes. Profiles of the oxygen transport parameter across the CBD were, however, different for cortical clear and cataractous membranes-the amount and size of CBDs was less in cataractous membranes. These results suggest that high Chol content, formation of CBDs, and formation of Chol crystals should not be regarded as major predispositions for the development of age-related cataracts.
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25
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Elajaili HB, Biller JR, Eaton SS, Eaton GR. Frequency dependence of electron spin-lattice relaxation for semiquinones in alcohol solutions. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2014; 247:81-87. [PMID: 25261741 PMCID: PMC4224960 DOI: 10.1016/j.jmr.2014.08.014] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/16/2014] [Revised: 08/06/2014] [Accepted: 08/28/2014] [Indexed: 05/31/2023]
Abstract
The spin-lattice relaxation rates at 293 K for three anionic semiquinones (2,5-di-t-butyl-1,4-benzosemiquinone, 2,6-di-t-butyl-1,4-benzosemiquinone, and 2,3,5,6-tetramethoxy-1,4-benzosemiquinone) were studied at up to 8 frequencies between 250 MHz and 34 GHz in ethanol or methanol solution containing high concentrations of OH(-). The relaxation rates are about a factor of 2 faster at lower frequencies than at 9 or 34 GHz. However, in perdeuterated alcohols the relaxation rates exhibit little frequency dependence, which demonstrates that the dominant frequency-dependent contribution to relaxation is modulation of dipolar interactions with solvent nuclei. The relaxation rates were modeled as the sum of two frequency-independent contributions (spin rotation and a local mode) and two frequency-dependent contributions (modulation of dipolar interaction with solvent nuclei and a much smaller contribution from modulation of g anisotropy). The correlation time for modulation of the interaction with solvent nuclei is longer than the tumbling correlation time of the semiquinone and is consistent with hydrogen bonding of the alcohol to the oxygen atoms of the semiquinones.
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Affiliation(s)
- Hanan B Elajaili
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208, USA
| | - Joshua R Biller
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208, USA
| | - Sandra S Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208, USA
| | - Gareth R Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208, USA.
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26
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Raguz M, Mainali L, O'Brien WJ, Subczynski WK. Lipid-protein interactions in plasma membranes of fiber cells isolated from the human eye lens. Exp Eye Res 2014; 120:138-51. [PMID: 24486794 DOI: 10.1016/j.exer.2014.01.018] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2013] [Revised: 01/20/2014] [Accepted: 01/22/2014] [Indexed: 11/19/2022]
Abstract
The protein content in human lens membranes is extremely high, increases with age, and is higher in the nucleus as compared with the cortex, which should strongly affect the organization and properties of the lipid bilayer portion of intact membranes. To assess these effects, the intact cortical and nuclear fiber cell plasma membranes isolated from human lenses from 41- to 60-year-old donors were studied using electron paramagnetic resonance spin-labeling methods. Results were compared with those obtained for lens lipid membranes prepared from total lipid extracts from human eyes of the same age group [Mainali, L., Raguz, M., O'Brien, W. J., and Subczynski, W. K. (2013) Biochim. Biophys. Acta]. Differences were considered to be mainly due to the effect of membrane proteins. The lipid-bilayer portions of intact membranes were significantly less fluid than lipid bilayers of lens lipid membranes, prepared without proteins. The intact membranes were found to contain three distinct lipid environments termed the bulk lipid domain, boundary lipid domain, and trapped lipid domain. However, the cholesterol bilayer domain, which was detected in cortical and nuclear lens lipid membranes, was not detected in intact membranes. The relative amounts of bulk and trapped lipids were evaluated. The amount of lipids in domains uniquely formed due to the presence of membrane proteins was greater in nuclear membranes than in cortical membranes. Thus, it is evident that the rigidity of nuclear membranes is greater than that of cortical membranes. Also the permeability coefficients for oxygen measured in domains of nuclear membranes were significantly lower than appropriate coefficients measured in cortical membranes. Relationships between the organization of lipids into lipid domains in fiber cells plasma membranes and the organization of membrane proteins are discussed.
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Affiliation(s)
- Marija Raguz
- Department of Biophysics, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA; Department of Medical Physics and Biophysics, School of Medicine, University of Split, Split, Croatia
| | - Laxman Mainali
- Department of Biophysics, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA
| | - William J O'Brien
- Department of Ophthalmology, Medical College of Wisconsin, Milwaukee, WI 53226, USA
| | - Witold K Subczynski
- Department of Biophysics, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA.
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27
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Biller JR, Elajaili H, Meyer V, Rosen GM, Eaton SS, Eaton GR. Electron spin-lattice relaxation mechanisms of rapidly-tumbling nitroxide radicals. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2013; 236:47-56. [PMID: 24056272 PMCID: PMC3952064 DOI: 10.1016/j.jmr.2013.08.006] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/22/2012] [Revised: 08/13/2013] [Accepted: 08/14/2013] [Indexed: 05/12/2023]
Abstract
Electron spin relaxation times at 295 K were measured at frequencies between 250 MHz and 34 GHz for perdeuterated 2,2,6,6-tetramethyl-4-piperidone-1-oxyl (PDT) in five solvents with viscosities that result in tumbling correlation times, τR, between 4 and 50 ps and for three (14)N/(15)N pairs of nitroxides in water with τR between 9 and 19 ps. To test the impact of structure on relaxation three additional nitroxides with τR between 10 and 26 ps were studied. In this fast tumbling regime T2(-1)~T1(-1) at frequencies up to about 9 GHz. At 34 GHz T2(-1)>T1(-1) due to increased contributions to T2(-1) from incomplete motional averaging of g-anisotropy, and T2(-1)-T1(-1) is proportional to τR. The contribution to T1(-1) from spin rotation is independent of frequency and decreases as τR increases. Spin rotation dominates T1(-1) at 34 GHz for all τR studied, and at all frequencies studied for τR=4 ps. The contribution to T1(-1) from modulation of nitrogen hyperfine anisotropy increases as frequency decreases and as τR increases; it dominates at low frequencies for τR>~15 ps. The contribution from modulation of g anisotropy is significant only at 34 GHz. Inclusion of a thermally-activated process was required to account for the observation that for most of the radicals, T1(-1) was smaller at 250 MHz than at 1-2 GHz. The significant (15)N/(14)N isotope effect, the small H/D isotope effect, and the viscosity dependence of the magnitude of the contribution from the thermally-activated process suggest that it arises from intramolecular motions of the nitroxide ring that modulate the isotropic A values.
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Affiliation(s)
- Joshua R. Biller
- Department of Chemistry and Biochemistry and Center for EPR Imaging In Vivo Physiology, University of Denver, Denver, CO 80208
| | - Hanan Elajaili
- Department of Chemistry and Biochemistry and Center for EPR Imaging In Vivo Physiology, University of Denver, Denver, CO 80208
| | - Virginia Meyer
- Department of Chemistry and Biochemistry and Center for EPR Imaging In Vivo Physiology, University of Denver, Denver, CO 80208
| | - Gerald M. Rosen
- Department of Pharmaceutical Sciences, Center for EPR Imaging in Vivo Physiology, and Center for Biomedical Engineering and Technology, University of Maryland, Baltimore, MD 21201
| | - Sandra S. Eaton
- Department of Chemistry and Biochemistry and Center for EPR Imaging In Vivo Physiology, University of Denver, Denver, CO 80208
| | - Gareth R. Eaton
- Department of Chemistry and Biochemistry and Center for EPR Imaging In Vivo Physiology, University of Denver, Denver, CO 80208
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28
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Mainali L, Raguz M, O'Brien WJ, Subczynski WK. Properties of membranes derived from the total lipids extracted from the human lens cortex and nucleus. BIOCHIMICA ET BIOPHYSICA ACTA 2013; 1828:1432-40. [PMID: 23438364 PMCID: PMC3633468 DOI: 10.1016/j.bbamem.2013.02.006] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/09/2012] [Revised: 02/08/2013] [Accepted: 02/14/2013] [Indexed: 11/21/2022]
Abstract
Human lens lipid membranes prepared using a rapid solvent exchange method from the total lipids extracted from the clear lens cortex and nucleus of 41- to 60-year-old donors were investigated using electron paramagnetic resonance spin-labeling. Profiles of the phospholipid alkyl-chain order, fluidity, oxygen transport parameter, and hydrophobicity were assessed across coexisting membrane domains. Membranes prepared from the lens cortex and nucleus were found to contain two distinct lipid environments, the bulk phospholipid-cholesterol domain and the cholesterol bilayer domain (CBD). The alkyl chains of phospholipids were strongly ordered at all depths, indicating that the amplitude of the wobbling motion of alkyl chains was small. However, profiles of the membrane fluidity, which explicitly contain time (expressed as the spin-lattice relaxation rate) and depend on the rotational motion of spin labels, show relatively high fluidity of alkyl chains close to the membrane center. Profiles of the oxygen transport parameter and hydrophobicity have a rectangular shape and also indicate a high fluidity and hydrophobicity of the membrane center. The amount of CBD was greater in nuclear membranes than in cortical membranes. The presence of the CBD in lens lipid membranes, which at 37°C showed a permeability coefficient for oxygen about 60% smaller than across a water layer of the same thickness, would be expected to raise the barrier for oxygen transport across the fiber cell membrane. Properties of human membranes are compared with those obtained for membranes made of lipids extracted from cortex and nucleus of porcine and bovine eye lenses.
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Affiliation(s)
- Laxman Mainali
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI 53226, USA
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29
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Mainali L, Hyde JS, Subczynski WK. Using spin-label W-band EPR to study membrane fluidity profiles in samples of small volume. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2013; 226:35-44. [PMID: 23207176 PMCID: PMC3529815 DOI: 10.1016/j.jmr.2012.11.001] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/13/2012] [Revised: 10/15/2012] [Accepted: 11/03/2012] [Indexed: 05/18/2023]
Abstract
Conventional and saturation-recovery (SR) EPR at W-band (94GHz) using phosphatidylcholine spin labels (labeled at the alkyl chain [n-PC] and headgroup [T-PC]) to obtain profiles of membrane fluidity has been demonstrated. Dimyristoylphosphatidylcholine (DMPC) membranes with and without 50 mol% cholesterol have been studied, and the results have been compared with similar studies at X-band (9.4 GHz) (L. Mainali, J.B. Feix, J.S. Hyde, W.K. Subczynski, J. Magn. Reson. 212 (2011) 418-425). Profiles of the spin-lattice relaxation rate (T(1)(-1)) obtained from SR EPR measurements for n-PCs and T-PC were used as a convenient quantitative measure of membrane fluidity. Additionally, spectral analysis using Freed's MOMD (microscopic-order macroscopic-disorder) model (E. Meirovitch, J.H. Freed J. Phys. Chem. 88 (1984) 4995-5004) provided rotational diffusion coefficients (R(perpendicular) and R(||)) and order parameters (S(0)). Spectral analysis at X-band provided one rotational diffusion coefficient, R(perpendicular). T(1)(-1), R(perpendicular), and R(||) profiles reflect local membrane dynamics of the lipid alkyl chain, while the order parameter shows only the amplitude of the wobbling motion of the lipid alkyl chain. Using these dynamic parameters, namely T(1)(-1), R(perpendicular), and R(||), one can discriminate the different effects of cholesterol at different depths, showing that cholesterol has a rigidifying effect on alkyl chains to the depth occupied by the rigid steroid ring structure and a fluidizing effect at deeper locations. The nondynamic parameter, S(0), shows that cholesterol has an ordering effect on alkyl chains at all depths. Conventional and SR EPR measurements with T-PC indicate that cholesterol has a fluidizing effect on phospholipid headgroups. EPR at W-band provides more detailed information about the depth-dependent dynamic organization of the membrane compared with information obtained at X-band. EPR at W-band has the potential to be a powerful tool for studying membrane fluidity in samples of small volume, ~30 nL, compared with a representative sample volume of ~3 μL at X-band.
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Affiliation(s)
| | | | - Witold K. Subczynski
- Author to whom correspondence should be addressed: Witold Karol Subczynski, Ph.D., D.Sc., Department of Biophysics, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226-0509, Phone: (414) 456-4038, Fax: (414) 456-6512,
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Biller JR, Meyer VM, Elajaili H, Rosen GM, Eaton SS, Eaton GR. Frequency dependence of electron spin relaxation times in aqueous solution for a nitronyl nitroxide radical and perdeuterated-tempone between 250 MHz and 34 GHz. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2012; 225:52-7. [PMID: 23123770 PMCID: PMC3538045 DOI: 10.1016/j.jmr.2012.10.002] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/23/2012] [Revised: 10/04/2012] [Accepted: 10/07/2012] [Indexed: 05/16/2023]
Abstract
Electron spin relaxation times of perdeuterated tempone (PDT) 1 and of a nitronyl nitroxide (2-(4-carboxy-phenyl)-4,4,5,5-tetramethylimidazoline-3-oxide-1-oxyl) 2 in aqueous solution at room temperature were measured by 2-pulse electron spin echo (T(2)) or 3-pulse inversion recovery (T(1)) in the frequency range of 250 MHz to 34 GHz. At 9 GHz values of T(1) measured by long-pulse saturation recovery were in good agreement with values determined by inversion recovery. Below 9 GHz for 1 and below 1.5 GHz for 2,T(1)~T(2), as expected in the fast tumbling regime. At higher frequencies T(2) was shorter than T(1) due to incomplete motional averaging of g and A anisotropy. The frequency dependence of 1/T(1) is modeled as the sum of spin rotation, modulation of g and A-anisotropy, and a thermally-activated process that has maximum contribution at about 1.5 GHz. The spin lattice relaxation times for the nitronyl nitroxide were longer than for PDT by a factor of about 2 at 34 GHz, decreasing to about a factor of 1.5 at 250 MHz. The rotational correlation times, τ(R) are calculated to be 9 ps for 1 and about 25 ps for 2. The longer spin lattice relaxation times for 2 than for 1 at 9 and 34 GHz are due predominantly to smaller contributions from spin rotation that arise from slower tumbling. The smaller nitrogen hyperfine couplings for the nitronyl 2 than for 1 decrease the contribution to relaxation due to modulation of A anisotropy. However, at lower frequencies the slower tumbling of 2 results in a larger value of ωτ(R) (ω is the resonance frequency) and larger values of the spectral density function, which enhances the contribution from modulation of anisotropic interactions for 2 to a greater extent than for 1.
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Affiliation(s)
- Joshua R. Biller
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208
- Center for EPR Imaging in Vivo Physiology, University of Denver, Denver, CO 80208 and University of Maryland, Baltimore, Baltimore, MD, 21201
| | - Virginia M. Meyer
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208
- Center for EPR Imaging in Vivo Physiology, University of Denver, Denver, CO 80208 and University of Maryland, Baltimore, Baltimore, MD, 21201
| | - Hanan Elajaili
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208
- Center for EPR Imaging in Vivo Physiology, University of Denver, Denver, CO 80208 and University of Maryland, Baltimore, Baltimore, MD, 21201
| | - Gerald M. Rosen
- Center for EPR Imaging in Vivo Physiology, University of Denver, Denver, CO 80208 and University of Maryland, Baltimore, Baltimore, MD, 21201
- Center for Biomedical Engineering and Technology, University of Maryland, Baltimore, Baltimore, MD, 21201
- Department of Pharmaceutical Sciences, University of Maryland, Baltimore, Baltimore, MD, 21201
| | - Sandra S. Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208
- Center for EPR Imaging in Vivo Physiology, University of Denver, Denver, CO 80208 and University of Maryland, Baltimore, Baltimore, MD, 21201
| | - Gareth R. Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208
- Center for EPR Imaging in Vivo Physiology, University of Denver, Denver, CO 80208 and University of Maryland, Baltimore, Baltimore, MD, 21201
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Collauto A, Barbon A, Brustolon M. First determination of the spin relaxation properties of a nitronyl nitroxide in solution by electron spin echoes at X-band: a comparison with Tempone. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2012; 223:180-186. [PMID: 22975247 DOI: 10.1016/j.jmr.2012.07.011] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/15/2012] [Revised: 07/12/2012] [Accepted: 07/13/2012] [Indexed: 06/01/2023]
Abstract
We studied by electron spin echo pulse methods the spin relaxation properties of a phenyl nitronyl nitroxide radical (2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide, PTIO) at X-band in fluid toluene solution in a wide temperature range, and in a water/glycerol 1:1 mixture near room temperature. The relaxation properties of PTIO have been compared with that of Tempone, as a widely used nitroxide. By a new procedure, based on experimental results on the temperature dependences of the relaxation times T(1) and T(2), and on the approximation of an isotropic brownian rotational diffusion, we separated non-secular, spin rotational and residual terms from the transverse relaxation rate to isolate secular and pseudosecular contributions. By comparing the results for the two radicals we found the differences in the magnetic properties that give rise to slower transverse (T(2)) and longitudinal (T(1)) electron spin relaxation for PTIO in the whole temperature range explored in this work.
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Affiliation(s)
- A Collauto
- Dipartimento di Scienze Chimiche, Università degli Studi di Padova, Via Marzolo 1, I-35131 Padova, Italy
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Rangel DP, Baveye PC, Robinson BH. Direct simulation of magnetic resonance relaxation rates and line shapes from molecular trajectories. J Phys Chem B 2012; 116:6233-49. [PMID: 22540276 PMCID: PMC3398626 DOI: 10.1021/jp2062628] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We simulate spin relaxation processes, which may be measured by either continuous wave or pulsed magnetic resonance techniques, using trajectory-based simulation methodologies. The spin-lattice relaxation rates are extracted numerically from the relaxation simulations. The rates obtained from the numerical fitting of the relaxation curves are compared to those obtained by direct simulation from the relaxation Bloch-Wangsness-Abragam-Redfield theory (BWART). We have restricted our study to anisotropic rigid-body rotational processes, and to the chemical shift anisotropy (CSA) and a single spin-spin dipolar (END) coupling mechanisms. Examples using electron paramagnetic resonance (EPR) nitroxide and nuclear magnetic resonance (NMR) deuterium quadrupolar systems are provided. The objective is to compare those rates obtained by numerical simulations with the rates obtained by BWART. There is excellent agreement between the simulated and BWART rates for a Hamiltonian describing a single spin (an electron) interacting with the bath through the chemical shift anisotropy (CSA) mechanism undergoing anisotropic rotational diffusion. In contrast, when the Hamiltonian contains both the chemical shift anisotropy (CSA) and the spin-spin dipolar (END) mechanisms, the decay rate of a single exponential fit of the simulated spin-lattice relaxation rate is up to a factor of 0.2 smaller than that predicted by BWART. When the relaxation curves are fit to a double exponential, the slow and fast rates extracted from the decay curves bound the BWART prediction. An extended BWART theory, in the literature, includes the need for multiple relaxation rates and indicates that the multiexponential decay is due to the combined effects of direct and cross-relaxation mechanisms.
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Affiliation(s)
- David P Rangel
- Department of Chemistry, University of Washington, Seattle, Washington 98195, United States.
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Mainali L, Feix JB, Hyde JS, Subczynski WK. Membrane fluidity profiles as deduced by saturation-recovery EPR measurements of spin-lattice relaxation times of spin labels. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2011; 212:418-25. [PMID: 21868272 PMCID: PMC3214655 DOI: 10.1016/j.jmr.2011.07.022] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/20/2011] [Revised: 07/07/2011] [Accepted: 07/28/2011] [Indexed: 05/18/2023]
Abstract
There are no easily obtainable EPR spectral parameters for lipid spin labels that describe profiles of membrane fluidity. The order parameter, which is most often used as a measure of membrane fluidity, describes the amplitude of wobbling motion of alkyl chains relative to the membrane normal and does not contain explicitly time or velocity. Thus, this parameter can be considered as nondynamic. The spin-lattice relaxation rate (T(1)(-1)) obtained from saturation-recovery EPR measurements of lipid spin labels in deoxygenated samples depends primarily on the rotational correlation time of the nitroxide moiety within the lipid bilayer. Thus, T(1)(-1) can be used as a convenient quantitative measure of membrane fluidity that reflects local membrane dynamics. T(1)(-1) profiles obtained for 1-palmitoyl-2-(n-doxylstearoyl)phosphatidylcholine (n-PC) spin labels in dimyristoylphosphatidylcholine (DMPC) membranes with and without 50 mol% cholesterol are presented in parallel with profiles of the rotational diffusion coefficient, R(⊥), obtained from simulation of EPR spectra using Freed's model. These profiles are compared with profiles of the order parameter obtained directly from EPR spectra and with profiles of the order parameter obtained from simulation of EPR spectra. It is shown that T(1)(-1) and R(⊥) profiles reveal changes in membrane fluidity that depend on the motional properties of the lipid alkyl chain. We find that cholesterol has a rigidifying effect only to the depth occupied by the rigid steroid ring structure and a fluidizing effect at deeper locations. These effects cannot be differentiated by profiles of the order parameter. All profiles in this study were obtained at X-band (9.5 GHz).
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Affiliation(s)
- Laxman Mainali
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI, USA
| | - Jimmy B. Feix
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI, USA
| | - James S. Hyde
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI, USA
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Biller JR, Meyer V, Elajaili H, Rosen GM, Kao JP, Eaton SS, Eatona GR. Relaxation times and line widths of isotopically-substituted nitroxides in aqueous solution at X-band. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2011; 212:370-7. [PMID: 21843961 PMCID: PMC3196672 DOI: 10.1016/j.jmr.2011.07.018] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/06/2011] [Revised: 07/21/2011] [Accepted: 07/22/2011] [Indexed: 05/16/2023]
Abstract
Optimization of nitroxides as probes for EPR imaging requires detailed understanding of spectral properties. Spin lattice relaxation times, spin packet line widths, nuclear hyperfine splitting, and overall lineshapes were characterized for six low molecular weight nitroxides in dilute deoxygenated aqueous solution at X-band. The nitroxides included 6-member, unsaturated 5-member, or saturated 5-member rings, most of which were isotopically labeled. The spectra are near the fast tumbling limit with T(1)∼T(2) in the range of 0.50-1.1 μs at ambient temperature. Both spin-lattice relaxation T(1) and spin-spin relaxation T(2) are longer for (15)N- than for (14)N-nitroxides. The dominant contributions to T(1) are modulation of nitrogen hyperfine anisotropy and spin rotation. Dependence of T(1) on nitrogen nuclear spin state m(I) was observed for both (14)N and (15)N. Unresolved hydrogen/deuterium hyperfine couplings dominate overall line widths. Lineshapes were simulated by including all nuclear hyperfine couplings and spin packet line widths that agreed with values obtained by electron spin echo. Line widths and relaxation times are predicted to be about the same at 250 MHz as at X-band.
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Affiliation(s)
- Joshua R. Biller
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208
- Center for EPR Imaging in Vivo Physiology, University of Denver, Denver, CO 80208 and University of Maryland, Baltimore, Baltimore, MD, 21201
| | - Virginia Meyer
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208
- Center for EPR Imaging in Vivo Physiology, University of Denver, Denver, CO 80208 and University of Maryland, Baltimore, Baltimore, MD, 21201
| | - Hanan Elajaili
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208
- Center for EPR Imaging in Vivo Physiology, University of Denver, Denver, CO 80208 and University of Maryland, Baltimore, Baltimore, MD, 21201
| | - Gerald M. Rosen
- Center for EPR Imaging in Vivo Physiology, University of Denver, Denver, CO 80208 and University of Maryland, Baltimore, Baltimore, MD, 21201
- Center for Biomedical Engineering and Technology, University of Maryland, Baltimore, Baltimore, MD, 21201
- Department of Pharmaceutical Sciences, University of Maryland, Baltimore, Baltimore, MD, 21201
| | - Joseph P.Y. Kao
- Center for EPR Imaging in Vivo Physiology, University of Denver, Denver, CO 80208 and University of Maryland, Baltimore, Baltimore, MD, 21201
- Center for Biomedical Engineering and Technology, University of Maryland, Baltimore, Baltimore, MD, 21201
- Department of Physiology, University of Maryland, Baltimore, Baltimore, MD, 21201
| | - Sandra S. Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208
- Center for EPR Imaging in Vivo Physiology, University of Denver, Denver, CO 80208 and University of Maryland, Baltimore, Baltimore, MD, 21201
| | - Gareth R. Eatona
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208
- Center for EPR Imaging in Vivo Physiology, University of Denver, Denver, CO 80208 and University of Maryland, Baltimore, Baltimore, MD, 21201
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Mainali L, Raguz M, Camenisch TG, Hyde JS, Subczynski WK. Spin-label saturation-recovery EPR at W-band: applications to eye lens lipid membranes. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2011; 212:86-94. [PMID: 21745756 PMCID: PMC3163743 DOI: 10.1016/j.jmr.2011.06.014] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/24/2011] [Revised: 06/15/2011] [Accepted: 06/16/2011] [Indexed: 05/03/2023]
Abstract
Saturation-recovery (SR) EPR at W-band (94 GHz) to obtain profiles of the membrane fluidity and profiles of the oxygen transport parameter is demonstrated for lens lipid membranes using phosphatidylcholine (n-PC), stearic acid (n-SASL), and cholesterol analog (ASL and CSL) spin labels, and compared with results obtained in parallel experiments at X-band (9.4 GHz). Membranes were derived from the total lipids extracted from 2-year-old porcine lens cortex and nucleus. Two findings are especially significant. First, measurements of the spin-lattice relaxation times T1 for n-PCs allowed T1 profiles across the membrane to be obtained. These profiles reflect local membrane properties differently than profiles of the order parameter. Profiles obtained at W-band are, however, shifted to longer T1 values compared to those obtained at X-band. Second, using cholesterol analog spin labels and relaxation agents (hydrophobic oxygen and water-soluble NiEDDA), the cholesterol bilayer domain was discriminated in membranes made from lipids of the lens nucleus. However, membranes made from cortical lipids show a single homogeneous environment. Profiles of the oxygen transport parameter obtained from W-band measurements are practically identical to those obtained from X-band measurements, and are very similar to those obtained earlier at X-band for membranes made of 2-year-old bovine cortical and nuclear lens lipids (M. Raguz, J. Widomska, J. Dillon, E.R. Gaillard, W.K. Subczynski, Biochim. Biophys. Acta 1788 (2009) 2380-2388). Results demonstrate that SR EPR at W-band has the potential to be a powerful tool for studying samples of small volume, ∼30 nL, compared with the sample volume of ∼3 μL at X-band.
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Affiliation(s)
- Laxman Mainali
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI 53226, USA
| | - Marija Raguz
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI 53226, USA
- Department of Medical Physics and Biophysics, School of Medicine, University of Split, Split, Croatia
| | | | - James S. Hyde
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI 53226, USA
| | - Witold K. Subczynski
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI 53226, USA
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Sato H, Kathirvelu V, Fielding A, Blinco JP, Micallef AS, Bottle SE, Eaton SS, Eaton GR. Impact of molecular size on electron spin relaxation rates of nitroxyl radicals in glassy solvents between 100 and 300 K. Mol Phys 2010. [DOI: 10.1080/00268970701724966] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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Bridges MD, Hideg K, Hubbell WL. Resolving Conformational and Rotameric Exchange in Spin-Labeled Proteins Using Saturation Recovery EPR. APPLIED MAGNETIC RESONANCE 2010; 37:363. [PMID: 20157634 PMCID: PMC2821067 DOI: 10.1007/s00723-009-0079-2] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
The function of many proteins involves equilibria between conformational substates, and to elucidate mechanisms of function it is essential to have experimental tools to detect the presence of conformational substates and to determine the time scale of exchange between them. Site-directed spin labeling (SDSL) has the potential to serve this purpose. In proteins containing a nitroxide side chain (R1), multicomponent electron paramagnetic resonance (EPR) spectra can arise either from equilibria involving different conformational substates or rotamers of R1. To employ SDSL to uniquely identify conformational equilibria, it is thus essential to distinguish between these origins of multicomponent spectra. Here we show that this is possible based on the time scale for exchange of the nitroxide between distinct environments that give rise to multicomponent EPR spectra; rotamer exchange for R1 lies in the ≈0.1-1 μs range, while conformational exchange is at least an order of magnitude slower. The time scales of exchange events are determined by saturation recovery EPR, and in favorable cases, the exchange rate constants between substates with lifetimes of approximately 1-70 μs can be estimated by the approach.
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Affiliation(s)
- Michael D. Bridges
- Jules Stein Eye Institute and Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095-7008, USA
| | - Kálmán Hideg
- Institute of Organic and Medical Chemistry, University of Pécs, Szigeti str. 12, 7624 Pecs, Hungary
| | - Wayne L. Hubbell
- Jules Stein Eye Institute and Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095-7008, USA
- Jules Stein Eye Institute, UCLA School of Medicine, Los Angeles, CA 90095-7008, USA
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Xue Y, Podkorytov IS, Rao DK, Benjamin N, Sun H, Skrynnikov NR. Paramagnetic relaxation enhancements in unfolded proteins: theory and application to drkN SH3 domain. Protein Sci 2009; 18:1401-24. [PMID: 19544584 DOI: 10.1002/pro.153] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Site-directed spin labeling in combination with paramagnetic relaxation enhancement (PRE) measurements is one of the most promising techniques for studying unfolded proteins. Since the pioneering work of Gillespie and Shortle (J Mol Biol 1997;268:158), PRE data from unfolded proteins have been interpreted using the theory that was originally developed for rotational spin relaxation. At the same time, it can be readily recognized that the relative motion of the paramagnetic tag attached to the peptide chain and the reporter spin such as (1)H(N) is best described as a translation. With this notion in mind, we developed a number of models for the PRE effect in unfolded proteins: (i) mutual diffusion of the two tethered spheres, (ii) mutual diffusion of the two tethered spheres subject to a harmonic potential, (iii) mutual diffusion of the two tethered spheres subject to a simulated mean-force potential (Smoluchowski equation); (iv) explicit-atom molecular dynamics simulation. The new models were used to predict the dependences of the PRE rates on the (1)H(N) residue number and static magnetic field strength; the results are appreciably different from the Gillespie-Shortle model. At the same time, the Gillespie-Shortle approach is expected to be generally adequate if the goal is to reconstruct the distance distributions between (1)H(N) spins and the paramagnetic center (provided that the characteristic correlation time is known with a reasonable accuracy). The theory has been tested by measuring the PRE rates in three spin-labeled mutants of the drkN SH3 domain in 2M guanidinium chloride. Two modifications introduced into the measurement scheme-using a reference compound to calibrate the signals from the two samples (oxidized and reduced) and using peak volumes instead of intensities to determine the PRE rates-lead to a substantial improvement in the quality of data. The PRE data from the denatured drkN SH3 are mostly consistent with the model of moderately expanded random-coil protein, although part of the data point toward a more compact structure (local hydrophobic cluster). At the same time, the radius of gyration reported by Choy et al. (J Mol Biol 2002;316:101) suggests that the protein is highly expanded. This seemingly contradictory evidence can be reconciled if one assumes that denatured drkN SH3 forms a conformational ensemble that is dominated by extended conformations, yet also contains compact (collapsed) species. Such behavior is apparently more complex than predicted by the model of a random-coil protein in good solvent/poor solvent.
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Affiliation(s)
- Yi Xue
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, USA
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Smith AL, Cekan P, Brewood GP, Okonogi TM, Alemayehu S, Hustedt EJ, Benight AS, Sigurdsson ST, Robinson BH. Conformational equilibria of bulged sites in duplex DNA studied by EPR spectroscopy. J Phys Chem B 2009; 113:2664-75. [PMID: 19708106 DOI: 10.1021/jp808260b] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Conformational flexibility in nucleic acids provides a basis for complex structures, binding, and signaling. One-base bulges directly neighboring single-base mismatches in nucleic acids can be present in a minimum of two distinct conformations, complicating the examination of the thermodynamics by calorimetry or UV-monitored melting techniques. To provide additional information about such structures, we demonstrate how electron paramagnetic resonance (EPR) active spin-labeled base analogues, base-specifically incorporated into the DNA, are monitors of the superposition of different bulge-mismatch conformations. EPR spectra provide information about the dynamic environments of the probe. This information is cast in terms of "dynamic signatures" that have an underlying basis in structural variations. By examining the changes in the equilibrium of the different states across a range of temperatures, the enthalpy and entropy of the interconversion among possible conformations can be determined. The DNA constructs with a single bulge neighboring a single-base mismatch ("bulge-mismatches") may be approximately modeled as an equilibrium between two possible conformations. This structural information provides insight into the local composition of the bulge-mismatch sequences. Experiments on the bulge-mismatches show that basepairing across the helix can be understood in terms of purine and pyrimidine interactions, rather than specific bases. Measurements of the enthalpy and entropy of formation for the bulge-mismatches by differential scanning calorimetry and UV-monitored melting confirm that the formation of bulge-mismatches is in fact more complicated than a simple two-state process, consistent with the base-specific spectral data that bulge-mismatches exist in multiple conformations in the premelting temperature region. We find that the calculations with the nearest-neighbor (NN) model for the two likely conformations do not correlate well with the populations of structures and thermodynamic parameters inferred from the base-specific EPR dynamics probe. We report that the base-specific spin probes are able to identify a bistable, temperature dependent, switching between conformations for a particular complex bulged construct.
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Affiliation(s)
- Alyssa L Smith
- Department of Chemistry, University of Washington, Box 351700 Bagley Hall, Seattle, Washington 98195-1700, USA
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40
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Kathirvelu V, Sato H, Eaton SS, Eaton GR. Electron spin relaxation rates for semiquinones between 25 and 295K in glass-forming solvents. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2009; 198:111-120. [PMID: 19223213 PMCID: PMC2757793 DOI: 10.1016/j.jmr.2009.01.026] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/16/2008] [Revised: 01/13/2009] [Accepted: 01/22/2009] [Indexed: 05/27/2023]
Abstract
Electron spin lattice relaxation rates for five semiquinones (2,5-di-t-butyl-1,4-benzosemiquinone, 2,5-di-t-amyl-1,4-benzosemiquinone, 2,5-di-phenyl-1,4-benzosemiquinone, 2,6-di-t-butyl-1,4-benzosemiquinone, tetrahydroxy-1,4-benzosemiquione) were studied by long-pulse saturation recovery EPR in 1:4 glycerol:ethanol, 1:1 glycerol:ethanol, and triethanolamine between 25 and 295K. Although the dominant process changes with temperature, relaxation rates vary smoothly with temperature, even near the glass transition temperatures, and could be modeled as the sum of contributions that have the temperature dependence that is predicted for the direct, Raman, local mode and tumbling-dependent processes. At 85K, which is in a temperature range where the Raman process dominates, relaxation rates along the g(xx) (g approximately 2.006) and g(yy) (g approximately 2.005) axes are about 2.7-1.5 times faster than along the g(zz) axis (g=2.0023). In highly viscous triethanolamine, contributions from tumbling-dependent processes are negligible. At temperatures above 100K relaxation rates in triethanolamine are unchanged between X-band (9.5GHz) and Q-band (34GHz), so the process that dominates in this temperature interval was assigned as a local mode rather than a thermally activated process. Because the largest proton hyperfine couplings are only 2.2G, spin rotation makes a larger contribution than tumbling-dependent modulation of hyperfine anisotropy. Since g anisotropy is small, tumbling-dependent modulation of g anisotropy makes a smaller contribution than spin rotation at X-band. Although there was negligible impact of methyl rotation on T(1), rotation of t-butyl or t-amyl methyl groups enhances spin echo dephasing between 85 and 150K.
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Affiliation(s)
| | | | - Sandra S. Eaton
- Corresponding author: Professor Sandra S. Eaton, Department of Chemistry and Biochemistry, University of Denver Denver, CO 80208, 303-871-3102, Fax: 303-871-2254,
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Sezer D, Gafurov M, Prandolini MJ, Denysenkov VP, Prisner TF. Dynamic nuclear polarization of water by a nitroxide radical: rigorous treatment of the electron spin saturation and comparison with experiments at 9.2 Tesla. Phys Chem Chem Phys 2009; 11:6638-53. [DOI: 10.1039/b906719c] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Kathirvelu V, Eaton GR, Eaton SS. Impact of Chlorine Substitution on Spin Lattice Relaxation of Triarylmethyl and 1,4-Benzosemiquinone Radicals in Glass-forming Solvents between 25 and 295 K. APPLIED MAGNETIC RESONANCE 2009; 37:649. [PMID: 20126423 PMCID: PMC2814433 DOI: 10.1007/s00723-009-0086-3] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
Spin-lattice relaxation rates measured by long-pulse saturation recovery in glassy solvents for chlorinated aromatic radicals: perchlorotriphenylmethyl radical, 2,5-dichloro-3,6-dihydroxy-1,4-benzosemiquinone, and tetrachloro-1,4-benzosemiquinone, were compared with relaxation rates for non-chlorinated analogs. The impact of the quadrupolar chlorines is small, and less than the effects of changing the rigidity of the glass. The temperature dependence of relaxation rates below the glass transition temperature could be modeled as the sum of contributions from the direct, Raman, and local mode processes.
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Affiliation(s)
- Velavan Kathirvelu
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208
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Sarewicz M, Borek A, Daldal F, Froncisz W, Osyczka A. Demonstration of short-lived complexes of cytochrome c with cytochrome bc1 by EPR spectroscopy: implications for the mechanism of interprotein electron transfer. J Biol Chem 2008; 283:24826-36. [PMID: 18617515 PMCID: PMC2529009 DOI: 10.1074/jbc.m802174200] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2008] [Revised: 07/08/2008] [Indexed: 11/18/2022] Open
Abstract
One of the steps of a common pathway for biological energy conversion involves electron transfer between cytochrome c and cytochrome bc1. To clarify the mechanism of this reaction, we examined the structural association of those two proteins using the electron transfer-independent electron paramagnetic resonance (EPR) techniques. Drawing on the differences in the continuous wave EPR spectra and saturation recoveries of spin-labeled bacterial and mitochondrial cytochromes c recorded in the absence and presence of bacterial cytochrome bc1, we have exposed a time scale of dynamic equilibrium between the bound and the free state of cytochrome c at various ionic strengths. Our data show a successive decrease of the bound cytochrome c fraction as the ionic strength increases, with a limit of approximately 120 mm NaCl above which essentially no bound cytochrome c can be detected by EPR. This limit does not apply to all of the interactions of cytochrome c with cytochrome bc1 because the cytochrome bc1 enzymatic activity remained high over a much wider range of ionic strengths. We concluded that EPR monitors just the tightly bound state of the association and that an averaged lifetime of this state decreases from over 100 micros at low ionic strength to less than 400 ns at an ionic strength above 120 mm. This suggests that at physiological ionic strength, the tightly bound complex on average lasts less than the time needed for a single electron exchange between hemes c and c1, indicating that productive electron transfer requires several collisions of the two molecules. This is consistent with an early idea of diffusion-coupled reactions that link the soluble electron carriers with the membranous complexes, which, we believe, provides a robust means of regulating electron flow through these complexes.
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Affiliation(s)
- Marcin Sarewicz
- Department of Biophysics, Faculty of
Biochemistry, Biophysics, and Biotechnology, Jagiellonian University, 30-387
Kraków, Poland and the Department of
Biology, Plant Science Institute, University of Pennsylvania, Philadelphia,
Pennsylvania 19104
| | - Arkadiusz Borek
- Department of Biophysics, Faculty of
Biochemistry, Biophysics, and Biotechnology, Jagiellonian University, 30-387
Kraków, Poland and the Department of
Biology, Plant Science Institute, University of Pennsylvania, Philadelphia,
Pennsylvania 19104
| | - Fevzi Daldal
- Department of Biophysics, Faculty of
Biochemistry, Biophysics, and Biotechnology, Jagiellonian University, 30-387
Kraków, Poland and the Department of
Biology, Plant Science Institute, University of Pennsylvania, Philadelphia,
Pennsylvania 19104
| | - Wojciech Froncisz
- Department of Biophysics, Faculty of
Biochemistry, Biophysics, and Biotechnology, Jagiellonian University, 30-387
Kraków, Poland and the Department of
Biology, Plant Science Institute, University of Pennsylvania, Philadelphia,
Pennsylvania 19104
| | - Artur Osyczka
- Department of Biophysics, Faculty of
Biochemistry, Biophysics, and Biotechnology, Jagiellonian University, 30-387
Kraków, Poland and the Department of
Biology, Plant Science Institute, University of Pennsylvania, Philadelphia,
Pennsylvania 19104
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Froncisz W, Camenisch TG, Ratke JJ, Anderson JR, Subczynski WK, Strangeway RA, Sidabras JW, Hyde JS. Saturation recovery EPR and ELDOR at W-band for spin labels. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2008; 193:297-304. [PMID: 18547848 PMCID: PMC2561891 DOI: 10.1016/j.jmr.2008.05.008] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/07/2007] [Revised: 04/30/2008] [Accepted: 05/14/2008] [Indexed: 05/03/2023]
Abstract
A reference arm W-band (94 GHz) microwave bridge with two sample-irradiation arms for saturation recovery (SR) EPR and ELDOR experiments is described. Frequencies in each arm are derived from 2 GHz synthesizers that have a common time-base and are translated to 94 GHz in steps of 33 and 59 GHz. Intended applications are to nitroxide radical spin labels and spin probes in the liquid phase. An enabling technology is the use of a W-band loop-gap resonator (LGR) [J.W. Sidabras, R.R. Mett, W. Froncisz, T.G. Camenisch, J.R. Anderson, J.S. Hyde, Multipurpose EPR loop-gap resonator and cylindrical TE(011) cavity for aqueous samples at 94 GHz, Rev. Sci. Instrum. 78 (2007) 034701]. The high efficiency parameter (8.2 GW(-1/2) with sample) permits the saturating pump pulse level to be just 5 mW or less. Applications of SR EPR and ELDOR to the hydrophilic spin labels 3-carbamoyl-2,2,5,5-tetra-methyl-3-pyrroline-1-yloxyl (CTPO) and 2,2,6,6,-tetramethyl-4-piperidone-1-oxyl (TEMPONE) are described in detail. In the SR ELDOR experiment, nitrogen nuclear relaxation as well as Heisenberg exchange transfer saturation from pumped to observed hyperfine transitions. SR ELDOR was found to be an essential method for measurements of saturation transfer rates for small molecules such as TEMPONE. Free induction decay (FID) signals for small nitroxides at W-band are also reported. Results are compared with multifrequency measurements of T(1e) previously reported for these molecules in the range of 2-35 GHz [J.S. Hyde, J.-J. Yin, W.K. Subczynski, T.G. Camenisch, J.J. Ratke, W. Froncisz, Spin label EPR T(1) values using saturation recovery from 2 to 35 GHz. J. Phys. Chem. B 108 (2004) 9524-9529]. The values of T(1e) decrease at 94 GHz relative to values at 35 GHz.
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Affiliation(s)
- Wojciech Froncisz
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI, USA
- Jagiellonian University, Krakow, Poland
| | | | - Joseph J. Ratke
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI, USA
| | - James R. Anderson
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI, USA
| | | | - Robert A. Strangeway
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI, USA
- Milwaukee School of Engineering, Milwaukee, WI, USA
| | - Jason W. Sidabras
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI, USA
| | - James S. Hyde
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI, USA
- Author to whom correspondence should be addressed: James S. Hyde, Ph.D., Department of Biophysics, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226-0509, Phone: (414) 456-4005, Fax: (414) 456-6512, E-mail:
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Smith AL, Cekan P, Rangel DP, Sigurdsson ST, Mailer C, Robinson BH. Theory for Spin−Lattice Relaxation of Spin Probes on Weakly Deformable DNA. J Phys Chem B 2008; 112:9219-36. [DOI: 10.1021/jp7111704] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Alyssa L. Smith
- Department of Chemistry, University of Washington, Seattle, Washington, Science Institute, University of Iceland, Reykjavik, Iceland, and Department of Radiology, University of Chicago, Chicago, Illinois
| | - Pavol Cekan
- Department of Chemistry, University of Washington, Seattle, Washington, Science Institute, University of Iceland, Reykjavik, Iceland, and Department of Radiology, University of Chicago, Chicago, Illinois
| | - David P. Rangel
- Department of Chemistry, University of Washington, Seattle, Washington, Science Institute, University of Iceland, Reykjavik, Iceland, and Department of Radiology, University of Chicago, Chicago, Illinois
| | - Snorri Th. Sigurdsson
- Department of Chemistry, University of Washington, Seattle, Washington, Science Institute, University of Iceland, Reykjavik, Iceland, and Department of Radiology, University of Chicago, Chicago, Illinois
| | - Colin Mailer
- Department of Chemistry, University of Washington, Seattle, Washington, Science Institute, University of Iceland, Reykjavik, Iceland, and Department of Radiology, University of Chicago, Chicago, Illinois
| | - Bruce H. Robinson
- Department of Chemistry, University of Washington, Seattle, Washington, Science Institute, University of Iceland, Reykjavik, Iceland, and Department of Radiology, University of Chicago, Chicago, Illinois
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Sato H, Bottle SE, Blinco JP, Micallef AS, Eaton GR, Eaton SS. Electron spin-lattice relaxation of nitroxyl radicals in temperature ranges that span glassy solutions to low-viscosity liquids. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2008; 191:66-77. [PMID: 18166493 PMCID: PMC2671210 DOI: 10.1016/j.jmr.2007.12.003] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/28/2007] [Revised: 12/07/2007] [Accepted: 12/07/2007] [Indexed: 05/12/2023]
Abstract
Electron spin-lattice relaxation rates, 1/T1, at X-band of nitroxyl radicals (4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl, 4-oxo-2,2,6,6-tetramethylpiperidin-1-oxyl, 3-carbamoyl-2,2,5,5-tetramethylpyrrolidin-1-oxyl and 3-carbamoyl-2,2,5,5-tetramethylpyrrolin-1-oxyl) in glass-forming solvents (decalin, glycerol, 3-methylpentane, o-terphenyl, 1-propanol, sorbitol, sucrose octaacetate, and 1:1 water:glycerol) at temperatures between 100 and 300K were measured by long-pulse saturation recovery to investigate the relaxation processes in slow-to-fast tumbling regimes. A subset of samples was also studied at lower temperatures or at Q-band. Tumbling correlation times were calculated from continuous wave lineshapes. Temperature dependence and isotope substitution (2H and 15N) were used to distinguish the contributions of various processes. Below about 100K relaxation is dominated by the Raman process. At higher temperatures, but below the glass transition temperature, a local mode process makes significant contributions. Above the glass transition temperature, increased rates of molecular tumbling modulate nuclear hyperfine and g anisotropy. The contribution from spin rotation is very small. Relaxation rates at X-band and Q-band are similar. The dependence of 1/T1 on tumbling correlation times fits better with the Cole-Davidson spectral density function than with the Bloembergen-Purcell-Pound model.
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Affiliation(s)
- Hideo Sato
- Department of Chemistry and Biochemistry, University of Denver, Denver, Colorado 80208
| | - Steven E. Bottle
- ARC Centre of Excellence for Free Radical Chemistry and Biotechnology, School of Physical and Chemical Sciences, Queensland University of Technology, GPO Box 2434 Q4001, Australia
| | - James P. Blinco
- ARC Centre of Excellence for Free Radical Chemistry and Biotechnology, School of Physical and Chemical Sciences, Queensland University of Technology, GPO Box 2434 Q4001, Australia
| | - Aaron S. Micallef
- ARC Centre of Excellence for Free Radical Chemistry and Biotechnology, School of Physical and Chemical Sciences, Queensland University of Technology, GPO Box 2434 Q4001, Australia
| | - Gareth R. Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, Colorado 80208
| | - Sandra S. Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, Colorado 80208
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