Covalent structure of collagen: amino acid sequence of five consecutive cyanogen bromide peptides from type III collagen of human liver

Abstract

Type III collagen was solubilized from human liver by limited pepsin digestion and purified by differential salt precipitation and carboxymethylcellulose chromatography. Digestion with cyanogen bromide yielded the 9 distinct peptides previously described and an additional tripeptide not recognized in earlier studies. Five of these peptides, .alpha.1(III)-CB1, 2, 4, 8 and 10, were further purified by molecular sieve and/or ion exchange chromatography. They contained 12, 40, 149, 125 and 3 amino acid residues, respectively. The amino acid sequence of these peptides was determined by automated Edman degradation of tryptic (before and after maleylation), chymotryptic, thermolytic or hydroxylamine-derived peptide fragments as well as the intact peptides. The alignment of these 5 peptides within the collagen chain is deduced to be 1-8-10-2-4 by homology with known .alpha.1(I) sequences. The known CNBr peptide alignment of the NH2-terminal portion of type III collagen so far would, therefore, be .alpha.1(III)-CB3-7-6-1-8-10-2-4 and correspond to the homologous region of .alpha.1(I)-CBO-1-2-4-5-8-3 or residues 11-567 of the .alpha.1(III) collagen chain.