Biosynthesis of the Intramolecular Cross-links in Rat Skin Collagen

Abstract The present study attempts to analyze the nature of the intramolecular cross-linking in rat skin collagen. A new procedure is described for the isolation of a cross-linking peptide from rat skin collagen. The procedure is also useful for the separation of similar peptides from other collagen species. The peptide obtained from rat skin collagen contains the α,β unsaturated aldehyde as 2,4-dinitrophenylhydrazone, is devoid of lysine, but when prepared from young animals that received 14C- and 3H-labeled lysine it is radioactive. In two different experiments the 14C specific activity of the peptide (expressed as disintegrations per min per µmole of aldehyde) was twice the specific activity of collagen lysine, suggesting that two modified lysines are involved in the cross-link. The percentage of retention of 3H in the peptide obtained from collagen labeled with l-lysine-14C, uniformly labeled, and dl-lysine-6-3H strongly suggests that the aldehyde is formed by removal of the e-amino group of lysine and that the cross-link is formed by an aldol-like condensation of two aldehydes from adjacent chains. Similar experiments with the same 14C-labeled lysine and dl-lysine-4,5-3H add support to this possibility. Both experiments are also suggestive of the loss of a single tritium from position 5 of lysine during hydroxylation, as has already been reported.