STRUCTURE OF THE N-GLYCANS AND O-GLYCANS OF THE A-CHAIN OF HUMAN PLASMA ALPHA-2HS-GLYCOPROTEIN AS DEDUCED FROM THE CHEMICAL-COMPOSITIONS OF THE DERIVATIVES PREPARED BY STEPWISE DEGRADATION WITH EXOGLYCOSIDASES

The structure of the glycans of the A-chain of human plasma alpha2HS-glycoprotein was established from the chemical compositions of its derivatives prepared by sequential enzymatic, degradation of the carbohydrate moiety, from the determination of the kind and amount of the monosaccharides liberated after each step of the enzymatic digestion, and from the distinct specificity of the highly purified exoglycosidases. The exoglycosidases were three sialidases (Vibrio cholerae, fowl plague virus, and Arthrobacter ureafaciens), two beta-galactosidases (Streptococcus pneumoniae and bovine testis), one alpha-N-acetylgalactosaminidase, one beta-N-acetylglucosaminidase, and one alpha-mannosidase. Utilizing sialidases with different cleavage specificities, the number of alpha2-3- and alpha2-6-linked sialic acid residues could be separately determined. As to the beta-galactosidases, the enzyme isolated from S. pneumoniae cleaves only beta1-4-linked galactose residues, whereas the bovine testes enzyme acts on both the beta1-4- and beta1-3-linked galactose residues. Jack bean beta-N-acetylglucosaminidase cleaves beta1-2, beta1-4, and beta1-6 GlcNAc with higher activity for the beta1-2. Jack bean alpha-mannosidase cleaves alpha1-2, alpha1-6, and alpha1-3 Man with greater activity for alpha1-2 and alpha1-6. Bovine liver alpha-N-acetylgalactosaminidase cleaves O-linked GalNAc. On the basis of these results, the A-chain of alpha2HS-glycoprotein was found to possess two biantennary N-glycans and two O-linked trisaccharides.