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

The association constant between a protein and a carbohydrate can be determ ined based on the relationship between the delay of migration time of a pro tein as sample and the concentration of a ligand as additive in capillary z one electrophoresis. In this determination the carbohydrate as ligand must have an electric charge to enable accurate estimation of the migration dela y caused by the ligand. This paper proposes a convenient method for convers ion of neutral carbohydrates having no electric charge to derivatives havin g a strongly negative charge. It is based on dithioacetalation with 2-merca ptoethanesulfonate in trifluoroacetic acid. The derivatization is rapid and almost quantitative at room temperature, and does not cause cleavage of in terglycosidic linkages between hexose residues nor removal of the sialic ac id residue. This paper demonstrates the usefulness of the proposed method f or the determination of the association constants of neutral carbohydrates to proteins, using simple oligosaccharides and lectins as models. (C) 1999 Elsevier Science B.V. All rights reserved.