Carbon monoxide dehydrogenase function

Figure 2 Structures of the actrive sites of metalloenzymes containing metal-sulfur cluster units, (a) Fe only hydrogenase, H-cluster (Hoxfarm) (b) Sulfite reductase (c) NiFe carbon monoxide dehydrogenase, C-cluster and (d) NiFe carbon monoxide dehydrogenase, A-cluster, which functions as acetyl-CoA synthase...

Concerning the general topic of ferredoxin and redox proteins, it is important to note the existence of several of these in various methanogens. Ferredoxin has been reported in M barkeri [iQ2], M. thermophila [249,303], and Methanococcus thermolithotrophicus [304,305]. In one case, ferredoxin is required in electron transfer from carbon monoxide dehydrogenase to a membrane-bound hydrogenase in M. thermophila [306]. Another redox protein, referred to as a glutaredoxin-like protein , has been isolated from M. thermoautotrophicum [307], but has no known function. As mentioned above, MVH gene clusters contain a sequence for a polyferredoxin of unknown function. 

Fig. 11. Proposed function of electrochemical and Na potentials in energy conservation coupled to acetate fermentation to CH4 and CO2. The Na /H antiporter is involved in the generation of A/iH from A/iNa. CH3CO-S-C0A, acetyl-coenzyme A [CO], CO bound to carbon monoxide dehydrogenase CH3-H4MPT, methyl-tetrahydromethanopterin CH3-S-C0M, methyl-coenzyme M. The hatched boxes indicate membrane-bound electron transport chains or membrane-bound methyl-transferase catalyzing either IT or Na translocation (see Figs. 5, 6 and 12). It is assumed that enzyme-bound [CO] is energetically equal to free CO. ATP is synthesized via membrane-bound H -translocating ATP synthase. The stoichiometries of translocation were taken from refs. [107,234] n, X, y and z are unknown stoichiometric factors.

Jeon WB, Cheng JJ and Ludden PW (2001) Purification and characterization of membrane-associated CooC protein and its functional role in the insertion of nickel into carbon monoxide dehydrogenase from Rhodospirillum rubrum. J Biol Chem 276 38602-38609. 

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