Simple formal kinetics for the reversible uptake of molecular hydrogen by [Ni-Fe] hydrogenase from Desulfovibrio gigas

Enzymatic electrocatalysis, triggered and monitored by means of cyclic voltammetry, enabled us to achieve quantitative analysis of the kinetics of the hydrogenase catalyzed process, in the 7.8-10.0 pH range, in the presence of an electrochemically generated redox mediator. The quantitative analysis can be carried out by use of a quite simple SRC model. The simplicity of the SRC model is compatible with the existence of multiple redox microstates, which can be combined in a potential adjustable triangular mechanism consisting of three catalytic cycles, which are formally identical from the kinetic point of view. The steps involved in the kinetic control of the reversible process are H-2 uptake or production at the Ni-Fe catalytic site and the intermolecular electron transfer between the mediator and the distal [4Fe-4S] cluster. The related rate constants have been determined. For the two accompanying intramolecular electron transfers which proceed at equilibrium, the equilibrium constants were found to be in very good agreement with previously published data.