Reduction of Carbon Dioxide by a Molybdenum-Containing Formate Dehydrogenase: A Kinetic and Mechanistic Study

Abstract

Carbon dioxide accumulation is a major concern for the ecosystems, but its abundance and low cost make it an interesting source for the production of chemical feedstocks and fuels. However, the thermodynamic and kinetic stability of the carbon dioxide molecule makes its activation a challenging task. Studying the chemistry used by nature to functionalize carbon dioxide should be helpful for the development of new efficient (bio)­catalysts for atmospheric carbon dioxide utilization. In this work, the ability of Desulfovibrio desulfuricans formate dehydrogenase (Dd FDH) to reduce carbon dioxide was kinetically and mechanistically characterized. The Dd FDH is suggested to be purified in an inactive form that has to be activated through a reduction-dependent mechanism. A kinetic model of a hysteretic enzyme is proposed to interpret and predict the progress curves of the Dd FDH-catalyzed reactions (initial lag phase and subsequent faster phase). Once activated, Dd FDH is able to efficiently catalyze, not only the formate oxidation (k cat of 543 s–1, K m of 57.1 μM), but also the carbon dioxide reduction (k cat of 46.6 s–1, K m of 15.7 μM), in an overall reaction that is thermodynamically and kinetically reversible. Noteworthy, both Dd FDH-catalyzed formate oxidation and carbon dioxide reduction are completely inactivated by cyanide. Current FDH reaction mechanistic proposals are discussed and a different mechanism is here suggested: formate oxidation and carbon dioxide reduction are proposed to proceed through hydride transfer and the sulfo group of the oxidized and reduced molybdenum center, Mo6+S and Mo4+-SH, are suggested to be the direct hydride acceptor and donor, respectively.

Efficient reduction of CO2 by the molybdenum-containing formate dehydrogenase from Cupriavidus necator (Ralstonia eutropha)

“…To ensure compliance with the first law of thermodynamics, the following Haldane relationship relating the steady-state parameters for an enzyme operating via a ping-pong mechanism holds (13). Moura and co-workers (14) have recently examined the reaction of the periplasmic formate dehydrogenase from Desulfovibrio desulfuricans and have concluded that this reaction also proceeds via a hydride transfer mechanism. Like the C. necator enzyme studied here, the D. desulfuricans enzyme possesses a terminal Mo(VI)ϭS sulfido group in the oxidized state but has a selenocysteine ligand to the molybdenum in place of the cysteine residue seen in FdsABG.…”

Molybdenum-Dependent Formate Dehydrogenase for Formate Bioelectrocatalysis in a Formate/O2Enzymatic Fuel Cell

“…Several different mechanisms for FDH-catalyzed formate oxidation have been proposed. 5,9,14,19,20 It was shown by Maia et al that FDH requires an activation step by its reduction using viologen or an artificial reducer.…”

“…7,8 Metal-dependent enzymes can be subdivided into two groups as either molybdenum (Mo)-or tungsten (W)-containing FDHs. 9 The majority of prokaryotic FDHs contains Mo as the active site metallo-component in the place of W, which is mainly found in FDHs obtained from organisms living in extreme conditions (i.e., strict anaerobes). 10 Methylobacterium extorquens AM, a methylotrophic bacteria, can produce NAD-dependent FDH under aerobic conditions.…”

“…5,9,14,19,20 It was shown by Maia et al that FDH requires an activation step by its reduction using viologen or an artificial reducer. 9 Robinson et al have proposed a reductive activation to create a stabilized form of the SeCys dissociated state and it was mentioned that this state is also possible upon incubation of the protein with reducing agents (such as sodium dithionite (DT)). 15,19 Thus, we evaluated the activation of FDH using 2-mercaptoethanol (2-ME) as a reducing agent.…”

Environmental Catalysis: Present and Future

“…Using a bio-synthetic approach, synthetic inorganic chemists have developed synthetic models to mimic a number of metalloenzymes such as hydrogenases, nitric oxide reductase, cytochrome, among others. [133][134][135] Despite the catalytic efficiencies obtained for this artificial systems are low compared with the natural systems, these strategies have gained effectiveness in recent years. Such innovative approach has been successfully used to synthesized artificial electrocatalytic enzymes in a sustainable manner.…”