Capillary electrophoretic determination of the association constant of a protein and a neutral carbohydrate by introducing mercaptoethanesulfonate tags to the carbohydrate

Abstract

The association constant between a protein and a carbohydrate can be determined based on the relationship between the delay of migration time of a protein as sample and the concentration of a ligand as additive in capillary zone electrophoresis. In this determination the carbohydrate as ligand must have an electric charge to enable accurate estimation of the migration delay caused by the ligand. This paper proposes a convenient method for conversion of neutral carbohydrates having no electric charge to derivatives having a strongly negative charge. It is based on dithioacetalation with 2-mercaptoethanesulfonate in trifluoroacetic acid. The derivatization is rapid and almost quantitative at room temperature, and does not cause cleavage of interglycosidic linkages between hexose residues nor removal of the sialic acid residue. This paper demonstrates the usefulness of the proposed method for the determination of the association constants of neutral carbohydrates to proteins, using simple oligosaccharides and lectins as models.