Phospholipid asymmetry and transmembrane diffusion in photoreceptor disc membranes.
The phospholipid asymmetry and flip-flop rate in rod outer segment (ROS) disc membranes has been investigated by both a spin-label reduction method and a novel electron-electron double resonance (ELDOR) method. At 39 degrees C in the absence of ATP, spin-labeled derivatives of phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylserine (PS) undergo rapid transmembrane diffusion, with a half-time of less than 10 min. At equilibrium, approximately 53% of the spin-labeled PC, 37% of the spin-labeled PE, and 18% of the spin-labeled PS reside in the inner (intradiscal) monolayer. The rapid transmembrane diffusion of phospholipids is partially inhibited by N-ethylmaleimide, suggesting that the process is mediated by proteins in the disc membrane.
Jules Stein Eye Institute, University of California, Los Angeles 90024-7008.
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D000818:Animals; D001205:Ascorbic Acid / Q000378:metabolism; D002417:Cattle; D004058:Diffusion / Q000187:drug effects; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D007700:Kinetics; D008566:Membranes / Q000378:metabolism / Q000648:ultrastructure; D008567:Membranes, Artificial; D008954:Models, Biological; D010084:Oxidation-Reduction; D010713:Phosphatidylcholines; D010743:Phospholipids / Q000378:metabolism / Q000494:pharmacology*; D012243:Rhodopsin / Q000031:analogs & derivatives / Q000378:metabolism*; D012374:Rod Cell Outer Segment / Q000378:metabolism* / Q000648:ultrastructure; D013113:Spin Labels
D008567:Membranes, Artificial; D010713:Phosphatidylcholines; D010743:Phospholipids; D013113:Spin Labels; D012243:Rhodopsin; D001205:Ascorbic Acid