Covalent structure of collagen: amino acid sequence of cyanogen bromide peptides from the amino-terminal segment of type III collagen of human liver.

Human liver type III collagen was prepared by limited pepsin digestion, differential salt precipitation, and carboxymethylcellulose chromatography. Cyanogen bromide digestion of purified type III collagen chains yielded nine distinct peptides. Three peptides, alpha1(III)-CB3, alpha1(III)-CB7, and alpha1(III)-CB6, were isolated by carboxymethylcellulose chromatography and Sephadex G-50 SF gel filtration. Automated Edman degradation together with selective hydroxylamine cleavage and chymotrypsin and trypsin digestion enabled determination of their complete amino acid sequence. Compared with type I collagen, the data show tentative homology of alpha1(III)-CB3 with alpha1(I)-CB1, alpha1(I)-CB2, and alpha1(I)-CB4; alpha1(III)-CB7 with alpha1(I)-CB5; and alpha1(III)-CB6 with the amino-terminal portion of alpha1(I)-CB8. Close interspecies homology was found between the sequences presented here with 90 residues of alpha1(III)-CB3 and 26 of alpha1(III)-CB8 of calf aorta. The present study establishes the amino acid sequence of 229 residues near the amino terminus or nearly one-quarter of the type III collagen chains. The disaccharide, Glc-Gal, was convalently bound to hydroxylysine at a position corresponding to the same location in the alpha1(I) chain.