Increased lysine hydroxylation in rat bone and tendon collagen and localization of the additional residues

Abstract

The α1 and α2 chain obtained from guanidine extracts of rat bone collagen contain 10 and 6 additional hydroxylysine residues, in comparison to the respective α chains of rat skin collagen. An increase was also demonstrated for insoluble bone collagen. At least for the α1 chains, no evidence was obtained for a corresponding increase in carbohydrate content. Hydroxylysine values intermediate between those of skin and bone are found for the α2 chain of rat tail tendon collagen, yet the α1 chain is in this respect indistinguishable from that of skin. The relationship of the α chains of rat bone to type I collagen was demonstrated by CNBr cleavage and characterization of most of the fragments. This approach also allowed the localization of the additional hydroxylysine residues in three nonhelical cross-linking regions, as well as in various sites of the helical sequence. The findings do not support the idea that glycine in a position adjacent to the carboxyl group of lysine is an absolute requirement for hydroxylation.