Carbon monoxide dehydrogenase from Methanosarcina frisia Go1 - Characterization of the enzyme and the regulated expression of two operon-like cdh gene clusters

Carbon monoxide dehydrogenase (Cdh) has been anaerobically purified from Methanosarcina frisia Gol. The enzyme is a Ni2+-, Fe2+-, and S2--containing alpha(2) beta(2) heterotetramer of 214 kDa with a pI of 5.2 and subunits of 94 and 19 kDa. It has a V-max of 0.3 mmol of CO min(-1) mg(-1) and K-m values for CO and methyl viologen of approximate to 0.9 mM and 0.12 mM, respectively. EPR spectroscopy on the reduced enzyme showed two overlapping signals: one indicative for 2 (4Fe-4S)(+) clusters and a second signal that is atypical for standard Fe/S clusters. The latter was, together with high spin EPR signals of the oxidized enzyme tentatively assigned to an Fe/S cluster of high nuclearity.