title: Two W-containing formate dehydrogenases (CO2-reductases) involved in syntrophic propionate oxidation by Syntrophobacter fumaroxidans.
abstract: Two formate dehydrogenases (CO2-reductases) (FDH-1 and FDH-2) were isolated from the syntrophic propionate-oxidizing bacterium Syntrophobacter fumaroxidans. Both enzymes were produced in axenic fumarate-grown cells as well as in cells which were grown syntrophically on propionate with Methanospirillum hungatei as the H2 and formate scavenger. The purified enzymes exhibited extremely high formate-oxidation and CO2-reduction rates, and low Km values for formate. For the enzyme designated FDH-1, a specific formate oxidation rate of 700 U.mg-1 and a Km for formate of 0.04 mm were measured when benzyl viologen was used as an artificial electron acceptor. The enzyme designated FDH-2 oxidized formate with a specific activity of 2700 U.mg-1 and a Km of 0.01 mm for formate with benzyl viologen as electron acceptor. The specific CO2-reduction (to formate) rates measured for FDH-1 and FDH-2, using dithionite-reduced methyl viologen as the electron donor, were 900 U.mg-1 and 89 U.mg-1, respectively. From gel filtration and polyacrylamide gel electrophoresis it was concluded that FDH-1 is composed of three subunits (89 +/- 3, 56 +/- 2 and 19 +/- 1 kDa) and has a native molecular mass of approximately 350 kDa. FDH-2 appeared to be a heterodimer composed of a 92 +/- 3 kDa and a 33 +/- 2 kDa subunit. Both enzymes contained tungsten and selenium, while molybdenum was not detected. EPR spectroscopy suggested that FDH-1 contains at least four [2Fe-2S] clusters per molecule and additionally paramagnetically coupled [4Fe-4S] clusters. FDH-2 contains at least two [4Fe-4S] clusters per molecule. As both enzymes are produced under all growth conditions tested, but with differences in levels, expression may depend on unknown parameters.
authors.affiliation: Laboratory of Microbiology, Wageningen University, The Netherlands. Frank.deBok@wur.nl
authors.forename: Frank A M
authors.initials: FA
authors.lastname: de Bok
authors.forename: Peter-Leon
authors.initials: PL
authors.lastname: Hagedoorn
authors.forename: Pedro J
authors.initials: PJ
authors.lastname: Silva
authors.forename: Wilfred R
authors.initials: WR
authors.lastname: Hagen
authors.forename: Emile
authors.initials: E
authors.lastname: Schiltz
authors.forename: Kathrin
authors.initials: K
authors.lastname: Fritsche
authors.forename: Alfons J M
authors.initials: AJ
authors.lastname: Stams
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism; D020564:Deltaproteobacteria / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D004583:Electrons; D004591:Electrophoresis, Polyacrylamide Gel; D005560:Formate Dehydrogenases / Q000737:chemistry* / Q000378:metabolism; D005561:Formates / Q000378:metabolism; D006859:Hydrogen / Q000378:metabolism; D007700:Kinetics; D010100:Oxygen / Q000378:metabolism*; D010269:Paraquat / Q000494:pharmacology; D011422:Propionates / Q000737:chemistry*; D017434:Protein Structure, Tertiary; D013696:Temperature
chemical_list: D005561:Formates; D011422:Propionates; C030544:formic acid; D002245:Carbon Dioxide; D006859:Hydrogen; D005560:Formate Dehydrogenases; D010269:Paraquat; D010100:Oxygen