Molecular species of phosphatidylcholine in familial lecithin-cholesterol acyltransferase deficiency: effect of enzyme supplementation.

We studied the molecular species composition of plasma phosphatidylcholine (PC) in three patients with familial deficiency of lecithin-cholesterol acyltransferase in order to determine whether certain species are increased in the absence of this enzyme activity. Compared to normal plasma, the deficient plasma contained significantly higher percentages of 16:0-18:2 and 18:0-18:2 species and lower percentages of 16:0-20:4 and 18:0-20:4 species. The bulk of the total plasma PC as well as the abnormal composition of molecular species were found in the very-low-density and low-density lipoprotein (VLDL + LDL) fractions. When the deficient plasma was incubated with partially purified enzyme from normal human plasma, there was a significant reduction in the amounts of most major species, mainly in the VLDL + LDL fraction. When the selectivity factors were calculated by dividing the percentage contribution of each species for cholesterol esterification by its percentage concentration, the highest selectivity factors were found for 16:0-18:2, 18:1-18:1 and 18:1-18:2. The order of selectivity of the enzyme for various species was very similar to that obtained earlier using normal HDL as substrate. These results show that lecithin-cholesterol acyltransferase has significant effects on the molecular species composition of plasma PC and the deficiency of the enzyme results in accumulation of certain PC species normally used by the enzyme, as well as in abnormal distribution of these species among the lipoproteins.