A Comparison of Glycopeptides Derived from Soluble and Insoluble Collagens

Digestion of preparations of insoluble collagen of guinea pig skin with collagenase and trypsin led to the production of two distinct glycopeptide fractions. The lower molecular weight fraction was similar in amount and in composition to the single predominant glycopeptide fraction obtained by similar treatment of soluble collagen. The major component in this fraction had the same chemical and physical characteristics as the glycohexapeptide, Gly-Met-Hyl(-Gal-Glc)-Gly-His-Arg, which had been characterized previously in similar digests of soluble collagen. The second and higher molecular weight glycopeptide fraction (which contained no hydroxylysine) was found only in insoluble collagen. The major amino acids and carbohydrates present in this fraction were aspartic and glutamic acids, glycine, alanine, serine, proline, glucose, galactose, mannose, glucosamine, galactosamine, and sialic acid. The fraction appeared to be quite heterogeneous, and it has not yet been possible to establish whether interpeptide crosslinks were present. This fraction was, however, increased in samples of perchlorate-insoluble collagen identical with those in which Hormann reported evidence for covalent cross-links involving carbohydrate. Alkaline hydrolysis of soluble or insoluble collagen led to the isolation of closely similar quantities of both O-Hyl-(-Gal-Glc) and O-Hyl(-Gal), thus establishing the presence of limited numbers of monosaccharide side chains in both forms of collagen. These analyses, as well as studies of partial acid hydrolysates of purified hydroxylysine-containing glycopeptides, showed the presence in mammalian skin collagen of a disaccharide in which C-1 of D-glucose is linked to D-galactose, and C-1 of D-galactose to the δ-hydroxyl group of hydroxylysine. No evidence was found for the participation of this carbohydrate prosthetic group in crosslinking related to the conversion of soluble collagen to insoluble collagen.