SOME PHYSICAL AND CHEMICAL STUDIES ON 2 POLYPEPTIDE COMPONENTS OF HIGH-DENSITY LIPOPROTEINS OF HUMAN SERUM

Two different polypeptides separated from the protein moiety of high-density lipoproteins of human serum were found to be similar in molecular weight but very different in amino acid composition. One of the peptides, characterized by carboxyl-terminal glutamine, contains no histidine, arginine, tryptophan, or cysteine. Its amino acid composition is: Lys15,- Cys2,Asp5,Thr11,Ser11, Glu26, Pro7, Gly6, Ala9, Val10, Met2, - Ile2,Leu11,Tyr6,Phe7; the total number of residues is 133 and the molecular weight from amino acid composition is 14,900. Sedimentation equilibrium experiments yielded molecular weight values of 14,300 and 14,900 for the polypeptide R-Gln in urea solutions and in guanidine hydrochloride solutions, respectively. The other polypeptide, characterized by carboxyl- terminal threonine, contains no isoleucine, cystine, or cysteine. Its amino acid composition is: Lys10,His3,Arg9,- Asp13,Thr5, Ser8,Glu24,Pro5, Gly6, Ala10, Val7, Met2,Leu20, - Tyr4,Phe3,Trp4; the total number of residues is 133 and the molecular weight from amino acid composition is 15,500. Sedimentation equilibrium experiments on the polypeptide R-Thr in guanidine hydrochloride solutions indicated homogeneity with respect to molecular weight; however, the molecular weight value 31,400 indicates that the polypeptide R-Thr exists as a dimer in guanidine hydrochloride solutions. Sedimentation equilibrium experiments on the polypeptide R-Thr in urea solutions and in dilute salt solutions containing sodium dodecyl sulfate indicated heterogeneity with respect to molecular weight and weight- average molecular weights of approximately 20,000. © 1968, American Chemical Society. All rights reserved.