On the Kinetics of CO₂ Reduction by Ni, Fe-CO Dehydrogenases

Abstract

Ni,Fe-CO dehydrogenases (CODHases) catalyze reversibly the reduction of CO2 to CO, making them valuable catalysts for the generation of renewable fuels. The individual states of the active site cluster C during catalysis have been extensively studied by spectroscopic and crystallographic methods but less so by enzyme kinetics. Here, we report the kinetic characterization of three CODHases with distinct physiological roles with two reductants and at different temperatures. For all CODHases, a two-site ping-pong model fits to the data for both reductants. However, we cannot eliminate the possibility of alternative models by using the data. Our kinetic characterization provided insights into the rate-determining steps in catalysis and allowed modeling the influence of the reduction potential of the electron-transferring clusters on catalysis. Furthermore, we investigated potential clues for the different activities of the CODHases and found a point mutation that doubled the activity of the CODH-III/acetyl-CoA synthase complex. However, the main reason for the different activities seems to be the architecture of the substrate tunnels. These findings open up fresh perspectives for understanding and engineering efficient CO2 reduction catalysts.