Mediated Electron Transfer at Redox Active Monolayers. Part 4: Kinetics of Redox Enzymes Coupled With Electron Mediators

Abstract

Abstract:A detailed kinetic analysis of the pertinent physical processes underlying the operation of enzyme electrodes immobilized within alkane thiol self assembled monolayers is developed. These electrodes utilize a soluble mediator, which partitions into the monolayer, regenerates the active catalytic form of the enzyme and is re-oxidized at the underlying support electrode surface giving rise to a current which reflects kinetic events at the enzyme surface. Both the enzyme/substrate and enzyme mediator kinetics have been quantified fully in terms of a ping-pong mechanism for the former and Michaelis-Menten kinetics for the latter. The effect of substrate and mediator diffusion in solution have also been specifically considered and the latter processes have been shown to result in a complex expression for the reaction flux. Four limiting kinetic cases have been enumerated and simple expressions for the reaction flux in each of these rate limiting situations have been developed. Kinetic case diagrams have been presented as an aid to mechanistic diagnosis. The complicating effects of diffusive loss of reduced mediator from the enzyme layer have also been examined and the relation between the observed flux corresponding to reduced mediator oxidation at the support electrode and the substrate reaction flux in the enzyme layer have been quantified in terms of an efficiency factor. Results extracted from recently published practical realizations of immobilized monolayer enzyme systems have been discussed in the context of the proposed model analysis.

Reciprocal Sum Expression for Steady-state Kinetics —Enzyme Reactions and Voltammetry—

“…3 However, it is not a right term in mathematical sense, but it should be called reciprocal sum, as described here. In the following, we will Electrochemistry, 90 (10), 103002 (2022) apply the reciprocal sum concept to some typical examples of enzyme kinetics and steady-state voltammetry.…”

“…The steady-state kinetic equations derived here are the typical ones in the biochemistry fields. For other complicated cases also, we Electrochemistry, 90 (10), 103002 (2022) can easily derive kinetic equations by defining the limiting rate equations for the individual rdss. One may add other rdss by considering additional intermediate in the modeling, but the corresponding equations will be simplified to those described here.…”

“…When the electrode system is totally irreversible, the re-reduction Electrochemistry, 90 (10), 103002 (2022) of the electrochemically generated O is ignored, and Eq. 69 is simplified as (see also Eq.…”

“…CO,s . Therefore, the electrocatalysis-controlled hypothetical limiting current involving a bi-directional electrode reaction is given by: Electrochemistry, 90 (10), 103002 (2022)…”

Multi-faceted strategy based on enzyme immobilization with reactant adsorption and membrane technology for biocatalytic removal of pollutants: A critical review

“…It should be mentioned that the addition of mediator agents also alters the enzymatic kinetics. However, the Michaelis-Menten kinetic model could be used to estimate the affinity of the oxidoreductases towards different mediators and reaction substrates after the addition of the mediators, and to evaluate the changes in the enzyme kinetics (Lyons, 2003). The most frequently used mediator agents include e.g.…”