· CO-dehydrogenase catalyzes the oxidation of CO with H2O yielding CO2, 2H+ und 2 e-. Mo- und Ni-containing species are known und show no resemblance in their amino acid sequences or cofactor composition. · Mo-containing CO-dehydrogenase has been grouped in the enzyme family of molybdenum hydroxylases und exhibits in addition to a marked sequence homology, also a common cofactor composition with most of these enzymes. The family of molybdenum hydroxylases comprises eu- und prokaryotic enzymes like xanthine oxidases/dehydrogenases und aldehyde oxidase. · Mo-containing CO-dehydrogenases are known as molybdo-iron-sulfur-flavoproteins · The determined crystal structure of the Mo-containing CO-dehydrogenase is the first structure of a CO-dehydrogenase as well as the first structure of a molybdo-iron-sulfur-flavoprotein. The structure has been determined employing Patterson-search techniques und MAD techniques. The characterization of the atomical/near atomical resolved structures has been enabled through crystal transformation on the free-mounting system for the optimization of diffraction quality. · The crystal structure of the Mo-containing CO-dehydrogenase from Oligotropha carboxidovorans has been determined to a resolution of 1.09 Å for the 277 kDa enzyme und is built up by a dimer of heterotrimers (LMS)2. Each subunit carries one type of cofactor. The L subunit is the molybdoprotein und harbours the active site. The M subunit is the flavoprotein, carrying a non-covalently bound FAD molecule. The S subunit is the iron-sulfur protein und carries two spectroscopically distinguishable [2Fe-2S]-Clusters. · The active site of CO-dehydrogenase consists of a novel Cu(I)- und Mo(+VI/+IV)-containing binuclear cluster, bridged by a m-sulfido ligand. The five ligands around Mo form a distorted tetrahedral geometry with the dithiolene sulfurs straddling over one vertex of the tetrahedron. In addition to the two dithiolene sulfurs, Mo is ligated by one oxo-, one hydroxo- und one sulfido-ligand. Cu(I) is coordinated by two ligands in a distorted linear geometry, the m-sulfido ligand und Sg of Cys 388. The cluster has been discovered by MAD methods und is the first Mo- und Cu-containing cluster found in an enzyme. Its existence contradicts a central dogma of molybdopterin containing enzymes, reflected in their name mononuclear molybdenum enzymes in contrast to the polynuclear Mo-containing nitrogenases (Hille 1996). · Crystallographic studies on the reaction mechanism of CO oxidation comprises the characterization of the oxidized, anoxygenically CO-, H2- und dithionite reduced, CN--inactivated und an n-butylisonitril (nBIC) bound state of the enzyme at resolutions in the atomic/near atomic range. · A reaction mechanism developed on the basis of these results is based on the analogy between the nBIC bound state und a possible intermediate of CO oxidation, as well as on the known chemistry of Cu(I) complexes. Binding und activation of the substrate occurs at the substitution-labile Cu(I) complex, leading to the opening of the cluster. This opening results in the destabilization of oxidized Mo(+VI) with the subsequent reduction of Mo und the formation of a "spectator oxo"-triple bond at Mo. · This reaction mechanism can also explain the activation und oxidation of H2 at the [CuMo] cluster. · Because of the remarkable conservation of the direct Mo environment it appears likely, that the destabilization of oxidized Mo together with the formation of a "spectator oxo" triple bond for the stabilization of the reaction intermediate is also used by other members of the molybdenum hydroxylase family. · In cases of Mo-shortage or -depletion in the growth media Hydrogenophaga pseudoflava synthesizes an inactive CO-dehydrogenase containing cytosin diphosphat instead of the molybdopterin-cytosin dinucleotid cofactor, which has been determined by X-ray crystallography together with the active form. The Mo-containing structures of the two carboxidotrophic bacteria are highly similar.     «

· CO-dehydrogenase catalyzes the oxidation of CO with H2O yielding CO2, 2H+ und 2 e-. Mo- und Ni-containing species are known und show no resemblance in their amino acid sequences or cofactor composition. · Mo-containing CO-dehydrogenase has been grouped in the enzyme family of molybdenum hydroxylases und exhibits in addition to a marked sequence homology, also a common cofactor composition with most of these enzymes. The family of molybdenum hydroxylases comprises eu- und prokaryotic enzymes li...     »