Steroid-phosphatidylcholine interactions in oriented multbilayers—A spin label study

Abstract

1. 1. The effects of incorporated cholesterol, and structural derivatives, upon the molecular motion of egg phosphatidylcholine in oriented multibilayers has been investigated using spin labelled lipid probes. 2. 2. Addition of cholesterol to the multibilayers decreases the amplitude of motion of the lipid probes, indicating an increase in order of the phospholipids. 3. 3. Cholesterol, lathosterol and 7-dehydrocholesterol are as effective as cholesterol in reducing the random motion of the bilayer phospholipids. 4. 4. Cholesteryl methyl ether, cholesteryl chloride, 4-cholesten-3-one, thiocholesterol and epicholesterol have no significant ordering effect. 5. 5. The plant sterols ergosterol and β-sitosterol have little ordering effect while sterols lacking the C-17 side , 5α-androstane-3β-ol and 5α-androstane-3β-ol-17-one, produce no detectable effect. 6. 6. For maximum interaction with phosphatidylcholine a steroid with a planar nucleus requires a C-3 β-hydroxyl group and an iso-octyl group at C-17, indicating the importance of stereospecific polar and hydrophobic forces in steroid-phospholipid interactions.