EFFECT OF 2 OH-SUBSTITUTED CHOLESTEROL DERIVATIVES ON MONOLAYER CONDENSATION AND MEMBRANE CLOSURE

The faculty of cholesterol to condense monolayers of phosphatidylcholine is not shared by the OH-blocked, amphiphilic derivatives O-(methoxyethoxyethoxyethyl)-cholesterol (I) and cholesterylphosphorylcholine (II). Compound I also does not affect the permeability of phosphatidylcholine or dihydrosphingomyelin bilayers (liposomes) against glycerol, nor the entropy of activation of permeability. Compound II, however, reduces premeability as effectively as cholesterol. Contrary to cholesterol, it does not reduce the entropy of activation of permeation when added to dihydrosphingomyelin bilayers. These results are in harmony with the concept of a lipid-lipid hydrogen bond donor-acceptor balance in biological membranes. They also show that monolayer condensation and membrane closure are not necessarily parallel phenomena, and that a free β-OH group of the sterol is not a necessary condition for membrane closure. © 1979.