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Abstract
Abstract High density lipoproteins (HDL) were isolated from pig plasma by ultracentrifugal flotation between densities 1.063 and 1.210 g per ml. After delipidation, the apolipoproteins were fractionated by chromatography on Sephadex G-150 and DEAE-cellulose in 5.4 m urea. One major apolipoprotein was isolated and characterized. From its chemical and physical properties, this major apolipoprotein appears very similar to apoLP-Gln-I from human HDL. Pig HDL appears to differ from human HDL in a marked decrease in the relative content of apoLP-Gln-II in the pig lipoprotein family. A distinct peak associated with apoLP-Gln-II was not identified by chromatography of pig apoHDL. A small quantity of a protein with the same mobility of human apoLPGln-II was detected in pig apoHDL after polyacrylamide gel electrophoresis in sodium dodecyl sulfate. The major apolipoprotein from pig HDL had an approximate molecular weight of 26,000 as determined by polyacrylamide gel electrophoresis in sodium dodecyl sulfate. Its calculated molecular weight from amino acid analysis was 29,800. Rabbit antisera prepared against the pig apolipoprotein formed precipitin lines of partial identity between this protein and apoLP-Gln-I from human HDL. Treatment of the pig apolipoprotein with carboxypeptidase established Leu-Gln as the COOH-terminal sequence. Pig and human apoLPGln-I had similar amino acid compositions, but the pig protein contained isoleucine and had 12 more residues of alanine than did human apoLP-Gln-I. Pig and human apoLP-Gln-I had indistinguishable absorption spectra and similar circular dichroism spectra indicating a relatively high content of α-helical conformation. Both proteins activated human lecithin : cholesterol acyltransferase. These studies demonstrate that the major apolipoprotein from human and pig HDL have similar chemical, immunological, physical, and physiological properties.
Highlights
From its chemical and physical properties, this major apolipoprotein appears very similar to apoLP-Gln-I from human High density lipoproteins (HDL)
Tryptophan was determined by the method of Liu and General Methods-Polyacrylamide gel electrophoresis in sodium dodecyl sulfate was performed as described by Weber and Osborn
The major apolipoprotein isolated over these two ranges of salt concentrations were indistinguishable by all criteria tested, including amino acid analysis, polyacrylamide gel electrophoresis, and immunological reactions
Summary
While the apolipoproteins of HDL’ serve as transport units for neutral lipids and phoxpholipids in the blood, it has recently been shown that apoLP-Gln-I may be required for activation of the enzyme, lecithin:cholesterol acyltransferase [12] This enzyme catalyzes the transfer of a fatty acyl moiety from phospholipid to unrsterified cholesterol. &cause of the use of the pig model to study arteriosclerosis and the presumed relationship between plasma lipids and lipoproteins and the pathogenesis of arteriosclerosis, we have undertaken a detailed investigation of the apolipoprotcin components of pig lipoproteins It is the purpose of this cornmunication to compare the properties of the major apolipoprotein from swine HDL with its human counterpart, apoLP-Gin-I
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