The carbohydrate associated with the collagen fibres of cartilage

The present study was undertaken with a view to establishing the qualitative and quantitative distribution of the carbohydrate moiety (or moieties) reported to be associated with the collagen fraction in cartilage. The study was extended to compare the collagenous fractions from both immature (embryonic) and mature cartilage tissue, in order to test the hypothesis invoking a role for one or more of these components in the ultimate organization of the extracellular collagen framework. Results of the present study show that the hexoses of youngbovine nasal cartilage residue (YBNCR) are distributed in the following manner: Over 40% are found in the hydroxylysine linked carbohydrate units consisting of glucosylgalactosylhydroxylysine and galactosylhydroxylysine in a ratio of 2:1. About 7% of the hexoses are associated with a collagen-linked heterosaccharide unit. The rest are accounted for by the keratan sulphate and chondroitin sulphate of proteoglycan. The hydroxylysine linked carbohydrate units are located in highly cross-linked regions of collagen whereas the trypsin susceptible, less ordered part of collagen contains the heterosaccharide moiety. The component sugars of the heterosaccharide are mannose, galactose, glucose and glucosamine with smaller quantities of fucose, galactosamine and sialic acid. The amino acid residue likely to be involved in the peptide-carbohydrate linkage is either aspartic or glutamic acid (or their amides). No such collagen linked heterosaccharide is present in the embryonic bovine nasal cartilage residue (EBNCR). The EBNCR also differs from the YBNCR in that it contains much less proteoglycan and noncollagenous protein. Trypsin causes much more extensive degradation and solubilization of the collagen fibres in EBNCR. Glucosylgalactosylhydroxylysine appears to be the predominant hydroxylysine linked carbohydrate unit in embryonic cartilage.