Electrocatalytic Aldehyde Oxidation by a Tungsten Dependent Aldehyde Oxidoreductase from Aromatoleum Aromaticum

Abstract

In contrast to their molybdenum dependent relatives, tungsten enzymes operate at significantly lower redox potentials, and in some cases they can carry out reversible redox transformations of their substrates and products. Still, the electrochemical properties of W enzymes have received much less attention than their Mo relatives. Herein we analyse the tungsten enzyme aldehyde oxidoreductase (AOR) from the mesophilic bacterium Aromatoleum aromaticum which has been immobilised on a glassy carbon working electrode. This generates a functional system that electrochemically oxidises a wide variety of aromatic and aliphatic aldehydes in the presence of the electron transfer mediators benzyl viologen, methylene blue or dichlorophenol indophenol. Simulation of the cyclic voltammetry has enabled a thorough kinetic analysis of the system, which reveals that methylene blue acts as a two‐electron acceptor. In contrast, the other two mediators act as single electron oxidants. The different electrochemical driving forces imparted by these mediators also lead to significantly different outer sphere electron transfer rates with AOR. This work shows that electrocatalytic aldehyde oxidation can be achieved at a low applied electrochemical potential leading to an extremely energy efficient catalytic process.

The Reversible Electrochemical Interconversion of Formate and CO2 by Formate Dehydrogenase from Cupriavidus necator

“…A similar observation was reported for other enzymes in the literature. , However, the catalytic activity was notably improved by adding chitosan to the GTA-FdsDABG mixture, leading to a very stable and highly active film comprising a mixture of 2 μL of chitosan (0.25%), 2 μL of GTA (0.25%), and 3 μL of FdsDABG (86 μM). A similar strategy was used recently by our group to immobilize W-containing aldehyde oxidoreductase, and the resulting enzyme film exhibited excellent electrocatalytic activity along with stability . The as-prepared electrode is abbreviated as GC/Chit+FdsDABG+GTA hereafter.…”

“…A similar strategy was used recently by our group to immobilize W-containing aldehyde oxidoreductase, and the resulting enzyme film exhibited excellent electrocatalytic activity along with stability. 38 The as-prepared electrode is abbreviated as GC/Chit+FdsDABG +GTA hereafter. The resulting modified electrode was stored at 4 °C in phosphate buffer solution (pH 7.2) when not in use.…”

A bacterial tungsten-containing aldehyde oxidoreductase forms an enzymatic decorated protein nanowire

“…The unprecedented ability of this enzyme to use hydrogen as an electron donor for acid or NAD + reduction qualifies the enzyme as a new type of hydrogenase ( 18 ). In addition, the enzyme can also be coupled to an electrochemical cell ( 19 ). AOR Aa is insensitive to oxygen in cell extracts, stable in isolated form and active at room temperature.…”

A pH-dependent shift of redox cofactor specificity in a benzyl alcohol dehydrogenase of aromatoleum aromaticum EbN1

“…Another convenient source of the electrons needed for acid reduction and NADH recycling by AOR would be an electrochemical cell. This principle has already been proven by showing electrochemical coupling of reactions catalysed by AOR (Kalimuthu et al 2023 ) and by setting up an ATP-producing enzyme cascade reaction with AOR (Luo et al 2023 ). Although the product concentrations produced in these assays are expected to stay relatively low even after further optimisation of the biological processes, some promising processes to concentrate alcohols from aqueous solutions with reasonably low energy demand are being developed, such as pervaporation (Golubev et al 2018 ), membrane destillation (Alkhudhiri et al 2012 ) or vapor-phase membrane filtration (Shalygin et al 2023 ).…”