Purification of Carbon Monoxide Dehydrogenase, a Nickel Enzyme from Clostridium Thermocaceticum

Carbon monoxide dehydrogenase (CO dehydrogenase) has been purified from the homoacetate-fermenting bacterium, Clostridium thermoaceticum. By use of 63Ni, it has been determined that the dehydrogenase is a metallo nickel enzyme. Nickel was rapidly taken up by the organism and most of the ingested metal was found to be incorporated into CO dehydrogenase. As estimated by gel filtration, the native enzyme has a molecular weight of 410,000. Ferredoxin and a membrane-bound b-type cytochrome, both obtained from C. thermoaceticum, are rapidly reduced by the enzyme in the presence of carbon monoxide and both are considered to be native electron carriers. FMN and Desulfovibrio vulgaris cytochrome c3 were also reduced by the enzyme, while spinach ferredoxin, FAD, NAD, and NADP were not. CO dehydrogenase activity was not appreciably affected by propyl iodide, methyl iodide, carbon tetrachloride, or metal chelators, but was reversibly inhibited by KCN. A method for the in situ assay of CO dehydrogenase in polyacrylamide gels is presented.