The effect of cholesterol (CHOL) on the rate of autoperoxidation of chromatographically pure phosphatidylcholine from hen egg yolks (EYPC) in aerated multilamellar liposomes was examined at eight CHOL:EYPC molar ratios from 0.1 up to 1.0 at 45 °C. Autoperoxidation was measured as conjugated diene (CD) formation by UV-VIS spectrophotometry. In the presence of cholesterol, the initiation and propagation phases of autoperoxidation were prolonged, the autoperoxidation rate in the propagation phase was decreased, and the CD concentration in the termination phase was lowered. The inhibition of EYPC autoperoxidation by cholesterol can originate a) from the increased lateral separation of polyunsaturated EYPC acyl chains caused by intercalation of cholesterol between EYPC molecules, b) from the increased molecular packing of both the bilayer polar and hydrophobic regions due to the reduced bilayer hydration, c) from the decreased concentration of the molecular oxygen in the bilayer interior, and d) from the cholesterol epoxidation and hydroperoxidation induced by the oxidation products of EYPC polyunsaturated acyl chains.

        Key words: peroxidation – liposome – phosphatidylcholine – cholesterol – conjugated dienes