[Role of phosphorylcholine group on inhibiting capacity of lecithin-cholesterol liposomes on streptolysin O].

Cholesterol inhibition of the hemolytic activity of streptolysin O was used for testing the presence of cholesterol on the surface of lecithin-cholesterol liposomes. Cholesterol as a liposome component is not available for streptolysin inhibition when the molar ratio lecithin-cholesterol greater than 1,25. Incubation of such liposomes with phospholipase C, which converts the phosphadylcholine group into neutral diglycerides, restores an inhibiting activity of cholesterol parallel to the phosphatid degradation. Incubation of the liposomes with phospholipase D, which converts the phosphatidylcholine group into phosphatidic acid, also restores the inhibiting capacity of cholesterol on the hemolysin. The accessibility of liposome cholesterol to streptolysin O appears to mainly depend upon the cholin group of lecithin.