文摘
The structurally characterized molybdoenzyme carbon monoxide dehydrogenase (CODH)catalyzes the oxidation of CO to CO2 in the aerobic bacterium Oligotropha carboxidovorans. The activesite of the enzyme was studied by Mo- and Cu-K-edge X-ray absorption spectroscopy. This revealeda bimetallic [CuISMoVI(=O)2] cluster in oxidized CODH which was converted into a [CuISMoIV(=O)OH(2)] cluster upon reduction. The Cu···Mo distance is 3.70 Å in the oxidized form and is increased to4.23 Å upon reduction. The bacteria contain CODH species with the complete and functional bimetalliccluster along with enzyme species deficient in Cu and/or bridging S. The latter are precursors in theposttranslational biosynthesis of the metal cluster. Cu-deficient CODH is the most prominent precursorand contains a [HSMo(=O)OH(2)] cluster. Se-K-edge X-ray absorption spectroscopy demonstrates thatSe is coordinated by two C atoms at 1.94-1.95 Å distance. This is interpreted as a replacement of the Sin methionine residues. In contrast to a previous report [Dobbek, H., Gremer, L., Meyer, O., and Huber,R. (1999) Proc. Natl. Acad. Sci. U.S.A. 96, 8884-8889] Se was not identified in the active site of CODH.