Studies on the carbohydrate-protein linkage region in bovine corneal keratan sulfate. II. Structural studies on linkage region-enriched neutral glycopeptides.

In order to elucidate the chemical structure of the carbohydrate-protein linkage region of bovine corneal keratan sulfate, glycopeptides which had been highly enriched in the linkage region under mild conditions were subjected to glycosidase digestion in combination with methylation analysis. After removal of the peripheral N-acetylglucosamine and galactose residues by exhaustive glycosidase digestion, the residual glycopeptide (GP-A) was found to contain 0.6 mol of fucose, 3 mol of mannose, and 2 mol of N-acetylglucosamine per mol. GP-A was then serially digested with exoglycosidases, and the released sugars and the composition of the residual glycopeptides isolated by gel filtration were analyzed by gas-liquid chromatography. Further, the dansyl derivative of GP-A was digested with endo-beta-N-acetylglucosaminidase D and the products were analyzed to explore the location of the fucose residue. The results obtained, combined with those from methylation analysis of all the glycopeptides, revealed that the carbohydrate structure of the linkage region and its environs of corneal keratan sulfate is as follows. (Formula: See Text).