Effect of the human plasma apolipoproteins and phosphatidylcholine acyl donor on the activity of lecithin: cholesterol acyltransferase.
The human plasma apoproteins apoA-I and apoC-I enhanced the activity of partially purified lecithin: cholesterol acyltransferase five to tenfold with chemically defined phosphatidylcholine:cholesterol single bilayer vesicles as substrates. By contrast, apoproteins apoA-II, apoC-II, and apoC-III did not give any enhancement of enzyme activity. The activation by apoA-I and apoC-I differed, depending upon the nature of the hydrocarbon chains of phosphatidylcholine acyl donor. ApoA-I was most effective with a phosphatidylcholine containing an unsaturated fatty acyl chain. ApoC-I activated LCAT to the same extent with both saturated and unsaturated phosphatidylcholine substrates. Two of the four peptides obtained by cyanogen bromide cleavage of apoA-I retained some ability to activate LCAT. The efficacy of each of these peptides was approximately 25% that of the whole protein. Cyanogen bromide fragments of apoC-I were inactive. The apoproteins from HDL, HDL2, and HDL3, at low protein concentrations, were equally effective as activators of LCATand less effective than apoA-I. Higher concentrations of apoHDL, apoHDL2, and apoHDL3 inhibited LCAT activity. ApoC and apoA-II were both found to inhibit the activation of LCAT by apoA-I. The inhibition of LCAT by higher concentrations of apoHDL was not correlated with the aopA-II and apoC content.
D000217:Acyltransferases / Q000097:blood*; D001059:Apoproteins / Q000097:blood / Q000502:physiology*; D002850:Chromatography, Gel; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D007700:Kinetics; D008075:Lipoproteins, HDL / Q000097:blood / Q000502:physiology*; D009994:Osmolar Concentration; D007862:Phosphatidylcholine-Sterol O-Acyltransferase / Q000097:blood*; D012965:Sodium Chloride / Q000494:pharmacology; D014508:Urea
D001059:Apoproteins; D008075:Lipoproteins, HDL; D012965:Sodium Chloride; D014508:Urea; D000217:Acyltransferases; D007862:Phosphatidylcholine-Sterol O-Acyltransferase