Variations in the Condensing Effect of Cholesterol on Saturated versus Unsaturated Phosphatidylcholines at Low and High Sterol Concentration

In this work, we have investigated the condensing and ordering effect induced by cholesterol on phosphatidylcholines (PCs). To perform the studies systematically, for the experiments we have selected phospholipids differing only in the number of cis monounsaturated chains (1,2-distearoyl-sn-glycero-3-phosphocholine − DSPC, 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine − SOPC, 1,2-dioleoyl-sn-glycero-3-phosphocholine − DOPC) or in the length (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine − POPC vs SOPC) of sn-1 acyl chain. Because the cholesterol concentration in mammalian membranes can be as high as 70 mol % of total lipids, the investigations were performed in a wide range of the sterol content. The results of the Langmuir monolayer experiments evidence that the relation between the structure of hydrophobic part of PC and the magnitude of the effects induced by cholesterol found at lower sterol content is different from that observed at higher sterol concentration. At a lower concentration of sterol...