In vitro synthesis of the iron-molybdenum cofactor and its analogs: Requirement of a non-nif gene product for the synthesis, and altered properties of dinitrogenase

  • Vinod K. Shah
  • Mark S. Madden
  • Paul W. Ludden


Nitrogenase catalyzes the ATP- and reductant-dependent reduction of N2 to ammonia and the reduction of other substrates (i.e. acetylene, cyanide). In the absence of any reducible substrate, nitrogenase catalyzes the reduction of protons to H2. Nitrogenase consists of two proteins, dinitrogenase (MoFe protein, component I) and dinitrogenase reductase (Fe protein, component II) (1,5). Dinitrogenase reductase donates electrons one at a time to dinitrogenase with the concomitant hydrolysis of ATP. Electrons passed to dinitrogenase are channelled to a unique prosthetic group called the iron-molybdenum cofactor (FeMo-co) which is composed of Fe, Mo, S, (27) and homocitrate (10). FeMo-co has been proposed as the site for substrate reduction (6, 28). In Klebsiella pneumoniae, at least six nif (nitrogen fixation) gene products (NIF Q, NIF B, NIF V, NIF N, NIF E, and dinitrogenase reductase) are involved in the synthesis of active FeMo-co. The NIF Q is required for early steps in the processing of Mo for FeMo-co biosynthesis (11). Mutations in nif B, nif N, or nif E result in formation of an apo-dinitrogenase (lacking FeMo-co), that can be activated in vitro with purified FeMo-co (24,27,31). Certain strains of K. pneumoniae and Azotobacter vinelandii with mutations in nif H (the structural gene for dinitrogenase reductase) fail to synthesize FeMo-co (4,25).


Nitrogen Fixation Hydroxy Group Racemic Mixture Carboxy Group ENDOR Spectrum 
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Copyright information

© Routledge, Chapman & Hall, Inc. 1990

Authors and Affiliations

  • Vinod K. Shah
    • 1
  • Mark S. Madden
    • 1
  • Paul W. Ludden
    • 1
  1. 1.Department of Biochemistry and Center for the Study of Nitrogen Fixation, College of Agricultural and Life SciencesUniversity of Wisconsin-MadisonMadisonUSA

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