Isolation and partial characterization of a glycine-and serine-rich polypeptide from human serum high-density lipoproteins (HDL)

Abstract

Lately, several minor polypeptides characterized by a high content of glycine and serine have been described in human serum lipoproteins. By column chromatography we have isolated a glycine- and serine-rich polypeptide from totally delipidized high-density lipoproteins, apo-HDL. The partial characterization of this polypeptide by total amino acid composition and by immunology utilizing monospecific antisera to polypeptides of human serum lipoproteins, would indicate a unique polypeptide. This low molecular weight (4900 Daltons) glycine- and serine-rich polypeptide was characterized by a mobility on poly-acrylamide gel electrophoresis, similar to that of polypeptide A-I, a blocked NH₂-terminal amino acid and a terminal COOH-fragment consisting of R-Ser-Ala-Gly-Gly. There are similarities between this polypeptide and the protein moiety of a cholesterol ester-rich lipoprotein fraction, HDL^sup, obtained by in vitro incubation of HDL subtractions and described in earlier publications by our group. The identity between these two polypeptides, however, cannot be confirmed by the present study.

Key Words:

• glycine
• lipoprotein
• high density
• polypeptide
• serine