International audienceNi-containing Carbon Monoxide Dehydrogenases (CODHs) catalyze the reversible conversion between CO and CO2 and are involved in energy conservation and carbon fixation. These homodimeric enzymes house two NiFeS active sites (C-clusters) and three accessory [4Fe–4S] clusters. The Desulfovibrio vulgaris (Dv) genome contains a two-gene CODH operon coding for a CODH (cooS) and a maturation protein (cooC) involved in nickel insertion in the active site. According to the literature, the question of the precise function of CooC as a chaperone folding the C-cluster in a form which accommodates free nickel or as a mere nickel donor is not resolved. Here, we report the biochemical and spectroscopic characterization of two recombi...