ENZYME-CATALYZED ELECTROCHEMICAL OXIDATION OF D-GLUCONATE AT ELECTRODES COATED WITH D-GLUCONATE DEHYDROGENASE, A MEMBRANE-BOUND FLAVOHEMOPROTEIN

D-gluconate dehydrogenase was dip coated onto ordinary electrodes of carbon paste, glassy carbon, pyrolytic graphite, gold, silver, platinum or mercury. Surface redox waves clearly attributable to the reaction of the adsorbed enzyme were not observed. Nevertheless, all the electrodes with the adsorbed enzyme produced anodic currents for the electrocatalytic oxidation Of D-gluconate. Neither electron transfer mediators nor promoters were necessary. The adsorbed enzyme was stable enough at pH 5.0 and at 5-degrees-C to allow the quantitative study of electrocatalysis. The current-potential curve for the catalytic oxidation reaction has an unusual shape, starting at - 0. 14 V with a hump at about 0.02-0.05 V vs. Ag/AgCl. A steady state current was obtained at fixed electrode potentials and the current increased with increasing concentrations of the substrate to approach saturation. The results could be described by an equation of direct bioelectrocatalysis at an electrode coated with an enzyme. A probable candidate for the redox site of the enzyme that donates electrons to the electrode was heme c.