Voltammetric studies of the catalytic electron‐transfer process between the Desulfovibrio gigas hydrogenase and small proteins isolated from the same genus

Abstract

The kinetics of electron transfer between the Desulfovibrio gigas hydrogenase and several electron-transfer proteins from Desulfovibrio species were investigated by cyclic voltammetry, squarewave voltammetry and chronoamperometry. The cytochrome c3 from Desulfovibrio vulgaris (Hildenborough), Desulfovibrio desulfuricans (Norway 4), Desu@vibrio desulfuricans (American Type Culture Collection 27774) and D. gigas (NCIB 9332) were used as redox carriers. They differ in their redox potentials and isoelectric point. Depending on the pH, all the reduced forms of these cytochromes were effective in electron exchange with hydrogenase. Other small electron-transfer proteins such as ferredoxin I, ferredoxin I1 and rubredoxin from D. gigas were tentatively used as redox carriers. Only ferredoxin I1 was effective in mediating electron exchange between hydrogenase and the working electrode. The second-order rate constants k for the reaction between reduced proteins and hydrogenase were calculated based on the theory of the simplest electrocatalytic mecha- Hydrogenase catalyzes the simple and reversible reaction H, * 2H' + 2e in the presence of suitable electron donors/ acceptors. This enzyme, present in sulfate-reducing bacteria, plays a central role in hydrogen metabolism [l]. A number of hydrogenases have been obtained from various sources, exhibiting different properties with respect to specific activity, oxygen stability, activation behavior, metal content, subunit structure and electron-carrier specificity [ 1 -51.The hydrogenase from the sulfate-reducing anaerobic bacterium Desulfovibrio gigas (molecular mass of 89 kDa with subunits of 26 kDa and 63 kDa [6, 71) contains four redox centers; one nickel center, one [3Fe-4S] and two [4Fe-4S] clusters, whose existence was proven by electron paramagnetic resonance and Mossbauer spectroscopic studies [7,

A variety of hydrogenotrophic enrichment cultures catalyse cathodic reactions

“…It has been previously shown that Desulfovibrio sp. contains enzymes that can directly transfer electron from a cathode 59,60 . It is possible that free enzymes in the liquid could be the reason of observing significant redox curves in the SR MEC .…”

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

“…In the present study, enzymatic electrocatalysis gives access to a kinetic approach of the hydrogenase mechanism. Initially developed with oxidases [20,21], enzymatic electrocatalysis makes use of the coupling between the enzymatically catalyzed oxidation (or reduction) of a redox mediator and the electrochemical detection and regeneration of this mediator [20–27]. In the particular case of hydrogenase kinetics, it has already been pointed out that electrochemical methods are quite suitable because the outstanding reversibility of hydrogenase catalysis can be experimentally controlled and monitored [24,28–30].…”

Hydrogenases from the hyperthermophilic bacterium Aquifex aeolicus: electrocatalysis of the hydrogen production/consumption reactions at carbon electrodes

“…Because of the possible double role of hydrogenases (i.e., H 2 production/consumption), varying the applied potential in the forward/backward direction is a convenient way to investigate electron exchange between hydrogenase and an electrode. The electrochemical approach has been exploited so far to study hydrogenases in the presence of physiological partners such as c-type cytochromes [17][18][19][20][21][22] or of polycationic species facilitating the electron transfers (promoting effect) [23,24]. Evidence of direct H 2 evolution at an electrode acting as an electron donor has also been demonstrated in the absence of a promoting agent [25][26][27].…”