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Stimson L, Dong L, Karttunen M, Wisniewska A, Dutka M, Róg T. Stearic Acid Spin Labels in Lipid Bilayers: Insight through Atomistic Simulations. J Phys Chem B 2007; 111:12447-53. [DOI: 10.1021/jp0746796] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Lorna Stimson
- Laboratory of Physics, Helsinki University of Technology, Finland, Department of Applied Mathematics, The University of Western Ontario, London (ON), Canada, Department of Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Kraków, Poland, and Biophysics and Statistical Mechanics Group, Department of Electrical and Communication Engineering, Helsinki University of Technology, Finland
| | - Lei Dong
- Laboratory of Physics, Helsinki University of Technology, Finland, Department of Applied Mathematics, The University of Western Ontario, London (ON), Canada, Department of Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Kraków, Poland, and Biophysics and Statistical Mechanics Group, Department of Electrical and Communication Engineering, Helsinki University of Technology, Finland
| | - Mikko Karttunen
- Laboratory of Physics, Helsinki University of Technology, Finland, Department of Applied Mathematics, The University of Western Ontario, London (ON), Canada, Department of Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Kraków, Poland, and Biophysics and Statistical Mechanics Group, Department of Electrical and Communication Engineering, Helsinki University of Technology, Finland
| | - Anna Wisniewska
- Laboratory of Physics, Helsinki University of Technology, Finland, Department of Applied Mathematics, The University of Western Ontario, London (ON), Canada, Department of Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Kraków, Poland, and Biophysics and Statistical Mechanics Group, Department of Electrical and Communication Engineering, Helsinki University of Technology, Finland
| | - Małgorzata Dutka
- Laboratory of Physics, Helsinki University of Technology, Finland, Department of Applied Mathematics, The University of Western Ontario, London (ON), Canada, Department of Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Kraków, Poland, and Biophysics and Statistical Mechanics Group, Department of Electrical and Communication Engineering, Helsinki University of Technology, Finland
| | - Tomasz Róg
- Laboratory of Physics, Helsinki University of Technology, Finland, Department of Applied Mathematics, The University of Western Ontario, London (ON), Canada, Department of Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Kraków, Poland, and Biophysics and Statistical Mechanics Group, Department of Electrical and Communication Engineering, Helsinki University of Technology, Finland
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Widomska J, Raguz M, Subczynski WK. Oxygen permeability of the lipid bilayer membrane made of calf lens lipids. BIOCHIMICA ET BIOPHYSICA ACTA 2007; 1768:2635-45. [PMID: 17662231 PMCID: PMC2093700 DOI: 10.1016/j.bbamem.2007.06.018] [Citation(s) in RCA: 94] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/07/2007] [Revised: 06/14/2007] [Accepted: 06/18/2007] [Indexed: 11/15/2022]
Abstract
The oxygen permeability coefficient across the membrane made of the total lipid extract from the plasma membrane of calf lens was estimated from the profile of the oxygen transport parameter (local oxygen diffusion-concentration product) and compared with those estimated for membranes made of an equimolar 1-palmitoyl-2-oleoylphosphatidylcholine/cholesterol (POPC/Chol) mixture and of pure POPC. Profiles of the oxygen transport parameter were obtained by observing the collision of molecular oxygen with nitroxide radical spin labels placed at different depths in the membrane using the saturation-recovery EPR technique and were published by us earlier (J. Widomska, M. Raguz, J. Dillon, E. R. Gaillard, W. K. Subczynski, Biochim. Biophys. Acta. 1768 (2007) 1454-1465). At 35 degrees C, the estimated oxygen permeability coefficients were 51.3, 49.7, and 157.4 cm/s for lens lipid, POPC/Chol, and POPC membranes, respectively (compared with 53.3 cm/s for a water layer with the same thickness as a membrane). Membrane permeability significantly decreases at lower temperatures. In the lens lipid membrane, resistance to the oxygen transport is located in and near the polar headgroup region of the membrane to the depth of the ninth carbon, which is approximately where the steroid-ring structure of cholesterol reaches into the membrane. In the central region of the membrane, oxygen transport is enhanced, significantly exceeding that in bulk water. It is concluded that the high level of cholesterol in lens lipids is responsible for these unique membrane properties.
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Affiliation(s)
- Justyna Widomska
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, Wisconsin 53226, USA
| | - Marija Raguz
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, Wisconsin 53226, USA
| | - Witold K. Subczynski
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, Wisconsin 53226, USA
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Widomska J, Raguz M, Dillon J, Gaillard ER, Subczynski WK. Physical properties of the lipid bilayer membrane made of calf lens lipids: EPR spin labeling studies. BIOCHIMICA ET BIOPHYSICA ACTA 2007; 1768:1454-65. [PMID: 17451639 PMCID: PMC2041941 DOI: 10.1016/j.bbamem.2007.03.007] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/31/2006] [Revised: 03/09/2007] [Accepted: 03/13/2007] [Indexed: 11/23/2022]
Abstract
The physical properties of a membrane derived from the total lipids of a calf lens were investigated using EPR spin labeling and were compared with the properties of membranes made of an equimolar 1-palmitoyl-2-oleoylphosphatidylcholine/cholesterol (POPC/Chol) mixture and of pure POPC. Conventional EPR spectra and saturation-recovery curves show that spin labels detect a single homogenous environment in all three membranes. Profiles of the order parameter, hydrophobicity, and oxygen transport parameter are practically identical in lens lipid and POPC/Chol membranes, but differ drastically from profiles in pure POPC membranes. In both lens lipid and POPC/Chol membranes, the lipids are strongly immobilized at all depths, which is in contrast to the high fluidity of the POPC membrane. Hydrophobicity and oxygen transport parameter profiles in lens lipid and POPC/Chol membranes have a rectangular shape with an abrupt change between the C9 and C10 positions, which is approximately where the steroid ring structure of cholesterol reaches into the membrane. At this position, hydrophobicity increases from the level of methanol to the level of hexane, and the oxygen transport parameter increases by a factor of 2-3. These profiles in POPC membranes are bell-shaped. It is concluded that the high level of cholesterol in lens lipids makes the membrane stable, immobile, and impermeable to both polar and nonpolar molecules.
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Affiliation(s)
- Justyna Widomska
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, Wisconsin 53226, USA
| | - Marija Raguz
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, Wisconsin 53226, USA
| | - James Dillon
- Department of Ophthalmology, Columbia University, New York, New York 10032, USA
| | - Elizabeth R. Gaillard
- Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, Illinois, 60115, USA
| | - Witold K. Subczynski
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, Wisconsin 53226, USA
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Subczynski WK, Widomska J, Wisniewska A, Kusumi A. Saturation-recovery electron paramagnetic resonance discrimination by oxygen transport (DOT) method for characterizing membrane domains. Methods Mol Biol 2007; 398:143-57. [PMID: 18214379 DOI: 10.1007/978-1-59745-513-8_11] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
The discrimination by oxygen transport (DOT) method is a dual-probe saturation-recovery electron paramagnetic resonance approach in which the observable parameter is the spin-lattice relaxation time (T1) of lipid spin labels, and the measured value is the bimolecular collision rate between molecular oxygen and the nitroxide moiety of spin labels. This method has proven to be extremely sensitive to changes in the local oxygen diffusion-concentration product (around the nitroxide moiety) because of the long T1 of lipid spin labels (1-10 micros) and also because molecular oxygen is a unique probe molecule. Molecular oxygen is paramagnetic, small, and has the appropriate level of hydrophobicity that allows it to partition into various supramolecular structures such as different membrane domains. When located in two different membrane domains, the spin label alone most often cannot differentiate between these domains, giving very similar (indistinguishable) conventional electron paramagnetic resonance spectra and similar T1 values. However, even small differences in lipid packing in these domains will affect oxygen partitioning and oxygen diffusion, which can be easily detected by observing the different T1s from spin labels in these two locations in the presence of molecular oxygen. The DOT method allows one not only to distinguish between the different domains, but also to obtain the value of the oxygen diffusion-concentration product in these domains, which is a useful physical characteristic of the organization of lipids in domains. Profiles of the oxygen diffusion-concentration product (the oxygen transport parameter) in coexisting domains can be obtained in situ without the need for the physical separation of the two domains. Furthermore, under optimal conditions, the exchange rate of spin-labeled molecules between the two domains could be measured.
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