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 kinet ics of direct and mediated electroreduction of hydrogen peroxide at horsera dish peroxidase (HRP) modified graphite electrodes, used either as a rotati ng disk electrode (RDE) or as the working electrode in a wall-jet flow thro ugh cell. The advantages of using a wall-jet flow system compared with a RD E system for kinetic investigations are that there is no need to account fo r substrate consumption, especially in the case of desorption of enzyme, an d 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 elect ron 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.