title: N2 fixation by Streptomyces thermoautotrophicus involves a molybdenum-dinitrogenase and a manganese-superoxide oxidoreductase that couple N2 reduction to the oxidation of superoxide produced from O2 by a molybdenum-CO dehydrogenase.
abstract: N2 fixation by Streptomyces thermoautotrophicus follows the equation N2 + 4-12MgATP + 8H+ + 8e- --> 2NH3 + H2 + 4-12MgADP + 4-12Pi and exhibits features which are not obvious in the diazotrophic bacteria studied so far. The reaction is coupled to the oxidation of carbon monoxide (CO) by a molybdenum-containing CO dehydrogenase that transfers the electrons derived from CO oxidation to O2, thereby producing superoxide anion radicals (O-2). A manganese-containing superoxide oxidoreductase reoxidizes the O-2 anions to O2 and transfers the electrons to a MoFeS-dinitrogenase for the reduction of N2 to ammonium. Among the most striking properties of the S. thermoautotrophicus nitrogenase system are the dependence on O2 and O-2, the complete insensitivity of all components involved toward O2 and H2O2, the inability to reduce ethine or ethene, and a low MgATP requirement. In addition, the subunit structure of the S. thermoautotrophicus nitrogenase components and the polypeptides involved seem to be dissimilar from the known nitrogenases.
authors.affiliation: Lehrstuhl für Mikrobiologie, Universität Bayreuth, D-95440 Bayreuth, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Ribbe
authors.forename: D
authors.initials: D
authors.lastname: Gadkari
authors.forename: O
authors.initials: O
authors.lastname: Meyer
mesh_terms: D000445:Aldehyde Oxidoreductases / Q000378:metabolism*; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000378:metabolism; D002384:Catalysis; D006861:Hydrogen Peroxide / Q000378:metabolism; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000378:metabolism*; D009586:Nitrogen Fixation; D009591:Nitrogenase / Q000378:metabolism*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D013056:Spectrophotometry, Ultraviolet; D013302:Streptomyces / Q000201:enzymology / Q000378:metabolism*; D013482:Superoxide Dismutase / Q000378:metabolism*; D013481:Superoxides / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D009097:Multienzyme Complexes; D013481:Superoxides; D006861:Hydrogen Peroxide; D013482:Superoxide Dismutase; D009591:Nitrogenase; D000445:Aldehyde Oxidoreductases; C019823:carbon monoxide dehydrogenase; D010100:Oxygen