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2001 (1)
1993 (1)
1Author    JohnG. Palmer, PaulA. Doemeny, GerhardN. SchrauzerRequires cookie*
 Title    The Chemical Evolution of a Nitrogenase Model, XXIII. The Nature of the Active Site and the Role of Homocitric Acid in MoFe-Nitrogenase  
 Abstract    The iron-molybdenum cofactor (FeMo-co) of bacterial nitrogenase is a heterometallic cluster of composition MoFe7S9 that is attached to the apoprotein by a coordinative Mo-N bond to the imidazole group of hisa442, and by a Fe-S bond to cysa.215. The molybdenum atom of FeMo-co in the enzyme in addition is coordinated to one molecule of homocitrate (he), which is required for maximal N2 reducing activity. The molybdenum atom in the enzyme-bound FeMo-co thus is hexacoordinated and cannot react with substrates unless free coordination sites are made available. It is proposed that the reactions of the substrates o f nitrogenase occur at a molybdenum active site consisting of a mononuclear molybdenum homocitrate complex attached to hisaAA2 of the apoprotein that in the functional enzyme is generated from FeMo-co by a reversible, redox-linked dissociation of the Fe7S9-c;y5' cluster. Studies with catalytic model systems consisting of complexes of molybdenum with imidazole and hydroxo-carboxylate ligands support this proposal and provide a rationale for the specific activating effect of homocitrate in nitrogenase. 
  Reference    Z. Naturforsch. 56b, 386—393 (2001); received January 17 2001 
  Published    2001 
  Keywords    Nitrogen, Acetylene, Homocitric Acid 
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 TEI-XML for    default:Reihe_B/56/ZNB-2001-56b-0386.pdf 
 Identifier    ZNB-2001-56b-0386 
 Volume    56 
2Author    G. Erhard, N. Schrauzer, PaulA. Doemeny, JohnG. PalmerRequires cookie*
 Title    The Chemical Evolution o f a Nitrogenase Model, XXII. Reduction of Acetylene with Catalysts Derived from Molybdate, Homocitric Acid and N-M ethylimidazole and a Proposal Concerning the Active Site of Functional Azotobacter Nitrogenases  
 Abstract    Based on model experiments it is suggested that the reduction o f substrates by nitrogenase occurs at a m ononuclear site containing molybdenum, homocitrate and the imidazole com ponent of his-442 o f the apoenzyme, generated from the FeMo-co by a reversible dissociation of the Fe7S8 unit from the M oFe7S8 cluster in a redox-linked process. 
  Reference    Z. Naturforsch. 48b, 1295—1298 (1993); received May 14 1993 
  Published    1993 
  Keywords    Nitrogenase, Acetylene Reduction, M olybdenum-Catalyzed, Homocitric Acid, Histidine, Imidazole 
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 TEI-XML for    default:Reihe_B/48/ZNB-1993-48b-1295_n.pdf 
 Identifier    ZNB-1993-48b-1295_n 
 Volume    48