Regulation of nitrogen fixation. Nitrogenase-derepressed mutants of Klebsiella pneumoniae

Biochim Biophys Acta. 1975 Nov 11;408(2):101-11. doi: 10.1016/0005-2728(75)90002-x.


1. A new procedure is described for selecting nitrogenase-derepressed mutants based on the method of Brenchley et al. (Brenchley, J.E., Prival, M.J. and Magasanik, B. (1973) J. Biol. Chem. 248, 6122-6128) for isolating histidase-constitutive mutants of a non-N2-fixing bacterium. 2. Nitrogenase levels of the new mutants in the presence of NH4+ were as high as 100% of the nitrogenase activity detected in the absence of NH4+. 3. Biochemical characterization of these nitrogen fixation (nif) derepressed mutants reveals that they fall into three classes. Three mutants (strains SK-24, 28 and 29), requiring glutamate for growth, synthesize nitrogenase and glutamine synthetase constitutively (in the presence of NH4+). A second class of mutants (strains SK-27 and 37) requiring glutamine for growth produces derepressed levels of nitrogenase activity and synthesized catalytically inactive glutamine synthetase protein, as determined immunologically. A third class of glutamine-requiring, nitrogenase-derepressed mutants (strain SK-25 and 26) synthesizes neither a catalytically active glutamine synthetase enzyme nor an immunologically cross-reactive glutamine synthetase protein. 4. F-prime complementation analysis reveals that the mutant strains SK-25, 26, 27, 37 map in a segment of the Klebsiella chromosome corresponding to the region coding for glutamine synthetase. Since the mutant strains SK-27 and SK-37 produce inactive glutamine synthetase protein, it is concluded that these mutations map within the glutamine synthetase structural gene.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Ammonia / pharmacology
  • Chromosome Mapping
  • Glutamate Dehydrogenase / metabolism
  • Glutamate-Ammonia Ligase / immunology
  • Glutamate-Ammonia Ligase / metabolism
  • Hybridization, Genetic
  • Immunodiffusion
  • Klebsiella pneumoniae / drug effects
  • Klebsiella pneumoniae / metabolism*
  • Mutation
  • Nitrogen Fixation* / drug effects
  • Nitrogenase / metabolism*
  • Phenotype
  • Species Specificity


  • Ammonia
  • Nitrogenase
  • Glutamate Dehydrogenase
  • Glutamate-Ammonia Ligase