title: Spin-label saturation-recovery EPR at W-band: applications to eye lens lipid membranes.
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.
authors: Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI 53226, USA.
authors: Laxman
authors: L
authors: Mainali
authors: Marija
authors: M
authors: Raguz
authors: Theodore G
authors: TG
authors: Camenisch
authors: James S
authors: JS
authors: Hyde
authors: Witold K
authors: WK
authors: Subczynski
mesh_terms: D000818:Animals; D001693:Biological Transport, Active; D002462:Cell Membrane / Q000737:chemistry; D002784:Cholesterol; D003627:Data Interpretation, Statistical; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D007202:Indicators and Reagents; D007908:Lens, Crystalline / Q000737:chemistry*; D008051:Lipid Bilayers / Q000737:chemistry; D008560:Membrane Fluidity; D008563:Membrane Lipids / Q000737:chemistry*; D008566:Membranes / Q000737:chemistry*; D010101:Oxygen Consumption / Q000502:physiology; D010713:Phosphatidylcholines / Q000737:chemistry; D013113:Spin Labels; D013229:Stearic Acids / Q000737:chemistry; D013552:Swine
chemical_list: D007202:Indicators and Reagents; D008051:Lipid Bilayers; D008563:Membrane Lipids; D010713:Phosphatidylcholines; D013113:Spin Labels; D013229:Stearic Acids; D002784:Cholesterol