The linkage of teleost skin keratan sulfate to protein was investigated. Afeter its exhaustive digestion with pronase, peptidokeratan sulfate was obtained with aspartic acid as the predominant amino acid. The N-terminal of the amino acid residues of the preparation was dansylated, and the carbohydrate-peptide linkage fragment was isolated, with the aid of fluorescence, by sequential digestion with Flavobacterium endo-β-galactosidase, β-galactosidase, β-N-acetylhexosaminidase and endo-β-N-acetylglucosaminidase D, followed by Bio-Gel p-4 column chromatography. The structure of the dansylated fragment thus obtained was identified dansylated asparaginyl N-acetyl-D-glucosamine. Treatment of the dansylated keratan sulfate peptide with almond glycopeptidase, which specially cleaves thet asparaginyl N-acetyl-D-glucosamine linkage in the glycoproteins, also showed asparaginyl N-aceytyl-D-glucosamine linkage to be in the core region of this keratan sulfate. We conclude that teleost skin keratan sulfate is bound to protein via an N-glycosyl linkage between N-acetyl-D-glucosamine and asparagine. The keratan sulfate core apparently consist of trimannosyl-N,N′-diacetylchitobiose units, considering the specificity of endo-β-N-acetylglucosaminidase D.
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