title: A molybdenum and a tungsten isoenzyme of formylmethanofuran dehydrogenase in the thermophilic archaeon Methanobacterium wolfei.
abstract: We have recently reported that the thermophilic archaeon Methanobacterium wolfei contains two formylmethanofuran dehydrogenases, I and II. Formylmethanofuran dehydrogenase II, which is preferentially expressed in tungsten-grown cells, has been purified and shown to be a tungsten-iron-sulfur protein. We have now purified and characterized formylmethanofuran dehydrogenase I from molybdenum-grown cells and shown that it is a molybdenum-iron-sulfur protein. The purified enzyme, with a specific activity of 27 U/mg protein, was found to be composed of three subunits of apparent molecular mass 64 kDa, 51 kDa, and 31 kDa and to contain per mol 146-kDa molecule approximately 0.23 mol molybdenum, 0.46 mol molybdopterin guanine dinucleotide, and 6.6 mol non-heme iron but no tungsten (< 0.01 mol). The molybdenum enzyme differed from the tungsten enzyme (8 U/mg) in that it catalyzed the oxidation of N-furfurylformamide and formate and was inactivated by cyanide. The two enzymes also differed significantly in the pH optimum, in the apparent Km for the electron acceptor, and in the chromatographic behaviour. The molybdenum enzyme and the tungsten enzyme were similar, however, in that the N-terminal amino acid sequences determined for the alpha and beta subunits were identical up to residue 23, indicating that the two proteins are isoenzymes. The molybdenum enzyme, as isolated, was found to display an EPR signal derived from molybdenum as evidenced by isotope substitution.
authors.affiliation: Laboratorium für Mikrobiologie des Fachbereichs Biologie, Philipps-Universität, Federal Republic of Germany.
authors.forename: R A
authors.initials: RA
authors.lastname: Schmitz
authors.forename: S P
authors.initials: SP
authors.lastname: Albracht
authors.forename: R K
authors.initials: RK
authors.lastname: Thauer
mesh_terms: D000445:Aldehyde Oxidoreductases / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D000595:Amino Acid Sequence; D002384:Catalysis; D004578:Electron Spin Resonance Spectroscopy; D004591:Electrophoresis, Polyacrylamide Gel; D006863:Hydrogen-Ion Concentration; D007527:Isoenzymes / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D008667:Metalloproteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D017014:Methanobacterium / Q000201:enzymology*; D008969:Molecular Sequence Data; D008982:Molybdenum / Q000032:analysis*; D019159:Nonheme Iron Proteins; D014414:Tungsten / Q000032:analysis*
chemical_list: D007527:Isoenzymes; D008667:Metalloproteins; D019159:Nonheme Iron Proteins; D008982:Molybdenum; D000445:Aldehyde Oxidoreductases; C060639:formylmethanofuran dehydrogenase; D014414:Tungsten