Structural studies of the acidic oligosaccharide units from bovine glycophorin

Abstract

The O-glycosidically-linked carbohydrate units of glycophorin from bovine erythrocyte membrane were released by alkaline borohydride treatment. These oligosaccharides were separated into the neutral fractions and the acidic fractions by ion-exchange chromatography followed by gel filtration. The two acidic fractions (fractions 10 and 13) which have the smallest molecular weight in acidic oligosaccharides, were further purified by gel filtration on Bio-Gel P-4 column. Two acidic oligosaccharides (fractions 10-I and 10-II), heptasaccharides, were separated by gel filtration on a Bio-Gel P-4 column from fraction 10. These structures were determined by methylation analyses, nitrous acid deamination after hydrazinolysis and Smith degradation after desialylation. In addition, the structures were also analyzed by direct-probe mass spectrometry of the permethylated derivatives before and after desialylation. These studies indicated that one of them (fraction 10-I) was NeuNGc alpha(2 leads to 3)Gal beta(1 leads to 4)GlcNac beta(1 leads to 3)Gal beta(1 leads to 4)GlcNAc beta (1 leads to 3)Gal beta(1 leads to 3)GalNAcol and another heptasaccharide (fraction 10-II) was Gal beta (1 leads to 4)GlcNAc beta (1 leads to 3)Gal beta (1 leads to 3)[NeuNGc alpha(2 leads to 3)Gal beta(1 leads to 4)GLcNAc beta(1 leads to 6)]GalNAcol. Although another acidic fraction (fraction 13, was obtained as a single peak on a Bio-Gel P-4 column, it appeared to be the mixture of a heptasaccharide, NeuNGc alpha(2 leads to 3)Gal beta(1 leads to 4)GlcNAc beta(1 leads to 3 or 6)[Gal beta (1 leads to 4)GLcNAc beta (1 leads to 6 or 3)]Gal beta (1 leads to 3)GalNAcol and an oligosaccharide similar to fraction 10-II, by analysis of two products obtained by Smith degradation after desialylation.