Effect of the human plasma apolipoproteins and phosphatidylcholine acyl donor on the activity of lecithin: cholesterol acyltransferase

Biochemistry. 1975 Jul 15;14(14):3057-64. doi: 10.1021/bi00685a003.


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.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Acyltransferases / blood*
  • Apoproteins / blood
  • Apoproteins / physiology*
  • Chromatography, Gel
  • Enzyme Activation / drug effects
  • Humans
  • Kinetics
  • Lipoproteins, HDL / blood
  • Lipoproteins, HDL / physiology*
  • Osmolar Concentration
  • Phosphatidylcholine-Sterol O-Acyltransferase / blood*
  • Sodium Chloride / pharmacology
  • Urea


  • Apoproteins
  • Lipoproteins, HDL
  • Sodium Chloride
  • Urea
  • Acyltransferases
  • Phosphatidylcholine-Sterol O-Acyltransferase