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 microM hydroperoxides of phosphatidylcholine. No significant changes in the apparent Vmax were observed but a concentration-dependent increase in slope of the reciprocal plots and in the apparent Km values was 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.
Davit-Spraul
A
A
Biochimie, Hôpital Bicêtre, Laboratoire de Biochimie, Le Kremlin Bicêtre, France. cct@kb.inserm.fr
Thérond
P
P
Leroy
A
A
Palmade-Rieunier
F
F
Rousset
C
C
Moatti
N
N
Legrand
A
A
D016632:Apolipoprotein A-I; D002784:Cholesterol; D002851:Chromatography, High Pressure Liquid; D004305:Dose-Response Relationship, Drug; D015227:Lipid Peroxidation; D008075:Lipoproteins, HDL; D007862:Phosphatidylcholine-Sterol O-Acyltransferase / Q000037:antagonists & inhibitors*; D010713:Phosphatidylcholines / Q000494:pharmacology*; D010743:Phospholipids
D016632:Apolipoprotein A-I; D008075:Lipoproteins, HDL; D010713:Phosphatidylcholines; D010743:Phospholipids; C057590:phosphatidylcholine hydroperoxide; D002784:Cholesterol; D007862:Phosphatidylcholine-Sterol O-Acyltransferase