Structures of the sugar chains of mouse immunoglobulin G

The asparagine-linked sugar chains of mouse immunoglobulin G (IgG) were quantitatively liberated as radioactive oligosaccharides from the polypeptide portions by hydrazinolysis followed by N-acetylation, and NaB³H₄ reduction. After fractionation by paper electrophoresis, lectin (RCA120) affinity high-performance liquid chromatography, and gel filtration, their structures were studied by sequential exoglycosidase digestion in combination with methylation analysis. Mouse IgG was shown to contain the biantennary complex type sugar chains. Eight neutral oligosaccharide structures, viz, ±Galβ1 → 4GlcNAcβ1 → 2Manα1 → 6(±Galβ1 → 4GlcNAcβ1 → 2Manα1 → 3)Manβ1 → 4GlcNAcβ1 → 4(±Fucα1 → 6)GlcNAc, were found after the sialidase treatment. The molar ratio of the sugar chains with 2, 1, and 0 galactose residues was 2:5:3. The galactose residue in the monogalactosylated sugar chains was distributed on Manα1 → 3 and Manα1 → 6 sides in the ratio of 1:3. The oligosaccharides were almost wholly fucosylated and contained no bisecting N-acetylglucosamine which is present in human, rabbit, and bovine IgGS.