Studies on the Isolation and Characterization of an Inhibitor of Human Plasma Lipid Transfer Activities
McVittie, Loris D.
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Protein(s) which inhibit the transfer of both triacy1g1ycero1 and cho1estery1 ester from very low (VLDL) and low (LOL) density lipoproteins to high density (HOL) lipoproteins but not from HOL to VLDL or LOL have been isolated from lipoprotein-free human plasma by ultracentrifugation at d = 1.21 glm1 and gel filtration chromatography. The protein-lipid complex purified by gel filtration chromatography on Bio-Ge1 A5m (molecular weight shown to be ~5,OOO,OOO) is sensitive to heating and trypsin treatment, and requires a lipid complement to maintain its inhibitory activity. Based upon electrophoretic and immunological behavior, the protein appears to be a form of apolipoprotein B. It is suggested that the inhibitor shows a preferential interaction with the lipid transfer complex and thus prevents the protein-facilitated transfer of triacylg1ycero1 and cho1esteryl ester from VLDL or LDL to HOL. The inhibitor does not appear to affect the interaction of HOL with the lipid transfer complex.