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The CODH activity occurs at the C cluster. This cluster looks much like the A cluster (Ni-X-Fe4S4) except the environment of the cluster is different enough to change the catalytic properties. This cluster is where the carbon dioxide is reduced to carbon monoxide: CO2 + 2H+ + 2e- <-> CO + H2O Once the CO2 binds, there is a subtle change in the shape of the enzyme that prohibits the CO, when released from the active site, from escaping into the cytoplasm. Being cut off, there is only one escape: move through the molecular tunnel in the enzyme to the A cluster situated by the exit. One electron comes from the reduced B cluster, and one electron cones from the reduce C cluster itself. This is a reversible reaction; it's conceivable that the toxic effects of CO can be somewhat neutralized by the cell by turning it into CO2. However, since CO is not common in the environment it is doubtful that the bacterium uses the reversed reaction to save itself.
By the way, the name carbon monoxide dehydrogenase comes from the class of enzymes to which this activity belongs. You'll notice there is no hydrogen on CO2 to dehydrogenate, but if you reverse the reaction above, you can see what is dehydrogenated. Next: My Research |
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