title: Feedback inhibition of nitrogenase.
abstract: No inhibition of nitrogenase activity by physiological levels of NH4+ or carbamyl phosphate was observed in extracts of Azotobacter vinelandii. All of the 15N2 reduced by cultures which received no NH4+ was found in the cells. By contrast, more than 95% of the 15N2 reduced by cultures which had been given NH4+ was found in the medium. Failure to examine the culture medium would lead to the erroneous conclusion that N2 fixation is inhibited by NH4+. Nitrogenase in a derepressed mutant strain of A. vinelandii was fully active in vivo in the presence of NH4+. The addition of NH4Cl to N2-fixing cultures resulted in no decrease in the N2-reducing activity of intact cells of Klebsiella pneumoniae or Clostridium pasteurianum and only a small (15%) decrease in A. vinelandii. Therefore, no significant inhibition of nitrogenase by NH4+ or metabolites derived from NH4+ exists in A. vinelandii, K. pneumoniae, or C. pasteurianum.
mesh_terms: D000643:Ammonium Chloride / Q000494:pharmacology*; D001395:Azotobacter / Q000201:enzymology*; D002221:Carbamyl Phosphate / Q000494:pharmacology; D003013:Clostridium / Q000201:enzymology*; D003470:Culture Media / Q000032:analysis; D007711:Klebsiella pneumoniae / Q000201:enzymology*; D009586:Nitrogen Fixation; D009591:Nitrogenase / Q000037:antagonists & inhibitors*
chemical_list: D003470:Culture Media; D000643:Ammonium Chloride; D002221:Carbamyl Phosphate; D009591:Nitrogenase