Methylation Techniques in the Structural Analysis of Glycoproteins and Glycolipids

Abstract

Publisher Summary This chapter describes the methylation techniques used in the structural analysis of glycoproteins and glycolipids. The methylation reaction can be directly applied to the analysis of glycolipids, whereas glycoproteins are not generally methylated directly due to their low solubility in dimethyl sulfoxide. The carbohydrate moiety of the glycoprotein is first isolated as a glycopeptide after extensive proteolytic digestion, or as a reduced oligosaccharide after treatment with alkaline sodium borohydride. Completeness of the methylation reaction is a prerequisite for successful methylation analysis. The critical step in the permethylation procedure is the generation of the sugar alkoxides catalyzed by methylsulfinyl carbanion. It is to be expected that the extensive formation of the alkoxide species has occurred if an excess of the carbanion can still be detected in the mixture after the carbohydrates have reacted. Commercial tert -butoxide salt can be dissolved in dimethyl sulfoxide without any further steps. When this method is used, the intensities of the nonsugar signals in gas liquid chromatography (GLC) tend to be lowering than those seen when the reagent is prepared with the aid of sodium hydride. Methanolysis is also preferred in the analysis of N -acetyl- and N -glycolylneuraminic acid residues, which are commonly found in animal glycolipids and glycoproteins. The quantitation of the methylated monosaccharides is also elaborated in the chapter.