title: Activation of lecithin: cholesterol acyltransferase by apolipoproteins E-2, E-3, and A-IV isolated from human plasma.
abstract: Apolipoprotein A-IV, apolipoprotein E-2 and apolipoprotein E-3 were individually incorporated into defined phosphatidylcholine/cholesterol liposomes for study of lecithin:cholesterol acyltransferase activation. Enzyme activities obtained with these liposomes were compared with that from liposomes containing purified apolipoprotein A-I. Apolipoprotein A-IV, apolipoprotein E-2, and apolipoprotein E-3 all activated lecithin:cholesterol acyltransferase. With purified enzyme and with egg yolk phosphatidylcholine as the acyl donor, maximal activation was obtained at a concentration of approximately 0.5 nmol for apolipoprotein A-IV and 0.4 nmol for the apolipoprotein E isoforms. Apolipoprotein A-IV was approximately 25% as efficient as apolipoprotein A-I for the activation of purified enzyme; apolipoprotein E-2 was 40% as efficient, and apolipoprotein E-3, 30%. Similar activation results were obtained using plasma as the enzyme source. Analysis of the plasma of patients with absence of apolipoprotein A-I or with only trace amounts of apolipoprotein A-I exhibited a reduced rate of cholesterol esterification and lecithin:cholesterol acyltransferase activity that was proportional to the reduced level of the enzyme's mass. These results indicate that apolipoprotein A-IV and apolipoprotein E may serve as physiological cofactors for the enzyme reaction.
mesh_terms: D053318:Apolipoprotein E3; D053327:Apolipoprotein E4; D001053:Apolipoproteins / Q000097:blood* / Q000494:pharmacology; D001054:Apolipoproteins A / Q000097:blood; D001057:Apolipoproteins E / Q000097:blood; D004789:Enzyme Activation; D006801:Humans; D007700:Kinetics; D007862:Phosphatidylcholine-Sterol O-Acyltransferase / Q000378:metabolism*; D010713:Phosphatidylcholines
chemical_list: D053318:Apolipoprotein E3; D053327:Apolipoprotein E4; D001053:Apolipoproteins; D001054:Apolipoproteins A; D001057:Apolipoproteins E; D010713:Phosphatidylcholines; C022205:apolipoprotein A-IV; D007862:Phosphatidylcholine-Sterol O-Acyltransferase