Interpreting the Catalytic Voltammetry of Electroactive Enzymes Adsorbed on Electrodes

Steady-state electrocatalytic waveforms displayed by redox enzymes adsorbed on electrodes are analyzed to reveal and quantify important mechanistic characteristics of the active sites involved in catalysis and to elucidate the contributions of different factors in determining the overall electron-transport rates. The shape, height, steepness, and potential of the voltammetric waves are functions of mass transport, interfacial electron-transfer rates, and the intrinsic kinetic and thermodynamic properties of the enzyme. A model is constructed first for the most simple realistic case, an enzyme containing a single two-electron active site, and then this is extended to include additional electron-transfer centers that serve as intramolecular relays. Equations are derived that predict the steady-state behavior expected for different conditions, and the models are used to assess recent experimental results. An alternative perspective on enzyme catalytic electron-transport is thus presented, in which kinetics and energetics are viewed and analyzed in the potential domain.