Inhibition of lecithin cholesterol acyltransferase by phosphatidylcholine hydroperoxides

To gain insight into the nature of the lecithin-cholesterol acyltransferase inhibitory factor(s), we separated and collected the oxidation products from oxidized lipoproteins after lipoxygenase treatment. Isolated fractions identified by chemiluminescence, as hydroperoxides of phosphatidylcholine, were found to produce a significant reduction of lecithin-cholesterol acyltransferase activity, The reaction kinetics of lecithin-cholesterol acyltransferase with reconstitued high density lipoproteins were studied in the presence of 0.6 and 1.2 mu M hydroperoxides of phosphatidlylcholine. No significant changes in the apparent V-max were observed but a concentration-dependent increase in slope of the reciprocal plots and in the apparent K-m values mas observed with increasing hydroperoxide concentrations. These results show that the active site of lecithin-cholesterol acyltransferase is not affected by the presence of phosphatidylcholine hydroperoxides. Nevertheless, hydroperoxides of phosphatidylcholine altered the reactivity of lecithin-cholesterol acyltransferase for reconstitued high density Lipoproteins suggesting either an alteration of the binding of lecithin-cholesterol acyltransferase to the reconstitued high density lipoproteins or a competitive inhibition mechanism. (C) 1999 Federation of European Biochemical Societies.