Rapid and Efficient Electrocatalytic CO_2/CO Interconversions by Carboxydothermus hydrogenoformans CO Dehydrogenase I on an Electrode

摘要

Microbial interconversions between CO and CO_2 are catalyzed by carbon monoxide dehydrogenases (CODH). These enzymes fall into three classes: Mo-CODH in which the active site is a CuMo-pterin, Ni-CODH in which the active site is a [Ni4Fe-5S] cluster, and Ni-CODH/ACS, in which a Ni-CODH is part of a larger complex coupling CO_2 reduction to acetyl CoA synthesis. The Ni-CODHs function in both directions, which is significant as both CO_2 and CO can be primary carbon sources and CO is an electron source. As evident from the standard reduction potential for reaction 1A (E~θ = —0.10 V vs SHE at pH 0; corresponding to approximately —0.51 V at pH 7), CO is more reducing than H_2, and this property is the basis for the industrial "water gas shift reaction" (1B) in which H_2 is produced from water. Both CO and CO_2 are unreactive without a catalyst, but enzyme-catalyzed reactions are fast, with turnover frequencies as high as 40000 s~(-1) reported for CO oxidation by a Ni-CODH at pH 8, 70 ℃~3.