| Abstract
| - Carbon monoxide dehydrogenase/acetyl-CoA synthase (CODH/ACS) is a bifunctional enzymethat catalyzes the reversible reduction of carbon dioxide into carbon monoxide and the coupled synthesisof acetyl-CoA from the carbon monoxide produced. Exposure of CODH/ACS from Moorella thermoaceticato carbon monoxide gives rise to several infrared bands in the 2100−1900 cm-1 spectral region that areattributed to the formation of metal-coordinated carbon monoxide species. Infrared bands attributable toM−CO are not detected in the as-isolated enzyme, suggesting that the enzyme does not contain intrinsicmetal-coordinated CO ligands. A band detected at 1996 cm-1 in the CO-flushed enzyme is assigned asarising from CO binding to a metal center in cluster A of the ACS subunit. The frequency of this bandis most consistent with it arising from a terminally coordinated Ni(I) carbonyl. Multiple infrared bands at2078, 2044, 1970, 1959, and 1901 cm-1 are attributed to CO binding at cluster C of the CODH subunit.All infrared bands attributed to metal carbonyls decay in a time-dependent fashion as CO2 appears in thesolution. These observations are consistent with the enzyme-catalyzed oxidation of carbon monoxide untilit is completely depleted from solution during the course of the experiments.
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