title: Direct electrochemistry of a bacterial sulfite dehydrogenase.
abstract: Sulfite dehydrogenase from Starkeya novella is an alphabeta heterodimer comprising a 40.6 kDa subunit (containing the Mo cofactor) and a smaller 8.8 kDa heme c subunit. The enzyme catalyses the oxidation of sulfite to sulfate with the natural electron acceptor being cytochrome c550. Its catalytic mechanism is thought to resemble that found in eukaryotic sulfite oxidases. Using protein film voltammetry and redox potentiometry, we have identified both Mo- and heme-centered redox responses from the enzyme immobilized on a pyrolytic graphite working electrode: E m,8 (Fe III/II) +177 mV; E m,8 (Mo VI/V) +211 mV and E m,8 (Mo V/IV) -118 mV vs NHE; Upon addition of sulfite to the electrochemical cell a steady-state voltammogram is observed and an apparent Michaelis constant (Km) of 26(1) microM was determined for the enzyme immobilized on the working electrode surface, which is comparable with the value obtained from solution assays.
authors.affiliation: Department of Chemistry, Centre for Metals in Biology, University of Queensland, Brisbane, 4072, Australia.
authors.forename: Kondo-François
authors.initials: KF
authors.lastname: Aguey-Zinsou
authors.forename: Paul V
authors.initials: PV
authors.lastname: Bernhardt
authors.forename: Ulrike
authors.initials: U
authors.lastname: Kappler
authors.forename: Alastair G
authors.initials: AG
authors.lastname: McEwan
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D003579:Cytochrome Reductases / Q000737:chemistry* / Q000378:metabolism; D004563:Electrochemistry; D004566:Electrodes; D004800:Enzymes, Immobilized / Q000737:chemistry* / Q000378:metabolism; D006108:Graphite; D007501:Iron / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D008982:Molybdenum / Q000737:chemistry / Q000378:metabolism; D010084:Oxidation-Reduction; D050902:Sulfite Dehydrogenase; D013855:Thiobacillus / Q000201:enzymology*
chemical_list: D001426:Bacterial Proteins; D004800:Enzymes, Immobilized; D006108:Graphite; D008982:Molybdenum; D007501:Iron; D003579:Cytochrome Reductases; D050902:Sulfite Dehydrogenase