Isolation of a Crosslinked Cyanogen‐Bromide Peptide from Insoluble Rabbit Collagen Tissue Differences in Hydroxylation and Glycosylation of the Crosslink

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Abstract
A radioactive peptide was isolated from CNBr digests of sodium boro[3H]-hydride-reduced collagen from rabbit bone, tendon and skin. It was identified as a crosslinked peptide linking the short C-terminal CNBr peptide .alpha.1-CB6B (17 amino acid residues) to .alpha.1-CB5 (37 residues) from the helical part of the chain of an adjacent molecule. Both peptides could be separated after cleaving the crosslink with periodate. The crosslinked peptide .alpha.1-CB5 .times. .alpha.1-CB6B originates from an intermolecular crosslink between quarter-staggered molecules within collagen fibrils previously assigned as head-to-tail link. The chemical nature of the reduced crosslinking component was identified and was shown to differ between peptides derived from different tissues: .alpha.1-CB6B .times. .alpha.1-CB5 from bone contains hydroxylysinohydroxynorleucine [o5Lys(o5.omega.Nle)] whereas the skin peptide contains hydroxylysinonorleucine [o5Lys(.omega.Nle)]. The peptide derived from tendon contains both components. The relation of o5Lys(.omega.Nle) to o5Lys(o5.omega.Nle) in the peptides corresponds to that of the original tissue. Histidino-hydroxymerodesmosine, which is a major reduced crosslinking component in skin and tendon, is completely absent in the isolated peptides. The crosslinking component in the skin peptide is completely glycosylated, mainly by glucosyl-galactosyl residues and to a smaller extent by galactosyl residues. o5Lys(o5.omega.Nle) from the bond peptide is only partly glycosylated, containing equal amounts of the disaccharide and monosaccharide. Only slight glycosylation was found in the tendon peptide.