Comparative study of the carbohydrate moieties of rat and human plasma alpha 1-acid glycoproteins

Rat and human alpha 1-acid glycoproteins contain 5 and 6 acidic asparagine-linked sugar chains in 1 molecule, respectively. The structures of these sugar chains were studied by sequential exoglycosidase digestion in combination with methylation analysis after being released from the polypeptide back bone by hydrazinolysis. All oligosaccharides obtained from both glycoproteins contain N-acetylneuraminic acid. Sialidase digestion of the acidic oligosaccharides from rat sample released three biantennary complex type sugar chains and three triantennary complex type sugar chains, the outer chains of which are composed of Gal beta 1 leads to 3GlcNAc and/or Gal beta 1 leads to 4GlcNAc. In the original acidic oligosaccharides, sialic acids occur as three type linkages: NeuAc alpha 2 leads to 3Gal, NeuAc alpha 2 leads to 6Gal, and Gal beta 1 leads to 3(NeuAc alpha 2 leads to 6)GlcNAc. In addition to the five sugar chains reported by Fournet, B., Montreuil, J., Strecker, G., Dorland, L., Haverkamp, J., Vilegenthart, J. F. G., Binette, J. P., and Schmid, K. ((1978) Biochemistry 17, 5206-5214), the structures of three new sugar chains of human alpha 1-acid glycoprotein were elucidated.