Activation of CO₂ by Vanadium Nitrogenase

Abstract

The reduction of CO into useful products, including hydrocarbon fuels, is an ongoing area of particular interest due to efforts to mitigate buildup of this greenhouse gas. While the industrial Fischer-Tropsch process can facilitate the hydrogenation of CO with H to form short-chain hydrocarbon products under high temperatures and pressures, a desire to perform these reactions under ambient conditions has inspired the use of biological approaches. Particularly, enzymes offer insight into how to activate and reduce CO , but only one enzyme, nitrogenase, can perform the multielectron, multiproton reduction of CO into hydrocarbons. The vanadium-containing variant, V-nitrogenase, displays especial reactivity towards the hydrogenation of CO and CO . This Focus Review discusses recent progress towards the activation and reduction of CO with three primary V-nitrogenase systems. These systems span both ATP-dependent and ATP-independent processes and utilize approaches with whole cells, isolated proteins, and extracted cofactors.

The Fe Protein: An Unsung Hero of Nitrogenase

“…An additional function that has recently been identified for nitrogenase Fe proteins is not related to nitrogen fixation or cofactor biosynthesis [33]. Rebelein and co-workers discovered that both NifH and its counterpart from V-nitrogenase, VnfH, could support the interconversion between carbon monoxide (CO) and carbon dioxide (CO 2 ) [34].…”

A Comparative Analysis of the CO‐Reducing Activities of MoFe Proteins Containing Mo‐ and V‐Nitrogenase Cofactors

“…Nitrogenase is a complex metalloenzyme that catalyzes the ambient reduction of a wide range of substrates. The best‐known function of nitrogenase is the reduction of nitrogen (N 2 ) to ammonia (NH 3 ) in a process that parallels the industrial Haber–Bosch process, which supplies the essential nitrogen element for the entire food chain . In recent years, nitrogenase has also been shown to reduce small C 1 substrates, such as carbon monoxide, carbon dioxide and cyanide, to hydrocarbons in a process that mirrors the industrial Fischer–Tropsch process, thereby adding another important function to its catalytic repertoire .…”

“…,3 and 4 ,respectively). This observation is consistent with an increased formation of this product by VnfDGKu pon substitution of D 2 Of or H 2 O (Figure 1C, 2 ).…”

“…Notably,i na nalogy to the ability of VnfDGK to generate considerably more C 2 H 4 than NifDK(Figure 2A, 2vs. 1 ), NifDK V generates % 12 %m ore C 2 H 4 than NifDK M from CO reduction( Figure2A, 4 vs 3. ).…”

“…The bestknown function of nitrogenase is the reduction of nitrogen (N 2 )t oa mmonia (NH 3 )i naprocess that parallels the industrial Haber-Bosch process, whichs upplies the essential nitrogen element for the entire food chain. [1][2][3] In recent years, nitrogenase has also been shown to reduce small C 1 substrates, such as carbon monoxide, carbon dioxide and cyanide,t oh ydrocarbons in ap rocess that mirrorst he industrial Fischer-Tropsch process,t hereby adding another important function to itscatalytic repertoire. [4][5][6][7] The activities of nitrogenase in these reactions are enabledb yat wo-component system;i nt he cases of the homologous molybdenuma nd vanadium nitrogenases, ar eductase component (collectively termedt he Fe protein) is used to donate electrons in an ATP-dependent mannert o the cofactor of the catalytic component (designated the MoFe and VFe protein, respectively), where substrate reduction occurs.…”