A mouse submandibular sialomucin containing both N- and O-glycosylic linkages

A sialomucin from mouse submandibular glands was treated with mild base-Me2SO. This treatment cleaves O-glycosylically linked oligosaccharides, but preserves the integrity of the protein core. After treatment with mild base-Me2SO, 49.2% (by weight) of the oligosaccharides were removed from the polypeptide; they were composed of residues of 2-acetamido-2-deoxy-D-glucose, 2-acetamido-2-deoxy-D-galactose, sialic acid, and D-galactose. These oligosaccharides were linked O-glycosylically via 2-acetamido-2-deoxy-D-galactose. Chromatography of the base-Me2SO-treated mucin on Sephacryl S-300 indicated that the protein core, with its base-resistant oligosaccharides, is a single, high-molecular-weight species. The mild-base-resistant linkages remaining on the protein core (50.8% of the total carbohydrates by weight) also contained D-mannose. The presence of these mild-base-resistant linkages, and the formation of 2-acetamido-2-deoxy-D-glucitol following treatment with M NaOH-M NaBH4, confirmed the presence of N-glycosylic linkages.