ELECTROCATALYTIC REDUCTION OF HYDROGEN-PEROXIDE AT A STATIONARY PYROLYTIC-GRAPHITE ELECTRODE SURFACE IN THE PRESENCE OF CYTOCHROME-C PEROXIDASE - A DESCRIPTION BASED ON A MICROELECTRODE ARRAY MODEL FOR ADSORBED ENZYME MOLECULES

Electrochemical reduction of H2O2 at pyrolytic graphite disc electrode s of radius 2.5 mm occurs at readily accessible potentials (600 mV ver sus the standard hydrogen electrode) in the presence of yeast cytochro me c peroxidase. Introduction of the enzyme into the electrolyte solut ion initiates large changes in the ellipsometric angles measured for t he electrode-solution interface, consistent with time-dependent enzyme adsorption. This process may be correlated with changes in electroche mical activity. Over the same time course, linear-sweep voltammograms are characterized by a transition from a sigmoidal to a peak-type wave form. It is proposed that the time-dependent behaviour may be rational ized by use of a microscopic model for substrate mass transport, in wh ich the two-electron reduction of peroxide occurs at electrocatalytic sites consisting of adsorbed enzyme molecules. A voltammetric theory b ased on treating the adsorbed redox enzymes as an expanding array of m icroelectrodes is in excellent agreement with experiment.