Relationship between the intra and intermolecular cross-links of collagen.

Spontaneous cross-linking in vitro, during incubation of purified collagen in nonstriated and native type fibrils, was studied to elucidate the relationship between intra and intermolecular cross-links. In nonbanded fibrils, the aldol condensation products of two allysyl residues, previously shown to constitute the intramolecular cross-link, formed spontaneously and could be isolated as such, whereas in native type fibrils, these compounds were found to be incorporated into an intermolecular cross-link; after chemical reduction they could not be isolated. Similar results were obtained from studies on a native collagenous tissue, rat tail tendon. It is suggested that the intramolecular cross-link is not a separate entity but only an intermediate of an intermolecular cross-link and that its existence in solubilized collagen is a result of the extraction procedure. The quantitative formation of intramolecular cross-links in vitro and identification of the cross-link compound are also reported.