Effect of divalent cations on the short-term NH
4
+
inhibition of nitrogen fixation in Azotobacter chroococcum |
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Authors: | María T Ruiz Francisco J Cejudo Antonio Paneque |
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Institution: | (1) Instituto de Bioquímica Vegetal y Fotosíntesis, Universidad de Sevilla-Consejo Superior de Investigaciones Científícas, Facultad de Biología, Apartado 1113, E-41080 Sevilla, Spain;(2) Present address: The Sainsbury Laboratory, John Innes Institute, Colney Lane, NR4 7UH Norwich, UK |
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Abstract: | Incubation of Azotobacter chroococcum in the presence of micromolar concentrations of MnCl2, but not MgCl2, prevented nitrogenase activity from NH
4
+
inhibition. Mg(II), at a 100-fold concentration with respect to Mn(II), counteracted the protective effect of Mn(II) on nitrogenase activity. When Mn(II) was added to cells that had been given NH4Cl, stopping of NH
4
+
uptake and recovery of nitrogenase activity took place, and a raise of NH
4
+
concentration in medium developed. Furthermore, incubation of A. chroococcum cells with 20 M Mn(II) under air, but not under an argon: oxygen (79%:21%) gas mixture, resulted in NH
4
+
excretion to the external medium. The Mn(II)-mediated uncoupling of nitrogen fixation from ammonium assimilation leads us to conclude that Mn(II) may act as a physiological inhibitor of glutamine synthetase.Abbreviations Hepes
N-2-Hydroxyethylpiperazine-N -ethanesulfonic acid
- Mops
3-(N-Morpholino)propanesulfonic acid |
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Keywords: | Divalent cation Manganese Nitrogenase activity Glutamine synthetase Enzyme regulation Azotobacter chroococcum |
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