Structure of the linkage-region between polysaccharide chain and core protein in bovine corneal proteokeratan sulfate.

Peptidokeratan sulfate from bovine cornea was degraded by a combination of desulfation, exo-enzymic digestion and finally digestion with endo-beta-N-acetylglucosaminidase D. The same procedure was carried out both with [3H]fucose-labelled and [3H]mannose-labelled peptidokeratan sulfate. Data obtained by methylation analysis of peptidokeratan at the different degradation steps, as well as action of endo-beta-N-acetylglucosaminidase D, showed that the binding-region in proteokeratan sulfate from bovine cornea is identical with a structure found in various GlcNAc(beta 1-N)-Asn-linked mannosyl glycoproteins. The existence of a chitobiose unit between asparagine and mannose was proved by action of endo-beta-N-acetylglucosaminidase D. The existence and position of an (alpha 1 leads to 6)-linked fucosyl residue at the Asn-bound GlcNAc was demonstrated by action of alpha-fucosidase, endo-beta-N-acetylglucosaminidase D and by gel chromatography on Bio-Gel P-4. By gas chromatography/mass spectrometry studies, the existence of a 1,4,6-trisubstituted beside a 1,4-disubstituted GlcNAc in the binding-region oligosaccharide was shown. Other results reported here are according to analytical data previously published (Keller, R., Stein, T., Stuhlsatz, H.W., Greiling, H., Ohst, E., Müller, E. & Scharf, H.-D. (1981) Hoppe-Seyler's Z. Physiol. Chem. 362, 327-336).