Isolation of carbon monoxide dehydrogenase from Acetobacterium woodii and comparison of its properties with those of the Clostridium thermoaceticum enzyme

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Abstract
An O2-labile CO dehydrogenase was purified to at least 98% homogeneity from fructose-grown cells of A. woodii. Gel filtration and electrophoresis experiments gave MW of 480,000 and 153,000, respectively, of the active enzyme. The MW for the subunits are 80,000 and 68,000: the subunits occur in equal proportion. The small subunit of the A. woodii enzyme differs in size from that of the C. thermoaceticum enzyme; the large subunits are similar. The specific activity of the A. woodii enzyme, measured at 30.degree. C and pH 7.6, is 500 .mu.mol of CO oxidized min-1 mg-1 with 20 mM methyl viologen as the electron acceptor. Analysis revealed (number per dimer) Fe (9), acid-labile sulfide (12), Ni (1.4) and Mg or Zn (1). Tihs metal content is similar to that of the C. thermoaceticum enzyme. The Ni and the Fe-S clusters are redox-active, as was found for the C. thermoaceticum enzyme. CO can reduce and CO2 can oxidize the Fe-S clusters. The enzyme is inhibited by cyanide, but CO2 in the presence of reduced methyl viologen or CO alone can reverse or prevent this inhibition. Several ferredoxins, flavodoxin and rubredoxin and some artificial electron carriers were tested for their relative rates of reaction with the CO dehydrogenases from A. woodii, C. thermoaceticum and C. formicoaceticum. Rubredoxin was by far the most reactive acceptor and is proposed to be the primary natural electron carrier for the acetogenic CO dehydrogenases.

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