The Serum High Density Lipoproteins of Macacus rhesus

Abstract

Abstract The delipidated apoprotein of Macacus rhesus high density lipoprotein of d 1.063 to 1.21 g per ml (HDL) or of its two subclasses, HDL2 (d 1.063 to 1.125 g per ml) or HDL3 (d 1.125 to 1.21 g per ml), was fractionated by a combination of Sephadex G-200 and DEAE-cellulose column chromatography in the presence of urea. Two major polypeptides, operationally termed as Fractions III and IV, were obtained. Fraction III was found to represent a single polypeptide chain with a molecular weight of about 27,000; NH2-terminal, aspartic acid and COOH-terminal, glutamine. This fraction had immunological and spectral properties (circular dichroism) similar to the human product, but differed from it in its content of glutamic acid, methionine, and arginine. Gel isoelectric focusing of this fraction indicated two components (pI values of 5.21 and 5.69) separable by rechromatography on DEAE-cellulose and probably differing in amide content. Fraction IV was a single polypeptide chain of molecular weight of about 8,500 with pyrrolidone carboxylic acid in NH2-terminal position and glutamine as its COOH terminus. The NH2-terminal sequence determined on pyrrolidoxyl peptidase-treated Fraction IV was: pyrrolidone carboxylic acid-Ala-Glu-Glu-Pro-Ser-Val ... . In human IV (or A-II), position 6 is known to be occupied by cysteine which, in turn, is involved in the disulfide linkage of the two identical monomers into dimers. Neither cysteine or cystine was present in Rhesus IV. Thus, the replacement in position 6 of cysteine by serine, observed in Macacus rhesus, appears to account for the natural occurrence of monomers of Fraction IV in this animal species. A minor class of polypeptides, operationally termed Fraction V, was also present in Rhesus apo-HDL. This fraction was probably the one containing carbohydrates since they were present in whole apo-HDL (1.5 g/100 g of protein) but were detected neither in Fraction III nor IV.