title: Electron paramagnetic resonance studies of the tungsten-containing formate dehydrogenase from Clostridium thermoaceticum.
abstract: The redox centers in the tungsten-containing formate dehydrogenase from Clostridium thermoaceticum were examined by potentiometric titration and electron paramagnetic resonance spectroscopy. At low temperature two overlapping iron-sulfur signals which correlated with enzymatic activity were observed with formal potentials near -400 mV vs. SHE. Based on their temperature dependences, one signal is assigned to a reduced Fe2S2 cluster and one to a reduced Fe4S4 cluster. Quantitation of signal intensity suggests two Fe2S2 and two Fe4S4 clusters per formate dehydrogenase molecule. Another signal (g = 2.101, 1.980, 1.950) present in low concentrations at more negative potentials was observable up to 200 degrees K and is not attributed to any iron-sulfur cluster. The possible origin of this signal is analyzed using ligand field theory, and the redox behavior is considered with respect to possible ligation at the active site.
authors.affiliation: Department of Chemistry, Stanford University, CA 94305.
authors.forename: J C
authors.initials: JC
authors.lastname: Deaton
authors.forename: E I
authors.initials: EI
authors.lastname: Solomon
authors.forename: G D
authors.initials: GD
authors.lastname: Watt
authors.forename: P J
authors.initials: PJ
authors.lastname: Wetherbee
authors.forename: C N
authors.initials: CN
authors.lastname: Durfor
mesh_terms: D000445:Aldehyde Oxidoreductases / Q000032:analysis; D001665:Binding Sites; D003013:Clostridium / Q000201:enzymology*; D004578:Electron Spin Resonance Spectroscopy; D005560:Formate Dehydrogenases / Q000032:analysis; D010084:Oxidation-Reduction; D013696:Temperature; D014414:Tungsten / Q000032:analysis*
chemical_list: D005560:Formate Dehydrogenases; D000445:Aldehyde Oxidoreductases; D014414:Tungsten