Cyclic voltammetric studies of carbohydrate-protein interactions on gold surface

A simple electrochemical method for the determination of association constants between carbohydrates and carbohydrate-binding proteins using cyclic voltammetry (CV) is described. The binding of concanavalin A (Con A) and cholera toxin (CT) to their specific α-mannose and β-galactose derivatives self-assembled on gold electrodes is electrochemically monitored with a redox probe of K₃Fe(CN)₆/K₄Fe(CN)₆. Upon binding of the proteins to the carbohydrate-modified electrodes, the redox current in CV decreases. The binding-induced change in electrochemical signal is thus used to construct Langmuir adsorption isotherm for the carbohydrate-protein interactions and to obtain the association constants. The association constants of carbohydrate-protein interactions determined by CV ((5.8 ± 1.2) × 10⁷ M^{- 1} for mannose-Con A, (2.6 ± 0.5) × 10⁸ M^{- 1} for galactose-CT) were in good agreement with those measured with electrochemical impedance spectroscopy and quartz crystal microbalance.