Carbon Monoxide Dehydrogenase Reduces Cyanate to Cyanide

The biocatalytic function of carbon monoxide dehydrogenase (CODH) has a high environmental relevance owing to its ability to reduce CO₂ . Despite numerous studies on CODH over the past decades, its catalytic mechanism is not yet fully understood. In the present combined spectroscopic and theoretical study, we report first evidences for a cyanate (NCO^- ) to cyanide (CN^- ) reduction at the C-cluster. The adduct remains bound to the catalytic center to form the so-called CN^- -inhibited state. Notably, this conversion does not occur in crystals of the Carboxydothermus hydrogenoformans CODH enzyme (CODHII_Ch ), as indicated by the lack of the corresponding CN^- stretching mode. The transformation of NCO^- , which also acts as an inhibitor of the two-electron-reduced C_red2 state of CODH, could thus mimic CO₂ turnover and open new perspectives for elucidation of the detailed catalytic mechanism of CODH.