Heteroacid phosphatidylcholines with different amounts of unsaturation respond differently to cholesterol.

The effectiveness of cholesterol in removing the gel to liquid crystal phase transition of dispersions of pure molecular species of phosphatidylcholines (PC) that is detectable by differential scanning calorimetry (DSC) has been explored. The effect of cholesterol on 16:0-18:0 PC, 16:0-18:1 PC, 16:0-18:2 PC, 16:0-20:4 PC and 16:0-22:6 PC has been determined. Cholesterol caused a concentration-dependent removal of the detectable phase transitions in all cases. It required very little cholesterol to remove the phase transition 16:0-18:2 PC (< 17 mol% of cholesterol in PC). It required > or = 35 mol% cholesterol to remove delta H for 16:0-18:0 PC and 16:0-22:6 PC. About 20-25 mol% cholesterol caused disappearance of the transitional endotherm of 16:0-18:1 PC and 16:0-20:4 PC. The findings indicate that the magnitude of the influence of cholesterol on phospholipid is dependent on the degree of unsaturation in the lipid.