Structures and Immunochemical Properties of Oligosaccharides Isolated from Pig Submaxillary Mucins

Abstract

Abstract Two immunochemically distinct mucins have been isolated from pig submaxillary glands. The glands were combined according to the ability of aqueous extracts of these glands to inhibit hemagglutination of human type A erythrocytes. Mucin isolated from the glands containing blood group A activity is designated A+ pig submaxillary mucin (A+-PSM), while mucin isolated from the remaining glands is designated A- pig submaxillary mucin (A--PSM). The carbohydrate composition of both mucins is similar and comprises N-acetylgalactosamine, fucose, galactose, and N-glycolylneuraminic acid. Treatment of these mucins with alkaline borohydride resulted in the release of a series of reduced oligosaccharides and the monosaccharide, 2-acetamido-2-deoxy-d-galactitol (N-acetylgalactosaminitol). Conditions are reported which give more than 90% cleavage of the sugar residues from the protein chain. The most complex oligosaccharide (designated oligosaccharide I) was a pentasaccharide, 2-acetamido-2-deoxy-α-d-galactopyranosyl (1 → 3)-[α-l-fucopyranosyl-(1 → 2)]-β-d-galactopyranosyl-(1 → 3)-[N-glycolylneuraminyl-(2 → 6)]-2-acetamido-2-deoxy-d-galactitol. In addition, the following oligosaccharides were isolated (structures are given as related to oligosaccharide I): oligosaccharide II, I minus N-acetylgalactosamine; oligosaccharide III, a disaccharide N-glycolylneuraminyl → N-acetylgalactosaminitol; oligosaccharide IV, I minus N-glycolylneuraminic acid; oligosaccharide V, II minus N-glycolylneuraminic acid. N-Acetylgalactosaminitol (Fraction VI) was the only detectable monosaccharide. Rabbit antiserum to human type A erythrocyte stroma precipitated A+-PSM, but not A--PSM. Oligosaccharides I and IV, found only in A+-PSM, are potent inhibitors of the anti A-A+-PSM precipitation, but oligosaccharides II, III, and V and a monosaccharide (Fraction VI) are completely inactive.