Electron paramagnetic resonance studies of membrane proteins in hepatic microsomes |
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Authors: | Michael J Barber Andrew S Zektzer Gerald M Rosen Helen A Demos Elmer J Rauckman |
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Institution: | 1. Department of Biochemistry, University of South Florida College of Medicine, Tampa, FL 33612 U.S.A.;2. Department of Pharmacology, Duke University Medical Center, Durham, NC 27710 U.S.A.;3. Department of Surgery, Duke University Medical Center, Durham, NC 27710 U.S.A. |
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Abstract: | Hepatic microsomal membranes, prepared under various conditions that yield either ‘intact’ or ‘disrupted’ microsomal vesicles, have been labeled via the sulfhydryl groups of intrinsic membrane proteins using nitroxide analogs of . Electron paramagnetic resonance spectra revealed the presence of two dominant classes of bound label corresponding to differing degrees of immobilization, the ratio of which were quantitated using a parameter designated the ‘’ ratio. For latent microsomes, the value of this parameter was determined to be and was influenced by factors such as label/protein ratio, incubation period, nitroxide structure, temperature and pH. The ratio was also sensitive to the degree of membrane integrity as revealed by the latency of mannose 6-phosphate activity of glucose-6-phosphohydrolase. In addition, membrane disruption resulted in a corresponding decrease in the order parameter for nitroxide-labeled fatty acids intercalated within the lipid bilayer. The ratio was observed to be dependent upon the method of microsome preparation yielding values of for ‘hypertonically disrupted’ vesicles and for ‘mechanically disrupted’ vesicles. Microsomal marker enzymes such as cytochrome and FAD-containing monooxygenase retained significant levels of functionally following nitroxide incorporation. |
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Keywords: | ESR Spin-label Microsomal membrane Membrane protein (Rat liver) Bicine CAPS cyclohexylaminopropanesulfonic acid CHES Hepes Mes Mal-6 4-maleimide-2 2 6 6-tetramethylpiperidinooxyl |
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