Electron transfer between the hydrogenase from Desulfovibrio vulgaris (Hildenborough) and viologens

Abstract

The electron transfer kinetics between the hydrogenase from Desulvovibrio vulgaris (strain Hildenborough) and three different viologen mediators has been investigated by cyclic voltammetry. The mediators methyl viologen, di(n-aminopropyl) viologen and propyl viologen sulfonate differ in redox potential and in net charge. Dependent on the pH both the one-and two-electron-reduced forms or only the two-electron-reduced form of the viologens are effective in electron exchange with hydrogenase. Calculations of the second-order rate constant k for the reaction between reduced viologen and hydrogenase are based on the theory of the simplest electrocatalytic mechanism. Values for k are in the range of 106-107 M-' s-' and increase in the direction propyl viologen sulfonate + methyl viologen + di(n-aminopropyl) viologen. An explanation is based on electrostatic interactions. It is proposed that the electron transfer reaction is the rate-determining step in the catalytic mechanism.In recent years the study of electron-transfer processes in biological systems by means of electrochemical methods has received increasing attention. For a number of small-sized redox proteins (e. g. cytochrome c, ferredoxines, and azurine) a direct electron transfer at metal oxide electrodes [l] or at gold electrodes modified with organic non-electroactive organic 'promotors' [2] has been achieved. The electrode kinetics of these systems can be investigated by standard techniques like cyclic voltammetry, rotating-disk electrode or impedance measurements. Still, for most (larger-sized) redox enzymes no direct electron transfer at electrodes has been described yet. The literature on the direct electron transfer between redox enzymes and electrodes is still scarce. Some examples are hydrogenase at the dropping mercury electrode in the presence of polylysine [3], covalently modified glucose oxidase at metal Correspandence to J. C. Hoogvliet,

Copper‐containing nitrite reductase from Pseudomonas chlororaphis DSM 50135

“…The theory describing this kind of mechanism has been developed by Nicholson and Shain [24] and by Savéant and Vianello [32] and is frequently applied to kinetic studies of reactions between redox enzymes and mediators. Second order rate constants ( k ) were calculated as described in [25]: the kinetic parameter λ was calculated from the catalytic efficiencies (the ratio of cathodic current in the presence and absence of substrate) using the values computed by Nicholson and Shain, and plotted vs. the inverse of the scan rate. The plots yielded straight lines, confirming the applicability of the Nicholson and Shain theory to the present system, and the variation of the pseudo‐first order rate constant with CuNir concentrations (between 1 and 4 µ m ) yielded a value of k = (2.9 ± 0.9) × 10 4 m −1 ·s −1 for the rate constant between reduced azurin and nitrite reductase.…”

“…The electrochemical response of the azurin was measured in the absence and presence of nitrite reductase. Data were analyzed according to Nicholson & Shain[24], as described by Hoogvliet et al[25].…”

Hydrogenase Activity Control at Desulfovibrio vulgaris Cell-Coated Carbon Electrodes: Biochemical and Chemical Factors Influencing the Mediated Bioelectrocatalysis

“…It is well known [9,15] that pure isolated hydrogenase is able to catalyze both the reduction of protons to hydrogen and the oxidation of hydrogen to protons in the presence of a suitable redox mediator as methyl viologen. Cyclic voltammetry is a convenient way to get information about the kinetics and energetics of turnover and to monitor the efficiency of the catalytic process.…”

“…Cyclic voltammetry is a convenient way to get information about the kinetics and energetics of turnover and to monitor the efficiency of the catalytic process. Thus, addition of hydrogenase to a solution of MV 2 , which behaves as a reversible electrochemical system at a GC electrode, resulted in enhanced cathodic or anodic voltammetric currents [9].…”

Enzyme Electrochemistry — Biocatalysis on an Electrode

“…[263] Mediated hydrogenase electrochemistry has been achieved with electroreduced methyl viologen. [61,264,265] The Armstrong group has reported several papers on the direct electrochemistry of NiFe hydrogenases from Chromatium vinosum, [266] Allochromatium vinosum, [267][268][269][270][271] and Desulfovibrio fructosovorans. [272] These enzymes, in addition to the NiFe cofactor, bear one [3Fe-4S] cluster and two lower potential [4Fe-4S] clusters.…”