Nonenzymatic Glucosylation of Lysyl and Hydroxylysyl Residues in Type I and Type II Collagens

Nonenzymatic glucosylation of type I and type II collagens was examined by incubating collagen substrates with D-glucose in vitro. In one set of experiments, unlabeled collagen was incubated with [14C]-glucose and the incorporation of [14C]-radioactivity into protein was determined by TCA precipitation. The incorporation was dependent on the concentration of glucose and the time of incubation. The glucosylated product was also examined by SDS-polyacrylamide slab gel electrophoresis. The results indicated that both α1 (I)- and α2(I)-chains of type I collagen were glucosylated and the glucosylation occurred both with native and denatured collagen as substrate. In further studies [3H]-lysine-labeled collagens were glucosylated, the products reduced by NaBH4, and the [3H]-lysine-derived residues were separated by amino acid analyzer. After a 144 h incubation in vitro, 18.9 % of [3H]-lysyl residues and 36.5 % of [3H]-hydroxylysyl residues in type I collagen were substituted with glucose. In contrast, 47.9 % of [3H]-lysyl residues and 68.1 % of [3H]-hydroxylysyl residues in type II collagen were glucosylated after 144 h incubation. Based on quantitative amino acid analyses of the substrates, these values represent 27.6 lysine plus hydroxylysine residues substituted per triple-helical type I collagen molecule and 65.3 residues per triple-helical type II collagen molecule. Thus, type I and type II collagens display differential susceptibilities to nonenzymatic glucosylation. Finally, [3H]-proline-labeled type I collagen was glucosylated to varying extents, and the glucosylated products were used as substrates for human polymorphonuclear leukocyte collagenase. No difference in susceptibility to this collagenase was noted, irrespective of the extent of glucosylation.