title: Stimulation of lecithin:cholesterol acyltransferase activity by apolipoprotein A-II in the presence of apolipoprotein A-I.
abstract: Various combinations of incorporation and addition of apolipoprotein A-I (apo A-I) and apolipoprotein A-II (apo A-II) individually or together to a defined lecithin-cholesterol (250/12.5 molar ratio) liposome prepared by the cholate dialysis procedure were used to study the effect of apo A-II on lecithin:cholesterol acyltransferase (LCAT, EC 2.3.1.43) activity of both purified enzyme preparations and plasma. When apo A-I (0.1-3.0 nmol/assay) alone was incorporated or added to the liposome, apo A-I effectively activated the enzyme. By contrast, when apo A-II (0.1-3.0 nmol/assay) alone was incorporated into or added to the liposome, apo A-II exhibited minimal activation of LCAT activity, approximately 1% of the activity obtained by an equal amount of apo A-I. Addition of apo A-II (0.1-3.0 nmol/assay) together with apo A-I (0.8 nmol/assay) to the liposome reduced the LCAT activity to approximately 30% of the level obtained with addition of apo A-I alone. On the other hand, addition of apo A-II (0.1-3.0 nmol/assay) or addition of lecithin-cholesterol liposome containing apo A-II (0.1-3.0 nmol/assay) to lecithin-cholesterol liposome containing apo A-I (0.8 nmol/assay) did not significantly alter apo A-I activation of LCAT activity. However, when the same amounts (0.1-3.0 nmol/assay) of apo A-II were incorporated together with apo A-I (0.8 nmol/assay) into the liposome, apo A-II significantly stimulated LCAT activity as compared to activity obtained with incorporation of apo A-I alone. The maximal stimulation was obtained with 0.4 nmol apo A-II/assay for both purified and plasma enzyme. At this apo A-II concentration, approximately 4-fold and 1.8-fold stimulation was observed for purified enzyme and plasma enzyme, respectively. These results indicated that apo A-II must be incorporated together with apo A-I into lecithin-cholesterol liposomes to exert its stimulatory effect on LCAT activity and that apo A-II in high-density lipoprotein may play an important role in the regulation of LCAT activity.
authors.forename: C H
authors.initials: CH
authors.lastname: Chen
authors.forename: J J
authors.initials: JJ
authors.lastname: Albers
mesh_terms: D016632:Apolipoprotein A-I; D016633:Apolipoprotein A-II; D001054:Apolipoproteins A / Q000494:pharmacology*; D002784:Cholesterol / Q000378:metabolism; D003956:Dialysis; D004347:Drug Interactions; D004530:Egg Yolk; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D008081:Liposomes / Q000378:metabolism; D007862:Phosphatidylcholine-Sterol O-Acyltransferase / Q000097:blood / Q000378:metabolism*; D010713:Phosphatidylcholines / Q000378:metabolism
chemical_list: D016632:Apolipoprotein A-I; D016633:Apolipoprotein A-II; D001054:Apolipoproteins A; D008081:Liposomes; D010713:Phosphatidylcholines; D002784:Cholesterol; D007862:Phosphatidylcholine-Sterol O-Acyltransferase