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 (CODHIICh), 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.