title: Thermodynamics of the formylmethanofuran dehydrogenase reaction in Methanobacterium thermoautotrophicum.
abstract: Purified formylmethanofuran dehydrogenase from Methanobacterium thermoautotrophicum, which is a thermophilic methanogenic Archaeon growing on H2 and CO2, was shown to catalyze the reversible reduction of CO2 to N-formylmethanofuran with 1,1',2,2'-tetramethylviologen (E'0 = -550 mV) as electron donor. The rate of CO2 reduction was approximately 25 times higher than the rate of N-formylmethanofuran dehydrogenation. From determinations of equilibrium concentrations at 60 degrees C and pH 7.0 a midpoint potential (E'0) for the CO2 + methanofuran/formylmethanofuran couple of approximately -530 mV was estimated. The initial step of methanogenesis from CO2 thus has a midpoint potential considerably more negative than that of the H+/H2 couple (E'0 = -460 mV at 60 degrees C). Evidence is described indicating that the as-yet unidentified physiological electron donor of the formylmethanofuran dehydrogenase is present in the soluble cell fraction.
authors: Max-Planck-Institut für terrestrische Mikrobiologie Marburg, Philipps-Universität Marburg, Germany.
authors: P A
authors: PA
authors: Bertram
authors: R K
authors: RK
authors: Thauer
mesh_terms: D000445:Aldehyde Oxidoreductases / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D005663:Furans / Q000378:metabolism; D007700:Kinetics; D017014:Methanobacterium / Q000201:enzymology*; D010084:Oxidation-Reduction; D010269:Paraquat / Q000031:analogs & derivatives / Q000378:metabolism; D013816:Thermodynamics
chemical_list: D005663:Furans; D002245:Carbon Dioxide; C091384:1,1',2,2'-tetramethylviologen; C050842:formylmethanofuran; D000445:Aldehyde Oxidoreductases; C060639:formylmethanofuran dehydrogenase; D010269:Paraquat