Inhibition of the binding of cytochrome b5 to phosphatidylcholine vesicles by cholesterol.

The binding of cytochrome b5 to single-walled liposomes of egg phosphatidylcholine was inhibited by the presence of cholesterol in the lipid bilayer under conditions where a limited amount of liposomes was incubated with the cytochrome. Since similar conditions seem to apply for the binding of cytochrome b5 to erythrocyte ghosts, this observation supports the conclusion of Enomoto and Sato (Enomoto, K. and Sato, R. (1977) Biochim. Biophys. Acta 466, 136--147) that the localization of cholesterol on the outer surface of the ghost membrane prevents the binding of cytochrome b5 to this surface. The finding reported by Roseman et al. (Roseann, M.A., Holloway, P.W. and Calabro, M.A. (1978) Biochmi. Biophys. Acta 507, 552--556) that cholesterol did not prevent the cytochrome binding to phosphatidylcholine liposomes in the presence of a large excess of liposomes could be confirmed in the present study, but this does not contradict the abovementioned conclusion.