Effect of the Human Plasma Apolipoproteins and Phosphatidylcholine Acyl Donor on the Activity of Lecithin: Cholesterol Acyltransferase

Anne K. Soutar, Charles W. Garner, H. Nordean Baker, James T. Sparrow, Richard L. Jackson, Antonio Gotto, Louis C. Smith

Research output: Contribution to journalArticlepeer-review

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Abstract

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 LCAT and 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 apoA-II and apoC content.

Original languageEnglish (US)
Pages (from-to)3057-3064
Number of pages8
JournalBiochemistry
Volume14
Issue number14
DOIs
StatePublished - Jul 1 1975

ASJC Scopus subject areas

  • Biochemistry

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