The periodate-degradation technique was used to demonstrate the mechanism by which the reducible cross-links of collagen are stabilized. In all the tissues examined, Smith degradations of the 3H-labelled cross-links indicated that dihydroxylysinonorleucine is derived solely from hydroxylysino-5-oxonorleucine, the Amadori-rearranged product of the original condensation reaction. Monohydroxylysinonorleucine exists in both keto and aldimine forms, the former being derived from hydroxyallysine and the latter from allysine. Their relative proportions are tissue-dependent and are related to the degree of hydroxylation of the specific lysine residues in both the telopeptides and the triple helix.
