X-ray absorption spectroscopic evidence for a unique nickel site in Clostridium thermoaceticum carbon monoxide dehydrogenase

Journal Article · Wed Jul 29 04:00:00 EDT 1987 · Inorg. Chem.; (United States)

DOI:https://doi.org/10.1021/ic00262a027· OSTI ID:5648526

Cramer, S P; Eidsness, M K; Pan, W H; Morton, T A; Ragsdale, S W; DerVartanian, D V; Ljungdahl, L G; Scott, R A

Carbon monoxide dehydrogenase (COdH) in Clostridium thermoaceticum is an ..cap alpha../sub 3/..beta../sub 3/ protein containing six nickels per molecule, in addition to a number of Fe-S clusters. Previous electron paramagnetic resonance (EPR) spectroscopic work has suggested that nickel is involved in binding CO forming an EPR-detectable species, which is probably a key intermediate in the oxidation of CO to CO/sub 2/ and in the synthesis of acetate. In order to better define the nature of this nickel site, Ni X-ray absorption spectra have been recorded and interpreted by comparison with model compounds. The extended X-ray absorption fine structure (EXAFS) spectrum for oxidized COdH is different from that of other Ni enzymes. Both the EXAFS and the X-ray absorption edge spectra suggest a Ni site containing substantial sulfur ligation. The Ni X-ray absorption edge spectrum of rubredoxin-oxidized COdH exhibits a characteristic shoulder with an inflection point at 8336 eV. Such a feature is absent in octahedral model compounds, whereas a well-resolved peak is observed in square-planar Ni complexes. A distinct 1s ..-->.. 3d transition at 8333 eV is observed in a tetrahedral model. The lack of correspondence suggests that square-pyramidal and distorted-square-planar geometries are plausible candidates for the COdH Ni site. Treatment of rubredoxin-oxidized COdH with hydrogenase and H/sub 2/ shifts the Ni edge to lower energies, indicating Ni-based reduction. 34 references, 3 figures.

• Research Organization: Exxon Research and Engineering Company, Annadale, NJ
• DOE Contract Number: AS09-79ER10499
• OSTI ID: 5648526
• Journal Information: Inorg. Chem.; (United States), Journal Name: Inorg. Chem.; (United States) Vol. 26:15; ISSN INOCA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
BACTERIA
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CHALCOGENIDES
CHEMICAL REACTIONS
CLOSTRIDIUM
COMPLEXES
ENZYMES
MICROORGANISMS
MOLECULAR STRUCTURE
NICKEL COMPLEXES
ORGANIC COMPOUNDS
OXIDATION
OXIDES
OXIDOREDUCTASES
OXYGEN COMPOUNDS
PROTEINS
SPECTROSCOPY
TRANSITION ELEMENT COMPLEXES
X-RAY SPECTROSCOPY