O 2 Inhibition of Ni‐Containing CO Dehydrogenase Is Partly Reversible

Ni‐containing CO dehydrogenases (CODHs) are very efficient metalloenzymes that catalyze the conversion between CO 2 and CO. They are a source of inspiration for designing CO 2 ‐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/CO 2 biological conversion may be feasible under aerobic conditions.