title: Electrochemical investigations of the interconversions between catalytic and inhibited states of the [FeFe]-hydrogenase from Desulfovibrio desulfuricans.
abstract: Studies of the catalytic properties of the [FeFe]-hydrogenase from Desulfovibrio desulfuricans by protein film voltammetry, under a H2 atmosphere, reveal and establish a variety of interesting properties not observed or measured quantitatively with other techniques. The catalytic bias (inherent ability to oxidize hydrogen vs reduce protons) is quantified over a wide pH range: the enzyme is proficient at both H2 oxidation (from pH > 6) and H2 production (pH < 6). Hydrogen production is inhibited by H2, but the effect is much smaller than observed for [NiFe]-hydrogenases from Allochromatium vinosum or Desulfovibrio fructosovorans. Under anaerobic conditions and positive potentials, the [FeFe]-hydrogenase is oxidized to an inactive form, inert toward reaction with CO and O2, that rapidly reactivates upon one-electron reduction under 1 bar of H2. The potential dependence of this interconversion shows that the oxidized inactive form exists in two pH-interconvertible states with pK(ox) = 5.9. Studies of the CO-inhibited enzyme under H2 reveals a strong enhancement of the rate of activation by white light at -109 mV (monitoring H2 oxidation) that is absent at low potential (-540 mV, monitoring H+ reduction), thus demonstrating photolability that is dependent upon the oxidation state.
authors.affiliation: Inorganic Chemistry Laboratory, Department of Chemistry, Oxford University, South Parks Road, Oxford OX1 3QR, England.
authors.forename: Alison
authors.initials: A
authors.lastname: Parkin
authors.forename: Christine
authors.initials: C
authors.lastname: Cavazza
authors.forename: Juan C
authors.initials: JC
authors.lastname: Fontecilla-Camps
authors.forename: Fraser A
authors.initials: FA
authors.lastname: Armstrong
mesh_terms: D002384:Catalysis; D045285:Desulfovibrio desulfuricans / Q000201:enzymology*; D004563:Electrochemistry; D004789:Enzyme Activation / Q000528:radiation effects; D006859:Hydrogen / Q000737:chemistry / Q000494:pharmacology* / Q000528:radiation effects; D006863:Hydrogen-Ion Concentration; D006864:Hydrogenase / Q000037:antagonists & inhibitors* / Q000737:chemistry* / Q000528:radiation effects; D007506:Iron-Sulfur Proteins / Q000037:antagonists & inhibitors* / Q000737:chemistry* / Q000528:radiation effects; D008027:Light; D008958:Models, Molecular; D010084:Oxidation-Reduction; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D011522:Protons; D013997:Time Factors
chemical_list: D007506:Iron-Sulfur Proteins; D011522:Protons; D006859:Hydrogen; C118830:iron hydrogenase; D006864:Hydrogenase