Structural studies of the sugar chains of cold-insoluble globulin isolated from human plasma

The asparagine-linked sugar chains of cold-insoluble globulin isolated from human plasma were released as oligosaccharides from the polypeptide moiety by hydrazinolysis. These oligosaccharides were N-acetylated and could be labeled by reduction with NaB[3H]4. The yield of radioactive oligosaccharides indicated that the glycoprotein has four asparagine-linked sugar chains in one molecule. More than 90% of the radioactive oligosaccharides contain N-acetylneuraminic acid, and could be separated into two acidic oligosaccharides, A-1 and A-2. By sequential exoglycosidase digestion in combination with methylation studies, their structures were elucidated as Gal beta 1 leads to 4GlcNAc beta 1 leads to 2Man alpha 1 leads to 6(NeuAc alpha 2 leads to 6Gal beta 1 leads to 4GlcNAc beta 1 leads to 2Man alpha 1 leads to 3) Man beta 1 leads to 4GlcNAc beta 1 leads to 4GlcNAc and NeuAc alpha 2 leads to 6Gal beta 1 leads to 4GlcNAc beta 1 leads to 2Man alpha 1 leads to 6 (NeuAc alpha 2 leads to 6Gal beta 1 leads to 4GlcNAc beta 1 leads to 2 Man alpha 1 leads to 3)-Man beta 1 leads to 4GlcNAc beta 1 leads to 4GlcNAc.