Comparison of rotating disk and wall-jet electrode systems for studying the kinetics of direct and mediated electron transfer for horseradish peroxidase on a graphite electrode

This paper presents a comparison between the results obtained for the kinetics of direct and mediated electroreduction of hydrogen peroxide at horseradish peroxidase (HRP) modified graphite electrodes, used either as a rotating disk electrode (RDE) or as the working electrode in a wall-jet flow through cell. The advantages of using a wall-jet flow system compared with a RDE system for kinetic investigations are that there is no need to account for substrate consumption, especially in the case of desorption of enzyme, and also when studying product-inhibited enzymes. The comparison reveals that identical results can be obtained using either technique. The ratio of HRP molecules on the graphite surface in direct electron transfer contact was determined as 48 +/- 4%, and the turnover number of the heterogeneous electron transfer between adsorbed HRP and the graphite electrode was determined as 1.9 +/- 0.3 s(-1). (C) 1998 Elsevier Science S.A. All rights reserved.