Occurrence of disialosyl groups in glycoproteins

The occurence of disialosyl (α-N-acetylneuraminyl-(2→8)-N-acetylneuraminyl) groups in glycoproteins was studied. It was found by methylation analysis that 8.5 % of N-acetylneuraminic acid in brain glycoproteins was substituted at C-8. The corresponding value was 16.6 % in brain gangliosides. The substituent was identified as neuraminic acid from its lability to neuraminidase treatment. The results demonstrate that not only gangliosides contain disialosyl groups, but these are also found in glycoproteins. The group is present in several types of carbohydrate units, with the highest proportion in N-glycosidic chains of large molecular size.