O2 Inhibition of Ni-Containing CO Dehydrogenase Is Partly Reversible

Ni-containing CO dehydrogenases (CODHs) are very efficient metalloenzymes that catalyze the conversion between CO2 and CO. They are a source of inspiration for designing CO2-reduction catalysts and can also find direct use in biotechnology. They are deemed extremely sensitive to O-2, but very little is known about this aspect of their reactivity. We investigated the reaction with O-2 of Carboxydothermus hydrogenoformans (Ch) CODH II and the homologous, recently characterized CODH from Desulfovibrio vulgaris (Dv) through protein film voltammetry and solution assays (in the oxidative direction). We found that O-2 reacts very quickly with the active site of CODHs, generating species that reactivate upon reduction-this was unexpected. We observed that distinct CODHs exhibit different behaviors: Dv CODH reacts half as fast with O-2 than Ch CODH, and only the former fully recovers the activity upon reduction. The results raise hope that fast CO/CO2 biological conversion may be feasible under aerobic conditions.