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Beauchemin PF, Bayly PV, Garbow JR, Schmidt JLS, Okamoto RJ, Chériet F, Périé D. Frequency-dependent shear properties of annulus fibrosus and nucleus pulposus by magnetic resonance elastography. NMR Biomed 2018; 31:e3918. [PMID: 29727498 DOI: 10.1002/nbm.3918] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/07/2017] [Revised: 12/23/2017] [Accepted: 02/15/2018] [Indexed: 05/22/2023]
Abstract
Aging and degeneration are associated with changes in mechanical properties in the intervertebral disc, generating interest in the establishment of mechanical properties as early biomarkers for the degenerative cascade. Magnetic resonance elastography (MRE) of the intervertebral disc is usually limited to the nucleus pulposus, as the annulus fibrosus is stiffer and less hydrated. The objective of this work was to adapt high-frequency needle MRE to the characterization of the shear modulus of both the nucleus pulposus and annulus fibrosus. Bovine intervertebral discs were removed from fresh oxtails and characterized by needle MRE. The needle was inserted in the center of the disc and vibrations were generated by an amplified piezoelectric actuator. MRE acquisitions were performed on a 4.7-T small-animal MR scanner using a spin echo sequence with sinusoidal motion encoding gradients. Acquisitions were repeated over a frequency range of 1000-1800 Hz. The local frequency estimation inversion algorithm was used to compute the shear modulus. Stiffness maps allowed the visualization of the soft nucleus pulposus surrounded by the stiffer annulus fibrosus surrounded by the homogeneous gel. A significant difference in shear modulus between the nucleus pulposus and annulus fibrosus, and an increase in the shear modulus with excitation frequency, were observed, in agreement with the literature. This study demonstrates that global characterization of both the nucleus pulposus and annulus fibrosus of the intervertebral disc is possible with needle MRE using a preclinical magnetic resonance imaging (MRI) scanner. MRE can be a powerful method for the mapping of the complex properties of the intervertebral disc. The developed method could be adapted for in situ use by preserving adjacent vertebrae and puncturing the side of the intervertebral disc, thereby allowing an assessment of the contribution of osmotic pressure to the mechanical behavior of the intervertebral disc.
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Affiliation(s)
- P F Beauchemin
- Mechanical Engineering, Polytechnique de Montréal, Montréal, QC, Canada
| | - P V Bayly
- Mechanical Engineering and Materials Science, Washington University in St. Louis, St. Louis, MO, USA
| | - J R Garbow
- Mallinckrodt Institute of Radiology, Washington University in St. Louis, St. Louis, MO, USA
| | - J L S Schmidt
- Mechanical Engineering and Materials Science, Washington University in St. Louis, St. Louis, MO, USA
| | - R J Okamoto
- Mechanical Engineering and Materials Science, Washington University in St. Louis, St. Louis, MO, USA
| | - F Chériet
- Mechanical Engineering, Polytechnique de Montréal, Montréal, QC, Canada
- Research Center, CHU Sainte-Justine, Montréal, QC, Canada
| | - D Périé
- Mechanical Engineering, Polytechnique de Montréal, Montréal, QC, Canada
- Research Center, CHU Sainte-Justine, Montréal, QC, Canada
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2
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Bayly PV, Garbow JR. Pre-clinical MR elastography: Principles, techniques, and applications. J Magn Reson 2018; 291:73-83. [PMID: 29705042 PMCID: PMC5943171 DOI: 10.1016/j.jmr.2018.01.004] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/15/2017] [Accepted: 01/07/2018] [Indexed: 05/09/2023]
Abstract
Magnetic resonance elastography (MRE) is a method for measuring the mechanical properties of soft tissue in vivo, non-invasively, by imaging propagating shear waves in the tissue. The speed and attenuation of waves depends on the elastic and dissipative properties of the underlying material. Tissue mechanical properties are essential for biomechanical models and simulations, and may serve as markers of disease, injury, development, or recovery. MRE is already established as a clinical technique for detecting and characterizing liver disease. The potential of MRE for diagnosing or characterizing disease in other organs, including brain, breast, and heart is an active research area. Studies involving MRE in the pre-clinical setting, in phantoms and artificial biomaterials, in the mouse, and in other mammals, are critical to the development of MRE as a robust, reliable, and useful modality.
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Affiliation(s)
- P V Bayly
- Mechanical Engineering and Materials Science, Washington University in Saint Louis, MO, USA.
| | - J R Garbow
- Radiology, Washington University School of Medicine, Saint Louis, MO, USA
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Schmidt JL, Tweten DJ, Badachhape AA, Reiter AJ, Okamoto RJ, Garbow JR, Bayly PV. Measurement of anisotropic mechanical properties in porcine brain white matter ex vivo using magnetic resonance elastography. J Mech Behav Biomed Mater 2017; 79:30-37. [PMID: 29253729 DOI: 10.1016/j.jmbbm.2017.11.045] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2017] [Revised: 11/12/2017] [Accepted: 11/27/2017] [Indexed: 02/05/2023]
Abstract
The mechanical properties of brain tissue, particularly those of white matter (WM), need to be characterized accurately for use in finite element (FE) models of brain biomechanics and traumatic brain injury (TBI). Magnetic resonance elastography (MRE) is a powerful tool for non-invasive estimation of the mechanical properties of soft tissues. While several studies involving direct mechanical tests of brain tissue have shown mechanical anisotropy, most MRE studies of brain tissue assume an isotropic model. In this study, an incompressible transversely isotropic (TI) material model parameterized by minimum shear modulus (μ2), shear anisotropy parameter (ϕ), and tensile anisotropy parameter (ζ) is applied to analyze MRE measurements of ex vivo porcine white matter (WM) brain tissue. To characterize shear anisotropy, "slow" (pure transverse) shear waves were propagated at 100, 200 and 300Hz through sections of ex vivo brain tissue including both WM and gray matter (GM). Shear waves were found to propagate with elliptical fronts, consistent with TI material behavior. Shear wave fields were also analyzed within regions of interest (ROI) to find local shear wavelengths parallel and perpendicular to fiber orientation. FE simulations of a TI material with a range of plausible shear modulus (μ2) and shear anisotropy parameters (ϕ) were run and the results were analyzed in the same fashion as the experimental case. Parameters of the FE simulations which most closely matched each experiment were taken to represent the mechanical properties of that particular sample. Using this approach, WM in the ex vivo porcine brain was found to be mildly anisotropic in shear with estimates of minimum shear modulus (actuation frequencies listed in parenthesis): μ2= 1.04 ± 0.12 kPa (at 100Hz), μ2= 1.94 ± 0.29 kPa (at 200Hz), and μ2= 2.88 ± 0.34 kPa (at 300Hz) and corresponding shear anisotropy factors of ϕ= 0.27 ± 0.09 (at 100Hz), ϕ= 0.29 ± 0.14 (at 200Hz) and ϕ= 0.34 ± 0.13 (at 300Hz). Future MRE studies will focus on tensile anisotropy, which will require both slow and fast shear waves for accurate estimation.
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Affiliation(s)
- J L Schmidt
- Mechanical Engineering and Materials Science, Washington University in Saint Louis, MO 63130, United States.
| | - D J Tweten
- Mechanical Engineering and Materials Science, Washington University in Saint Louis, MO 63130, United States
| | - A A Badachhape
- Biomedical Engineering, Washington University in Saint Louis, MO 63130, United States
| | - A J Reiter
- Mechanical Engineering and Materials Science, Washington University in Saint Louis, MO 63130, United States
| | - R J Okamoto
- Mechanical Engineering and Materials Science, Washington University in Saint Louis, MO 63130, United States
| | - J R Garbow
- Radiology, Washington University in Saint Louis, MO 63130, United States
| | - P V Bayly
- Mechanical Engineering and Materials Science, Washington University in Saint Louis, MO 63130, United States; Biomedical Engineering, Washington University in Saint Louis, MO 63130, United States
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Feng Y, Clayton EH, Okamoto RJ, Engelbach J, Bayly PV, Garbow JR. A longitudinal magnetic resonance elastography study of murine brain tumors following radiation therapy. Phys Med Biol 2016; 61:6121-31. [PMID: 27461395 DOI: 10.1088/0031-9155/61/16/6121] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
An accurate and noninvasive method for assessing treatment response following radiotherapy is needed for both treatment monitoring and planning. Measurement of solid tumor volume alone is not sufficient for reliable early detection of therapeutic response, since changes in physiological and/or biomechanical properties can precede tumor volume change following therapy. In this study, we use magnetic resonance elastography to evaluate the treatment effect after radiotherapy in a murine brain tumor model. Shear modulus was calculated and compared between the delineated tumor region of interest (ROI) and its contralateral, mirrored counterpart. We also compared the shear modulus from both the irradiated and non-irradiated tumor and mirror ROIs longitudinally, sampling four time points spanning 9-19 d post tumor implant. Results showed that the tumor ROI had a lower shear modulus than that of the mirror ROI, independent of radiation. The shear modulus of the tumor ROI decreased over time for both the treated and untreated groups. By contrast, the shear modulus of the mirror ROI appeared to be relatively constant for the treated group, while an increasing trend was observed for the untreated group. The results provide insights into the tumor properties after radiation treatment and demonstrate the potential of using the mechanical properties of the tumor as a biomarker. In future studies, more closely spaced time points will be employed for detailed analysis of the radiation effect.
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Affiliation(s)
- Y Feng
- School of Mechanical and Electronic Engineering, Soochow University, Suzhou, Jiangsu, People's Republic of China. Robotics and Microsystems Center, Soochow University, Suzhou, Jiangsu, People's Republic of China. School of Computer Science and Engineering, Soochow University, Suzhou, Jiangsu, People's Republic of China
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Schmidt JL, Tweten DJ, Benegal AN, Walker CH, Portnoi TE, Okamoto RJ, Garbow JR, Bayly PV. Magnetic resonance elastography of slow and fast shear waves illuminates differences in shear and tensile moduli in anisotropic tissue. J Biomech 2016; 49:1042-1049. [PMID: 26920505 DOI: 10.1016/j.jbiomech.2016.02.018] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2015] [Revised: 02/06/2016] [Accepted: 02/08/2016] [Indexed: 12/13/2022]
Abstract
Mechanical anisotropy is an important property of fibrous tissues; for example, the anisotropic mechanical properties of brain white matter may play a key role in the mechanics of traumatic brain injury (TBI). The simplest anisotropic material model for small deformations of soft tissue is a nearly incompressible, transversely isotropic (ITI) material characterized by three parameters: minimum shear modulus (µ), shear anisotropy (ϕ=µ1µ-1) and tensile anisotropy (ζ=E1E2-1). These parameters can be determined using magnetic resonance elastography (MRE) to visualize shear waves, if the angle between the shear-wave propagation direction and fiber direction is known. Most MRE studies assume isotropic material models with a single shear (µ) or tensile (E) modulus. In this study, two types of shear waves, "fast" and "slow", were analyzed for a given propagation direction to estimate anisotropic parameters µ, ϕ, and ζ in two fibrous soft materials: turkey breast ex vivo and aligned fibrin gels. As expected, the speed of slow shear waves depended on the angle between fiber direction and propagation direction. Fast shear waves were observed when the deformations due to wave motion induced stretch in the fiber direction. Finally, MRE estimates of anisotropic mechanical properties in turkey breast were compared to estimates from direct mechanical tests.
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Affiliation(s)
- J L Schmidt
- Mechanical Engineering and Materials Science, Washington University in St. Louis, United States
| | - D J Tweten
- Mechanical Engineering and Materials Science, Washington University in St. Louis, United States
| | - A N Benegal
- Biomedical Engineering, Washington University in St. Louis, United States
| | - C H Walker
- Biomedical Engineering, Washington University in St. Louis, United States
| | - T E Portnoi
- Electrical Engineering, Massachusetts Institute of Technology, United States
| | - R J Okamoto
- Mechanical Engineering and Materials Science, Washington University in St. Louis, United States
| | - J R Garbow
- Biomedical Magnetic Resonance Laboratory, Radiology, Washington University in St. Louis, United States
| | - P V Bayly
- Mechanical Engineering and Materials Science, Washington University in St. Louis, United States; Biomedical Engineering, Washington University in St. Louis, United States.
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6
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Abstract
The placenta performs a wide range of physiological functions; insufficiencies in these functions may result in a variety of severe prenatal and postnatal syndromes with long-term negative impacts on human adult health. Recent advances in magnetic resonance imaging (MRI) studies of placental function, in both animal models and humans, have contributed significantly to our understanding of placental structure, blood flow, oxygenation status, and metabolic profile, and have provided important insights into pregnancy complications.
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Affiliation(s)
- R Avni
- Department of Biological Regulation, Weizmann Institute of Science, Rehovot 76100, Israel
| | - M Neeman
- Department of Biological Regulation, Weizmann Institute of Science, Rehovot 76100, Israel.
| | - J R Garbow
- Biomedical MR Laboratory, Mallinckrodt Institute of Radiology, Washington University, St. Louis, Missouri, United States.
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Anderson JR, Ackerman JJH, Garbow JR. Semipermeable Hollow Fiber Phantoms for Development and Validation of Perfusion-Sensitive MR Methods and Signal Models. Concepts Magn Reson Part B Magn Reson Eng 2011; 39B:149-158. [PMID: 26167136 PMCID: PMC4497530 DOI: 10.1002/cmr.b.20202] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Two semipermeable, hollow fiber phantoms for the validation of perfusion-sensitive magnetic resonance methods and signal models are described. Semipermeable hollow fibers harvested from a standard commercial hemodialysis cartridge serve to mimic tissue capillary function. Flow of aqueous media through the fiber lumen is achieved with a laboratory-grade peristaltic pump. Diffusion of water and solute species (e.g., Gd-based contrast agent) occurs across the fiber wall, allowing exchange between the lumen and the extralumenal space. Phantom design attributes include: i) small physical size, ii) easy and low-cost construction, iii) definable compartment volumes, and iv) experimental control over media content and flow rate.
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Affiliation(s)
- J R Anderson
- Department of Chemistry, Washington University, 1 Brookings Drive, St. Louis, MO 63130
| | - J J H Ackerman
- Department of Chemistry, Washington University, 1 Brookings Drive, St. Louis, MO 63130 ; Department of Radiology, Washington University, 1 Brookings Drive, St. Louis, MO 63130 ; Department of Internal Medicine, Washington University, 1 Brookings Drive, St. Louis, MO 63130
| | - J R Garbow
- Department of Radiology, Washington University, 1 Brookings Drive, St. Louis, MO 63130
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Anderson JR, Ye Q, Neil JJ, Ackerman JJH, Garbow JR. Diffusion effects on longitudinal relaxation in poorly mixed compartments. J Magn Reson 2011; 211:30-36. [PMID: 21524595 PMCID: PMC3114270 DOI: 10.1016/j.jmr.2011.03.018] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/13/2011] [Revised: 03/25/2011] [Accepted: 03/28/2011] [Indexed: 05/30/2023]
Abstract
Diffusion of spins between physical or virtual, communicating compartments having different states of longitudinal magnetization leads to diffusion-driven longitudinal relaxation. Herein, in two model systems, the effects of diffusion-driven longitudinal relaxation are explored experimentally and analyzed quantitatively. In the first case, longitudinal relaxation in a single slice of a water phantom is monitored spectroscopically as a function of slice thickness. In the second case, mimicking vascular flow/diffusion effects, longitudinal relaxation is monitored in a two-compartment, semi-permeable fiber phantom. In both cases, apparent longitudinal relaxation, though clearly multi-exponential, is well-modeled as bi-exponential.
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Affiliation(s)
- J R Anderson
- Department of Chemistry, Washington University, St. Louis, MO 63130, USA
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9
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Abstract
Viscoelastic properties of mouse brain tissue were estimated non-invasively, in vivo, using magnetic resonance elastography (MRE) at 4.7 T to measure the dispersive properties of induced shear waves. Key features of this study include (i) the development and application of a novel MR-compatible actuation system which transmits vibratory motion into the brain through an incisor bar, and (ii) the investigation of the mechanical properties of brain tissue over a 1200 Hz bandwidth from 600-1800 Hz. Displacement fields due to propagating shear waves were measured during continuous, harmonic excitation of the skull. This protocol enabled characterization of the true steady-state patterns of shear wave propagation. Analysis of displacement fields obtained at different frequencies indicates that the viscoelastic properties of mouse brain tissue depend strongly on frequency. The average storage modulus (G') increased from approximately 1.6 to 8 kPa over this range; average loss modulus (G″) increased from approximately 1 to 3 kPa. Both moduli were well approximated by a power-law relationship over this frequency range. MRE may be a valuable addition to studies of disease in murine models, and to pre-clinical evaluations of therapies. Quantitative measurements of the viscoelastic parameters of brain tissue at high frequencies are also valuable for modeling and simulation of traumatic brain injury.
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Affiliation(s)
- E H Clayton
- Department of Mechanical Engineering and Materials Science, Washington University in St Louis, 1 Brookings Drive, Campus Box 1185, Saint Louis, MO 63130, USA.
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10
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Jost SC, Collins L, Travers S, Piwnica-Worms D, Garbow JR. Measuring brain tumor growth: combined bioluminescence imaging-magnetic resonance imaging strategy. Mol Imaging 2009; 8:245-253. [PMID: 19796602 PMCID: PMC3831362] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/28/2023] Open
Abstract
Small-animal tumor models are essential for developing translational therapeutic strategies in oncology research, with imaging having an increasingly important role. Magnetic resonance imaging (MRI) offers tumor localization, volumetric measurement, and the potential for advanced physiologic imaging but is less well suited to high-throughput studies and has limited capacity to assess early tumor growth. Bioluminescence imaging (BLI) identifies tumors early, monitors tumor growth, and efficiently measures response to therapeutic intervention. Generally, BLI signals have been found to correlate well with magnetic resonance measurements of tumor volume. However, in our studies of small-animal models of malignant brain tumors, we have observed specific instances in which BLI data do not correlate with corresponding MRIs. These observations led us to hypothesize that use of BLI and MRI together, rather than in isolation, would allow more effective and efficient measures of tumor growth in preclinical studies. Herein we describe combining BLI and MRI studies to characterize tumor growth in a mouse model of glioblastoma. The results led us to suggest a cost-effective, multimodality strategy for selecting cohorts of animals with similar tumor growth patterns that improves the accuracy of longitudinal in vivo measurements of tumor growth and treatment response in preclinical therapeutic studies.
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Affiliation(s)
- S. C. Jost
- Department of Neurosurgery, Washington University School of Medicine, St. Louis, MO 63110
| | - L. Collins
- Molecular Imaging Center, Department of Radiology, and Department of Developmental Biology, Washington University School of Medicine, St. Louis, MO 63110
| | - S. Travers
- Department of Neurosurgery, Washington University School of Medicine, St. Louis, MO 63110
- Biomedical MR Laboratory, Department of Radiology, Washington University School of Medicine, St. Louis, MO 63110
| | - D. Piwnica-Worms
- Molecular Imaging Center, Department of Radiology, and Department of Developmental Biology, Washington University School of Medicine, St. Louis, MO 63110
| | - J. R. Garbow
- Biomedical MR Laboratory, Department of Radiology, Washington University School of Medicine, St. Louis, MO 63110
- Alvin J Siteman Cancer Center, Washington University School of Medicine, St. Louis, MO 63110
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Abstract
Improvements in noninvasive imaging modalities are crucial for preoperative in vivo assessments of liver condition and potential for regeneration after liver resection for removal of liver tumors. To that end, an MRI study of liver regeneration in mice following partial hepatectomy is described and validated. Hepatic volumes were accurately measured from contrast-enhanced, gradient-echo images of the liver. Regeneration curves were constructed for a series of mice (N = 6) from a longitudinal MR study, with images collected 1, 2, 3, 4, 5, and 9 days following surgery. We validated the MR method by correlating serial MR-measured volumes with liver wet weight. The success of this method will enable future studies to better elucidate the factors that affect regeneration, and help to optimize the timing and dosing of chemotherapeutics to minimize their deleterious effects on liver regeneration.
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Affiliation(s)
- J R Garbow
- Department of Chemistry, Washington University, St. Louis, Missouri 63110, USA.
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12
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Abstract
A magnetic resonance spectroscopy (MRS) procedure for in vivo measurement of lipid levels in mouse liver is described and validated. The method uses respiratory-gated, localized spectroscopy to collect proton spectra from voxels within the mouse liver. Bayesian probability theory analysis of these spectra allows the relative intensities of the lipid and water resonances within the liver to be accurately measured. All spectral data were corrected for measured spin-spin relaxation. A total of 48 mice were used in this study, including wild-type mice and two different transgenic mouse strains. Different groups of these mice were fed high-fat or low-fat diets or liquid diets with and without the addition of alcohol. Proton spectra were collected at baseline and, subsequently, every 4 weeks for up to 16 weeks. Immediately after the last MRS measurement, mice were killed and their livers analyzed for triglyceride level by conventional wet-chemistry methods. The excellent correlation between in vivo MRS and ex vivo wet-chemistry determinations of liver lipids validates the MRS method. These results clearly demonstrate that in vivo MRS will be an extremely valuable technique for longitudinal studies aimed at providing important insights into the genetic, environmental, and dietary factors affecting fat deposition and accumulation within the mouse liver.
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Affiliation(s)
- J R Garbow
- Department of Chemistry and Alvin J Siteman Cancer Center, Washington University, St. Louis, MO 63130, USA.
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Abstract
Advances in the biomedical sciences have been accelerated by the introduction of many new imaging technologies in recent years. With animal models widely used in the basic and pre-clinical sciences, finding ways to conduct animal experiments more accurately and efficiently becomes a key factor in the success and timeliness of research. Non-invasive imaging technologies prove to be extremely valuable tools in performing such studies and have created the recent surge in small animal imaging. This review is focused on three modalities, PET, MR and optical imaging which are available to the scientist for oncological investigations in animals.
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Affiliation(s)
- Jason S Lewis
- Radiation Sciences, Washington University School of Medicine, Saint Louis, MO, USA
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Weitekamp DP, Garbow JR, Murdoch JB, Pines A. High-resolution NMR spectra in inhomogeneous magnetic fields: application of total spin coherence transfer echoes. J Am Chem Soc 2002. [DOI: 10.1021/ja00402a057] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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15
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Lewis JS, Connett JM, Garbow JR, Buettner TL, Fujibayashi Y, Fleshman JW, Welch MJ. 64Cu-PTSM as an inhibitor of tumor recurrence. J Labelled Comp Radiopharm 2001. [DOI: 10.1002/jlcr.2580440130] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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Garbow JR, Likos JJ, Schroeder SA. Structure, dynamics, and stability of beta-cyclodextrin inclusion complexes of aspartame and neotame. J Agric Food Chem 2001; 49:2053-2060. [PMID: 11308366 DOI: 10.1021/jf001122d] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Studies of the high-intensity sweetener aspartame show that its stability is significantly enhanced in the presence of beta-cyclodextrin (beta-CyD). At a 5:1 beta-CyD/aspartame molar ratio, the stability of aspartame is 42% greater in 4 mM phosphate buffer (pH 3.1) compared to solutions prepared without beta-CyD. Solution-state (1)H NMR experiments demonstrate the formation of 1:1 beta-CyD/aspartame complexes, stabilized by the interaction of the phenyl-ring protons of aspartame with the H3 and H5 protons of beta-CyD. Inclusion complex formation clearly accounts for the observed stability enhancement of aspartame in solution. The formation of inclusion complexes in solution is also demonstrated for beta-CyD and neotame, a structural derivative of aspartame containing an N-substituted 3,3-dimethylbutyl group. These complexes are stabilized by the interaction of beta-CyD with both phenyl-ring and dimethylbutyl protons. Solid-state NMR experiments provide additional characterization, clearly demonstrating the formation of inclusion complexes in lyophilized solids prepared from solutions of beta-CyD and either aspartame or neotame.
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Affiliation(s)
- J R Garbow
- Analytical Sciences Center, Pharmacia Corporation, 800 North Lindbergh Boulevard, St. Louis, Missouri 63167, USA.
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17
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Abstract
Cutin and suberin are support polymers involved in waterproofing the leaves and fruits of higher plants, regulating the flow of nutrients among various plant organs, and minimizing the deleterious impact of microbial pathogens. Despite the complexity and intractable nature of these plant biopolyesters, their molecular structure and development are amenable to study by suitable solid-state and solution-state NMR techniques. Interactions of tomato cutin with water were examined by solid-state 2H and 13C NMR, showing that water films enhance rapid segmental motions of the acyl chains and are associated with a fivefold increase in surface elasticity upon cutin hydration. The suberization of wounded potato tissues was studied by solid-state 13C NMR, revealing the likely phenylpropanoid structures that permit dense cross-linking of the suberin structure and their proximity to the cell-wall polysaccharides. Finally, two new approaches were developed to elucidate the molecular structures of these biopolymers: partial depolymerization followed by spectroscopic analysis of the soluble oligomers; and swelling of the intact materials followed by magic-angle spinning (MAS) NMR analysis.
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Affiliation(s)
- R E Stark
- Department of Chemistry, College of Staten Island and the Graduate School of the City University of New York, NY 10314, USA.
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18
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Abstract
Magic-angle spinning (MAS) 13C nuclear magnetic resonance (NMR) spectroscopy is a convenient method for nondestructive, quantitative characterization of seed oil composition. We describe results for intact hybrid and transformed canola seeds. The MAS 13C NMR technique complements and agrees with gas chromatography results. The spectral resolution approaches that of neat, liquid oils. MAS 13C NMR data allow quantitative analysis of major oil components, including saturates and oleic, linoleic, and linolenic acyl chains. 13C NMR directly and quantitatively elucidates, triglyceride regiochemistry and acyl chain cis-trans isomers that cannot be quickly detected by other methods. MAS 13C NMR can serve as the primary method for development of near-infrared seed oil calibrations. These NMR methods are nondestructive and attractive for plant-breeding programs or other studies (e.g., functional genomics) where loss of seed viability is inconvenient.
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Affiliation(s)
- W C Hutton
- Nutrition and Consumer Sector, Monsanto, St. Louis, Missouri 63167, USA.
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Arshava B, Breslav M, Antohi O, Stark RE, Garbow JR, Becker JM, Naider F. Long-distance rotational echo double resonance measurements for the determination of secondary structure and conformational heterogeneity in peptides. Solid State Nucl Magn Reson 1999; 14:117-136. [PMID: 10437665 DOI: 10.1016/s0926-2040(99)00018-1] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The utility of rotational echo double resonance (REDOR) NMR spectroscopy for determining the conformations of linear peptides has been examined critically using a series of crystalline and amorphous samples. The focus of the present work was the evaluation of long-distance (> 5 A) interactions using 13C-15N dephasing. Detailed studies of specifically labeled melanostatin and synthetic analogs of the alpha-factor yeast mating hormone show that nitrogen-dephased, carbon-observe REDOR measurements are reliable for distances up to 6.0 A, and that dipolar interactions can be detected for distances up to 7 A. By contrast, nitrogen-observe REDOR gives reliable results only for distances shorter than 5.0 A. To measure distances accurately, REDOR data must be corrected for the effects of natural-abundance spins. These corrections are particularly important for measuring long distances, which are of the greatest value for determining peptide secondary structure. We have developed a spherical shell model for calculating the effect of these background spins. The REDOR studies also indicate that in a lyophilized powder, the tridecapeptide alpha-factor mating pheromone from Saccharomyces cerevisiae (WHWLQLKPGQPMY) probably exists as a distribution of different turn structures around the KPGQ region. This finding revises previous solid-state NMR studies on this peptide, which concluded alpha-factor assumes a distorted type-I beta-turn in the Pro-Gly central region of the molecule [J.R. Garbow, M. Breslav, O. Antohi, F. Naider, Biochemistry, 33 (1994) 10094].
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Affiliation(s)
- B Arshava
- Department of Chemistry, College of Staten Island and the Graduate School of the City University of New York, 10314, USA
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Affiliation(s)
- J. R. Garbow
- Office of Science & Technology, Monsanto Company, 800 North Lindbergh Boulevard, St. Louis, Missouri 63167
| | - D. M. Snyderman
- Office of Science & Technology, Monsanto Company, 800 North Lindbergh Boulevard, St. Louis, Missouri 63167
| | - E. E. Remsen
- Office of Science & Technology, Monsanto Company, 800 North Lindbergh Boulevard, St. Louis, Missouri 63167
| | - D. L. Kurdikar
- Office of Science & Technology, Monsanto Company, 800 North Lindbergh Boulevard, St. Louis, Missouri 63167
| | - A. J. Solodar
- Office of Science & Technology, Monsanto Company, 800 North Lindbergh Boulevard, St. Louis, Missouri 63167
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Abstract
SIMPLTN, a computer program for the simulation of pulse and two-dimensional NMR, is described and illustrated. The program is menu-driven and is designed to run as much like a spectrometer as possible. This approach allows a complete density-matrix calculation to be performed, yet still makes the program easy to use. SIMPLTN serves as a learning tool, and allows the design and testing of new pulse NMR methods. A spin system and a pulse program are defined, and then the program calculates an FID. The simulated data can then be transformed, inspected, and plotted using a variety of commercial NMR software packages. Systems of up to six strongly coupled spins, and almost any common liquid-state pulse program, can be simulated. SIMPLTN includes a batch mode in which simulations may be queued, and parameters may be systematically varied. This paper gives an overview of the program, some of the unique theoretical features of the program, and examples of its use.
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Affiliation(s)
- T Allman
- SoftPulse Software, Guelph, Ontario, N1H 6K9, Canada
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Garbow JR, Breslav M, Antohi O, Naider F. Conformational analysis of the Saccharomyces cerevisiae tridecapeptide mating pheromone by 13C,15N rotational-echo double resonance nuclear magnetic resonance spectroscopy. Biochemistry 1994; 33:10094-9. [PMID: 8060978 DOI: 10.1021/bi00199a037] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The solid-state conformation of [Nle12]alpha-factor, the Saccharomyces cerevisiae tridecapeptide mating pheromone (WHWLQLKPGQPNleY), was investigated by 13C,15N rotational-echo double resonance (REDOR) nuclear magnetic resonance spectroscopy (NMR). Previous high-resolution NMR studies of [Nle12]alpha-factor in solution revealed a transient Type II beta-turn spanning residues 7-10 of the peptide. To investigate this region of [Nle12]alpha-factor in the solid state, a series of four selectively 13C,15N-enriched tridecapeptides were synthesized by solid-phase methods. Carbon-nitrogen distances between the labeled sites in lyophilized samples of [Nle12]alpha-factor were accurately measured by REDOR NMR. Experimentally determined distances were compared with those from calculated models for Type I and Type II beta-turns and for an extended chain. The measured distances indicate that, in a lyophilized powder, the central region of the [Nle12]alpha-factor is not in an extended conformation. The experimental data was most consistent with distances obtained from a distorted Type I beta-turn model.
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Affiliation(s)
- J R Garbow
- Monsanto Corporate Research, Monsanto Company, St. Louis, Missouri 63198
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Garbow JR, Ridley WP, Bork V, Pan Y, Schaefer J. Milacemide metabolism in rat liver and brain slices by solids NMR. Drug Metab Dispos 1994; 22:298-303. [PMID: 8013285] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
The metabolism of 13C- and 15N-labeled milacemide, 2-(pentylamino)-acetamide, has been studied in rat liver and brain slices using solid-state NMR. This analysis is fast and efficient and can be used to monitor both major and minor metabolic pathways in mammalian tissue culture. The NMR work reported herein involves both conventional cross-polarization magic-angle spinning 13C and 15N NMR spectra and rotational-echo double resonance 13C-15N experiments. The latter measure quantitatively the breaking of isotopically labeled carbon-nitrogen chemical bonds. Our results, which are consistent with suggestions from previous metabolic studies, show that the first step in the breakdown of milacemide is the breaking of the pentylamine nitrogen bond to yield pentanoic acid and glycinamide. Total incorporation of 15N label from the resulting glycinamide fragment is comparable in rat liver and brain. In both tissues, considerably more of the 15N label from glycinamide is incorporated than the corresponding 13C label. Differences between the liver and brain tissue are also observed, with more synthesis incorporating the 13C labels taking place in the liver.
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Stark RE, Sohn W, Pacchiano RA, Al-Bashir M, Garbow JR. Following Suberization in Potato Wound Periderm by Histochemical and Solid-State 13C Nuclear Magnetic Resonance Methods. Plant Physiol 1994; 104:527-533. [PMID: 12232102 PMCID: PMC159227 DOI: 10.1104/pp.104.2.527] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
The time course of suberization in wound periderm from potato (Solanum tuberosum L.) has been monitored by histochemical and high-resolution solid-state nuclear magnetic resonance (NMR) methods. Light microscopy conducted after selective staining of the lipid and double-bonded constituents shows that suberin is deposited at the outermost intact cell-wall surface during the first 7 d of wound healing; suberization forms a barrier to tissue infiltration at later times. Cross polarization-magic angle spinning 13C NMR spectra demonstrate the deposition of a polyester containing all major suberin functional groups after just 4 d of wound healing. Initially the suberin includes a large proportion of aromatic groups and fairly short aliphatic chains, but the spectral data demonstrate the growing dominance of long-chain species during the period 7 to 14 d after wounding. The results of preliminary 13C-labeling experiments with sodium [2-13C]acetate and DL-[1-13C]phenylalanine provide an excellent prospectus for future NMR-based studies of suberin biosynthesis.
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Affiliation(s)
- R E Stark
- Department of Chemistry, College of Staten Island and the Graduate School of the City University of New York, 2800 Victory Boulevard, Staten Island, New York 10314 (R.E.S., W.S., R.A.P., M.A.-B)
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Abstract
Cross-polarization magic-angle spinning (CPMAS) 13C NMR spectroscopy has been used to characterize covalent conjugates of alachlor, an alpha-chloroacetamide hapten, with glutathione (GSH) and bovine serum albumin (BSA). The solid-state NMR method demonstrates definitively the covalent nature of these conjugates and can also be used to characterize the sites of hapten attachment to proteins. Three different sites of alachlor binding are observed in the BSA system. Accurate quantitation of the amount of hapten covalently bound to GSH and BSA is reported. The solid-state 13C NMR technique can easily be generalized to study other small molecule/protein conjugates and can be used to assist the development and refinement of synthetic methods needed for the successful formation of such protein alkylation products.
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Affiliation(s)
- J R Garbow
- Monsanto Company, Life Sciences Research Center, St. Louis, Missouri 63198
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Abstract
Samples of hard wheat flour and dough are analyzed by magic-angle spinning 13C NMR spectroscopy. Cross-polarization magic-angle spinning (CPMAS) 13C NMR spectra of the dry flour allow its starch and protein content to be accurately measured. These two components are phase-separated. Spectra of hydrated hard wheat doughs are collected under both CPMAS and single-pulse carbon with low-power 1H decoupling conditions. The former report on the macromolecular components of the dough, while the latter reveal small molecules which are solubilized by the water. Results of the present study are interpreted as indicating that the protein is largely unaffected by the added water and remains phased-separated from the starch, while water causes significant changes in polymer dynamics of the starch component.
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Affiliation(s)
- J R Garbow
- Physical Sciences Center, Monsanto Corporate Research, Monsanto Company, St. Louis, MO 63198
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Abstract
High-resolution, solid-state (13)C nuclear magnetic resonance (NMR) spectra are reported for suberized cell wall from potatoes (Solanum tuberosum L.). Through experiments combining the techniques of cross polarization and magic-angle spinning, we verified that suberin, like cutin, is a polyester and demonstrated that it also has phenylpropanoid groups characteristic of lignin. Roughly 50% of the suberized material consists of cell-wall polymers; aromatics and other unsaturated linkages outnumber methylene groups 2:1. In conjunction with traditional direct-polarization NMR results, these experiments provide support for prior suggestions that suberin and cell-wall components are chemically bonded via aromatic groups.
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Affiliation(s)
- J R Garbow
- Life Sciences NMR Center, Monsanto Company, St. Louis, Missouri 63198
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Abstract
The partial collapse of dipolar and chemical shift tensors for peptide NH and for the amide NH at cross-link sites in cell wall peptidoglycan, of intact lyophilized cells of Aerococcus viridans, indicates NH vector root-mean-square fluctuations of 23 degrees. This result is consistent with the local mobility calculated in typical picosecond regime computer simulations of protein dynamics in the solid state. The experimental root-mean-square angular fluctuations for both types of NH vectors increase to 37 degrees for viable wet cells at 10 degrees C. The similarity in mobilities for both general protein and cell wall peptidoglycan suggests that one additional motion in wet cells involves cooperative fluctuations of segments of cell walls, attached proteins, and associated cytoplasmic proteins.
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Affiliation(s)
- J R Garbow
- Monsanto Company, Life Sciences NMR Center, Chesterfield, Missouri 63198
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Abstract
Metabolism of glyphosate (N-phosphonomethylglycine) by Pseudomonas sp. strain LBr, a bacterium isolated from a glyphosate process waste stream, was examined by a combination of solid-state 13C nuclear magnetic resonance experiments and analysis of the phosphonate composition of the growth medium. Pseudomonas sp. strain LBr was capable of eliminating 20 mM glyphosate from the growth medium, an amount approximately 20-fold greater than that reported for any other microorganism to date. The bacterium degraded high levels of glyphosate, primarily by converting it to aminomethylphosphonate, followed by release into the growth medium. Only a small amount of aminomethylphosphonate (about 0.5 to 0.7 mM), which is needed to supply phosphorus for growth, could be metabolized by the microorganism. Solid-state 13C nuclear magnetic resonance analysis of strain LBr grown on 1 mM [2-13C,15N]glyphosate showed that about 5% of the glyphosate was degraded by a separate pathway involving breakdown of glyphosate to glycine, a pathway first observed in Pseudomonas sp. strain PG2982. Thus, Pseudomonas sp. strain LBr appears to possess two distinct routes for glyphosate detoxification.
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Affiliation(s)
- G S Jacob
- Physical Sciences Centre, Monsanto Co., St. Louis, Missouri 63167
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Schaefer J, Kramer KJ, Garbow JR, Jacob GS, Stejskal EO, Hopkins TL, Speirs RD. Aromatic cross-links in insect cuticle: detection by solid-state 13C and 15N NMR. Science 1987; 235:1200-4. [PMID: 3823880 DOI: 10.1126/science.3823880] [Citation(s) in RCA: 192] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Cross-polarization magic-angle-spinning nuclear magnetic resonance spectroscopy has been used to determine insect cuticle composition and cross-link structure during sclerotization or tanning. Unsclerotized cuticle from newly ecdysed pupae of the tobacco hornworm, Manduca sexta L., had a high protein content with lesser amounts of lipid and chitin. Concentrations of chitin, protein, and catechol increased substantially as dehydration and sclerotization progressed. Analysis of intact cuticle specifically labeled with carbon-13 and nitrogen-15 revealed direct covalent linkages between ring nitrogens of protein histidyl residues and ring carbons derived from the catecholamine dopamine. This carbon-nitrogen adduct was present in chitin isolated from cuticle by alkaline extraction and is probably bound covalently to chitin. These data support the hypothesis that the stiffening of insect cuticle during sclerotization results primarily from the deposition of protein and chitin polymers and their crosslinking by quinonoid derivatives of catecholamines.
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Coker GT, Garbow JR, Schaefer J. N and C NMR determination of methionine metabolism in developing soybean cotyledons. Plant Physiol 1987; 83:698-702. [PMID: 16665310 PMCID: PMC1056428 DOI: 10.1104/pp.83.3.698] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
The metabolism of d- and l-methionine by immature cotyledons of soybean (Glycine max, L. cv Elf) grown in culture has been investigated using solid-state (13)C and (15)N nuclear magnetic resonance. d-Methionine is taken up by the cotyledons and converted to an amide, most likely by N-malonylation. About 16% of the l-methionine taken up is incorporated intact into protein, and 25% remains as soluble methionine. Almost two-thirds of the l-methionine that enters the cotyledons is degraded. The largest percentage of this is used in transmethylation of the carboxyl groups of pectin. Methionine is not extensively converted to polyamines. We attribute the stimulation of growth of the cotyledons by exogenous methionine to the bypassing of a rate-limiting methyl-transfer step in the synthesis of methionine itself, and subsequently of pectins and proteins.
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Affiliation(s)
- G T Coker
- Department of Biology, Washington University, St. Louis, Missouri 63130
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Jacob GS, Garbow JR, Schaefer J, Kishore GM. Solid-state NMR studies of regulation of N-(phosphonomethyl)glycine and glycine metabolism in Pseudomonas sp. strain PG2982. J Biol Chem 1987; 262:1552-7. [PMID: 3100535] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Lyophilized samples of Pseudomonas sp. PG2982 grown on 13C- and 15N-labeled glyphosate have been analyzed by single and double cross-polarization 13C NMR. Both the carbon and nitrogen metabolism of glyphosate are significantly influenced by the nitrogen source used for the growth of the organism. When ammonium sulfate is the source of nitrogen, the glycyl moiety of glyphosate is utilized intact for the biosynthesis of purines and proteins. But when the organism is grown on glycine as the source of nitrogen, the carbons and nitrogen of glyphosate are scrambled, consistent with incorporation into serine and pyruvate, and hence participation in general metabolism. When both ammonium and glycine are present in the growth medium, regulation of the metabolic fluxes along each of the two major pathways appears to be determined by the intracellular glycine concentration.
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Jacob GS, Schaefer J, Garbow JR, Stejskal EO. Solid-state NMR studies of Klebsiella pneumoniae grown under nitrogen-fixing conditions. J Biol Chem 1987; 262:254-9. [PMID: 2432059] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
The carbon and nitrogen metabolism of Klebsiella pneumoniae M5a1 has been characterized using 13C and 15N labeling with detection by cross-polarization magic-angle spinning solid-state NMR. Cells grown on ammonium typically require some 20 h to derepress fully for nitrogenase when transferred to medium devoid of any source of fixed nitrogen. We have established that during this period some cellular proteins are catabolized with the liberated nitrogen being used for the synthesis of purines needed for formation of ribosomal RNA. The 20-h derepression period can be shortened to 6 h by the introduction of fixed nitrogen in certain specific forms. Serine is the most successful agent we have examined for shortening the derepression period and glycine among the least successful. We attribute this difference to the advantage of serine over glycine in providing both specific and nonspecific carbon and nitrogen sources for complete purine synthesis. These determinations were made by tracing the metabolism of 13C- and 15N-labeled chemical bonds from the 2 amino acids during derepression.
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Jacob GS, Schaefer J, Garbow JR, Stejskal EO. Solid-state NMR studies of Klebsiella pneumoniae grown under nitrogen-fixing conditions. J Biol Chem 1987. [DOI: 10.1016/s0021-9258(19)75919-5] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
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Jacob GS, Garbow JR, Schaefer J. Direct measurement of poly(beta-hydroxybutyrate) in a pseudomonad by solid-state 13C NMR. J Biol Chem 1986; 261:16785-7. [PMID: 3782143] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Four narrow lines are observed in the high-resolution cross-polarization magic-angle spinning 13C NMR spectra of intact, lyophilized samples of Pseudomonas sp. LBr, in addition to the broader lines normally associated with bacterial cellular material. These narrow lines arise from poly(beta-hydroxybutyrate). The cellular carbon contained in this storage material can be measured quantitatively and nondestructively from the solid-state NMR spectra. We find that cells starved for phosphorus store up to 50% of their total carbon as poly(beta-hydroxybutyrate). When such cells are used to inoculate medium containing a source of phosphorus, all of the poly(beta-hydroxybutyrate) is metabolized by the time the culture has reached midlogarithmic growth phase.
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Schaefer J, Garbow JR, Jacob GS, Forrest TM, Wilson GE. Characterization of peptidoglycan stem lengths by solid-state 13C and 15N NMR. Biochem Biophys Res Commun 1986; 137:736-41. [PMID: 3729935 DOI: 10.1016/0006-291x(86)91140-x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Lyophilized whole cells of Aerococcus viridans (Gaffkya homari) grown on a synthetic medium containing D-[2-13C, 15N]Ala, or containing both L-[1-13C]Lys and D-[15N]Ala, have been examined by double cross-polarization magic-angle spinning 13C and 15N nuclear magnetic resonance. Results from the double-labeled alanine experiment confirm the absence of metabolic scrambling of alanine by A. viridans. Results from the combined single-label experiment can be used to count directly the number of adjacent L-Lys and D-Ala units in peptide chains of cell-wall peptidoglycan. This count leads to the conclusion that there are no terminal D-Ala or D-Ala-D-Ala units in uncross-linked chains of the peptidoglycan of A. viridans.
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Weitekamp DP, Garbow JR, Pines A. Erratum: Determination of dipole coupling constants using heteronuclear multiple quantum NMR [J. Chem. Phys. 77, 2870 (1982)]. J Chem Phys 1984. [DOI: 10.1063/1.447299] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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