Isolation and characterization of a double chain intermolecular cross-linked peptide from insoluble calf bone collagen.

A double chain peptide containing the sodium borohydride-reduced intermolecular cross-link, hydroxylysinohydroxynorleucine, was isolated following sequential cyanogen bromide digestion and limited alkaline hydrolysis of insoluble calf bone collagen. Amino acid composition and NH2-terminal sequence analysis indicated that the peptide was highly acidic and consisted of 19 amino acid residues including the cross-link. Amino acid composition and automated sequence analysis of this peptide before and after cleavage of the cross-link, using periodic acid, provided the data from which the following structure was deduced. (formula: see text). The sequence of the larger peptide is identical with that of residues 8c to 19c in the COOH-terminal nonhelical region of the homologous skin collagen alpha1 chain. The hydroxylysine residue located at position 17c in the alpha chain of type I collagen appears to be a predominant site for intermolecular cross-link formation. Assignment of the smaller peptide component within the known primary structure of the collagen molecule currently cannot be made.