Quantitative cleavage of the N-glycosidic bond under the normal conditionsof methanolysis used for the analysis of glycoprotein monosaccharides

The most common method used for the liberation of monosaccharides from glyc oprotein N-glycans involves anhydrous methanolysis because it liberates alm ost quantitatively monosaccharides as O-methylglycosides, which are resista nt to further degradation, However, it is generally assumed that this metho d does not cleave quantitatively the N-glycosidic bonds. This paper demonst rates that classical methanolysis conditions quantitatively cleave the N-gl ycosidic bond (96%), liberating glucosamine (and not its O-methylglycosides ) and other minor reaction products which were identified. Because other N- acetyl-D-glucosamine (GlcNAc) residues are quantitatively liberated as the O-methylglycosides of glucosamine, the GlcNAc residue involved in the N-gly cosidic bond is separated from the others using gas chromatography of hepta fluorobutyrate derivatives. (C) 1999 Academic Press.