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 c arbon 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 electr odes with the adsorbed enzyme produced anodic currents for the electro catalytic oxidation Of D-gluconate. Neither electron transfer mediator s 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 electr ocatalysis. The current-potential curve for the catalytic oxidation re action has an unusual shape, starting at - 0. 14 V with a hump at abou t 0.02-0.05 V vs. Ag/AgCl. A steady state current was obtained at fixe d electrode potentials and the current increased with increasing conce ntrations of the substrate to approach saturation. The results could b e described by an equation of direct bioelectrocatalysis at an electro de coated with an enzyme. A probable candidate for the redox site of t he enzyme that donates electrons to the electrode was heme c.