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 phosphat idylcholines (PC) that is detectable by differential scanning calorime try (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 d etermined. Cholesterol caused a concentration-dependent removal of the detectable phase transitions in all cases. It required very little ch olesterol to remove the phase transition 16:0-18:2 PC (< 17 mol% of ch olesterol in PC). It required greater than or equal to 35 mol% cholest erol 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 magnitu de of the influence of cholesterol on phospholipid is dependent on the degree of unsaturation in the lipid.