Structural studies on the carbohydrate units of armadillo submandibular glycoprotein

The structure of carbohydrate units of the major glycoprotein fraction of armadillo submandibular gland was investigated. Alkaline borohydride reductive cleavage of the glycoprotein resulted in the release of O-glycosidically linked mono- and disaccharide units. The monosaccharide was identified as N-acetylgalactosaminitol, whereas disaccharide contained of N-acetylneuraminic acid and N-acetylgalactosaminitol. Treatment of the native and desialyzed glycoprotein with alpha-N-acetylgalactosaminidase resulted in the removal of 60% and 96% of N-acetylgalactosamine, respectively. No cleavage of this sugar was affected by the action of beta-N-acetylhexosaminidase. Both N-acetylgalactosamine and N-acetylneuraminic acid were susceptible to oxidation with periodate. Analyses of the partially methylated N-acetylgalactosamine derivatives, obtained from the permethylated native glycoprotein, showed the presence of 3,4,6-tri-O-methyl-N-methylacetamidogalactose and 3,4-di-O-methyl-N-methylacetamidogalactose in a ratio of 1 : 0.4. Only 3,4,6-tri-O-methyl-N-methylacetamidogalactose was found in the hydrolysates of permethylated desialyzed glycoprotein. These results together with our previous data on chemical composition of the glycoprotein suggest that about 30% of the oligosaccharide chains consist of NeuAc alpha 2 leads to 6GalNAc alpha 1 leads to O-Thr(Ser) and 70% of GalNAc alpha leads to O-Thr(Ser).