ENZYME-SUBSTRATE KINETICS OF ADSORBED CYTOCHROME-C PEROXIDASE ON PYROLYTIC-GRAPHITE ELECTRODES

Cytochrome c peroxidase (CCP) adsorbed at (sub)monolayer surface coverage on edge-oriented pyrolytic graphite (EPG) is being used as a model system for determining the effects of immobilization on the kinetic properties of an-enzyme and for developing molecular insight into enzymatic electrocatalysis. Evidence indicating that the catalytic reduction of H2O2 at the CCP/EPG electrode occurs via the intact enzyme and not via some form of ''free'' heme is discussed. Rotating disk electrode (RDE) voltammetry has been used to determine a Michaelis constant of 48 mu M and a minimum turnover number of 110 s(-1) for the adsorbed enzyme at 3 degrees C. Adsorbed CCP was found to exhibit the same trend with regard to inhibition by anions as does solution CCP, i.e., CN- > F- > N-3(-) >> Cl-. From these and previous results, we conclude that the catalytic function og CCP remains essentially intact when strongly adsorbed on EPG.