The Catalytic Bias of 2-Oxoacid:ferredoxin Oxidoreductase in CO₂: evolution and reduction through a ferredoxin-mediated electrocatalytic assay

Enzymes from the 2-oxoacid: ferredoxin oxidoreductase (OFOR) family engage in both CO₂ evolution and reduction in nature, depending on their physiological roles. Two enzymes and their redox partner ferredoxins (Fds) from Hydrogenobacter thermophilus and Desulfovibrio africanus were examined to investigate the basis of the catalytic bias. The Fd1 from H. thermophilus demonstrated a potential of ∼ −485 mV at room temperature, the lowest for known single [4Fe-4S] cluster Fds. It suggests a low potential electron donor may be the key factor in overcoming the large thermodynamic barrier of CO₂ reduction. The Fd-mediated electrocatalytic experiments further demonstrated the impact of Fd's potential on the direction of the OFOR reaction: as OFOR enzymes could essentially catalyze both CO₂ evolution and reduction in vitro, the difference in their physiological roles is associated with the reduction potential of the redox partner Fd. The electrocatalytic assay could study both CO₂ evolution and reduction in one setup and is a good tool to probe Fds' reactivity that arise from their reduction potentials.