ISOLATION AND CHARACTERIZATION OF POLYPEPTIDES OF HUMAN SERUM LIPOPROTEINS

Two or more different polypeptides were isolated by DEAE-cellulose chromatography from each of the protein moieties of several fractions of human serum lipoproteins. The polypeptides were characterized by amino acid composition, carboxyl-terminal analysis, and polyacrylamide gel electrophoresis. The high-density lipoproteins of density 1.083-1.124 g/cc (HDL2) were more heterogeneous than those of density 1.126-1.195 g/cc (HDL3) with respect to polypeptide content and contained several polypeptides in addition to the two which comprise most of the protein of the HDL3 fraction. The low-density lipoprotein fraction of density 0.98-1.006 g/cc (Sf 20-100) also contains several polypeptides, two of which are similar to if not identical with peptides found as minor components in the high-density lipoproteins. The protein of the low-density lipoprotein fraction of density 1.029-1.039 g/cc (Sf 4-8 lipoproteins) yielded two polypeptides, which were different from the peptides of high-density lipoproteins and the Sf 20-100 fraction of low-density lipoproteins. Multiple forms, differing slightly in amino acid composition, of some of the peptides were found. The highdensity lipoproteins and the low-density lipoproteins may be structurally and metabolically related by their content of lipid complexes of two polypeptides, one of which has carboxyl-terminal R-Ala-Val-Ala-Ala and one of which has an unusually high content of glycine, serine, and glutamic acid, which are major components of Sf 20-100 lipoproteins and minor components of HDL2 lipoproteins. © 1969, American Chemical Society. All rights reserved.