OUP accepted manuscript

While formate dehydrogenases (FDHs) have been used for cofactor recycling in chemoenzymatic synthesis, the ability of FDH to reduce CO 2 could also be utilized in the conversion of CO 2 to useful products via formate (HCOO -).In this study, we investigated the reduction of CO 2 in the form of hydrogen carbonate (HCO 3 -) to formate by FDHs from Candida methylica (CmFDH) and Chaetomium thermophilum (CtFDH) in a NADH-dependent reaction.The catalytic performance with HCO 3 -as a substrate was evaluated by measuring the kinetic rates and conducting productivity assays.CtFDH showed a higher efficiency in converting HCO 3 -to formate than CmFDH, whereas CmFDH was better in the oxidation of formate.The pH optimum of the reduction was at pH 7-8.However, the high concentrations of HCO 3 -reduced the reaction rate.CtFDH was modeled in the presence of HCO 3 -showing that it fits to the active site.The active site setting for hydride transfer in CO 2 reduction was modeled.The hydride donated by NADH would form a favorable contact to the carbon atom of HCO 3 -, resulting in a surplus of electrons within the molecule.This would cause the complex formed by hydrogen carbonate and the hydride to break into formate and hydroxide ions.