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 O2, but very little is known about this aspect of their reactivity. We investigated the reaction with O2 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 O2 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 O2 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.