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Ammonia assimilation pathways in Rhodopseudomonas capsulata E1F1

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Rhodopseudomonas capsulata E1F1 growing phototrophically in different inorganic nitrogen sources assimilated ammonia through the reactions of the glutamine synthetase/glutamate synthase (GS/GOGAT) pathway. Addition of either methionine sulphoximine (MSX) or azaserine to N2-fixing cells resulted in the cessation of growth, which did not occur when these inhibitors were added to bacteria growing on l-glutamate. In nitrate-assimilating cells MSX or azaserine prevented both growth and nitrate uptake with simultaneous excretion of ammonia to the medium. In addition, MSX inactivated glutamine synthetase but neither glutamate synthase nor nitrate reductase, which, in contrast, were inactivated by azaserine. The excreted ammonia was taken up together with nitrate once growth was resumed, this uptake being coincident with the appearance of an NADPH-linked alanine dehydrogenase aminating activity and a marked increase of alanine: 2-oxoglutarate aminotransferase levels.

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Glutamine synthetase


glutamate synthase


glutamate dehydrogenase


alanine dehydrogenase


l-alanine: 2-oxoglutarate aminotransferase


l-alanine: glyoxylate aminotransferase


l-alanine: oxalacetate aminotransferase




2-(N-morpholine propane sulfonate




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Correspondence to J. Cárdenas.

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Moreno-Vivián, C., Cejudo, F.J., Cárdenas, J. et al. Ammonia assimilation pathways in Rhodopseudomonas capsulata E1F1. Arch. Microbiol. 136, 147–151 (1983).

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Key words

  • Ammonia assimilation
  • l-Alanine dehydrogenase
  • l-Alanine: 2-oxoglutarate aminotransferase
  • R. capsulata E1F1