Differential effects of cholesterol and lanosterol on artificial membranes.

Abstract
The effects of cholesterol, 4,4-dimethylcholesterol, and lanosterol (4,4'',14.alpha.-trimethyl-.DELTA.824-cholestadiene-3.beta.-ol) on some properties of lecithin vesicles were compared. Unlike cholesterol, lanosterol retards the exit of trapped glucose from phospholipid vesicles only slightly. The 13C NMR spectrum of cholesterol/lecithin vesicles shows no resonances attributable to the sterol. Several resonances attributable to quaternary C atoms or methyl groups are seen in the 13C NMR spectrum of lanosterol/lecithin vesicles, indicating that lanosterol is much less immobilized than cholesterol. Because the membrane behavior of 4,4-dimethylcholesterol is closely similar to that of cholesterol, the axial 14-.alpha.-methyl group is probably responsible for the lessened membrane immobilization of lanosterol. The results emphasize the importance of a planar sterol .alpha.-face for interaction with phospholipid acyl chains.