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

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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.