Electrochemical reactions of glucose oxidase at graphite electrodes

Abstract

Differential pulse voltammetry has been used to show that a number of direct electron transfer reactions can occur between glucose oxidase and graphite electrodes. Two of these reactions are due to strongly adsorbed species, indicating that some of the enzymes have undergone extensive and slow unfolding during the interaction with the electrode, leading to the adsorption of the FAD directly onto the graphite surface. The electron transfer reactions due to these strongly adsorbed molecules were not affected by the addition of the enzyme substrate. In contrast, reduction peaks can be observed that are due to molecules either from the solution or from weakly adsorbed molecules. At low concentrations of enzyme in solution (<20 μ M), electron transfer processes can be seen for glucose oxidase molecules that appear not to have undergone extensive conformational changes. Glucose had a marked effect on these electron transfer processes and direct electron exchange between glucose oxidase and graphite resulting from the enzyme catalyzed oxidation of glucose was observed using glucose concentrations up to 1 m M.