The Behavior of Two Oxidized Derivatives of Cholesterol in Model Membranes

Abstract

bilayer and therefore plays an important role in maintaining lipid asymmetry. Leaflet composition is regulated by the active transport of lipids by membrane proteins, while thermal diffusion across a membrane tries to randomize the leaflet composition. We have measured the transbilayer diffusion rates for three different sterols over a wide range of compositions. The sterols studied were all cholesterol analogs; including dihydrocholesterol, ergosterol, a component of fungal cell membranes, and stigmasterol, an unsaturated plant sterol. Temperature was varied to determine its influence on transbilayer diffusion rates. We find that sterol structure does have an influence on the rate at which lipids move between bilayer leaflets. Transbilayer diffusion measurements were made using a sodium dithionite assay to monitor the location of lipid analogues within DMPC/sterol liposomes.