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On the Steady-State Assumption and Its Application to the Rotating Disk Voltammetry of Adsorbed Enzymes

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journal contribution
posted on 31.03.2005, 00:00 by Michael J. Honeychurch, Paul V. Bernhardt
Rotating disk voltammetry is routinely used to study electrochemically driven enzyme catalysis because of the assumption that the method produces a steady-state system. This assumption is based on the sigmoidal shape of the voltammograms. We have introduced an electrochemical adaptation of the King−Altman method to simulate voltammograms in which the enzyme catalysis, within an immobilized enzyme layer, is steady-state. This method is readily adaptable to any mechanism and provides a readily programmable means of obtaining closed form analytical equations for a steady-state system. The steady-state simulations are compared to fully implicit finite difference (FIFD) simulations carried out without any steady-state assumptions. On the basis of our simulations, we conclude that, under typical experimental conditions, steady-state enzyme catalysis is unlikely to occur within electrode-immobilized enzyme layers and that typically sigmoidal rotating disk voltammograms merely reflect a mass transfer steady state as opposed to a true steady state of enzyme intermediates at each potential.