d‐Galactofuranose in the N‐linked sugar chain of a glycopeptide from Ascobolus furfuraceus

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Abstract
Two types of linkages between the carbohydrate and the peptide moiety in the glycopeptide from Ascobolus furfuraceus are described. Treatment with mild alkali produced .beta.-elimination of a small oligosaccharide. Evidence for the O-glycosidic linkage was provided by (a) increase in absorbance at 240 nm, (b) decrease in threonine and serine content after the alkaline treatment and (c) detection of tritiated oligosaccharide following alkaline NaB3H4 reduction. Mannose is the sugar involved in the O-glycosidic linkage. The remaining glycopeptide was branched by galactofuranose units, which were selectivity released by mild acid hydrolysis. The N-glycosidic linkage of the sugar chain was conclusively proved by cleavage with endo-.beta.-N-acetyl-glucosaminidase. Sequential NaB3H4 reduction and acid hydrolysis gave [3H]glucosaminitol. The structure of the sugar chain was studied by 13C NMR spectroscopy and by methylation analysis.