Cholesterol versus α-Tocopherol: Effects on Properties of Bilayers Made from Heteroacid Phosphatidylcholines

Abstract

The techniques of differential scanning calorimetry, fluorescence of merocyanine 540, fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene, proton permeability, and lipid peroxidation are used to compare the perturbations of cholesterol and α-tocopherol on lipid bilayer membranes composed of different phosphatidylcholines containing stearic acid in the sn-1 position and an unsaturated fatty acid (either oleic, α-linolenic, γ-linolenic, or docosahexaenoic acid) in the sn-2 position. It is concluded that the structural roles of cholesterol and α-tocopherol may be similar with membranes composed of some phosphatidylcholines but are clearly different with membranes composed of other related phosphatidylcholines. α-Tocopherol exerts a much larger effect than cholesterol on membranes rich in polyunsaturated fatty acids that have their initial double bond before the Δ9 position. Cholesterol interacts more favorably with fatty acids that do not have an double bond before the Δ9 position. The membrane structural effects are explained in terms of the larger size of the sterol ring structure of cholesterol compared to the smaller chromanol ring of α-tocopherol.