Isolation of auxotrophic mutants in support of ammonia assimilation via glutamine synthetase in Methanobacterium ivanovii |
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Authors: | L Bhatnagar M K Jain J G Zeikus J -P Aubert |
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Institution: | (1) Unité de Physiologie Cellulaire, Département de Biochimie et Génétique Moléculaire, Institut Pasteur, 28 rue du Dr. Roux, F-75015 Paris, France;(2) Present address: Michigan Biotechnology Institute, 410 Biochemistry Department, Michigan State University, 48824 East Lansing, MI, USA;(3) Present address: Department of Microbiology, Haryana Agricultural University, Hissar, India;(4) Present address: Department of Biochemistry and Microbiology and the Michigan Biotechnology Institute, Michigan State University, 48824 East Lansing, Michigan, USA |
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Abstract: | Various enzymes involved in the initial metabolic pathway for ammonia assimilation by Methanobacterium ivanovii were examined. M. ivanovii showed significant activity of glutamine synthetase (GS). Glutamate synthase (GOGAT) and alanine dehydrogenase (ADH) were present, wheras, glutamate dehydrogenase (GDH) was not detected. When M. ivanovii was grown with different levels of NH
+
4
(i.e. 2, 20 or 200 mM), GS, GOGAT and ADH activities varied in response to NH
+
4
concentration. ADH was not detected at 2 mM level, but its activity increased with increased levels of NH
+
4
in the medium. Both GS and GOGAT activities increased with decreasing concentrations of NH
+
4
and were maximum when ammonia was limiting, suggesting that at low NH
+
4
levels, GS and GOGAT are responsible for ammonia assimilation and at higher NH
+
4
levels, ADH might play a role. Metabolic mutants of M. ivanovii that were auxotrophic for glutamine were obtained and analyzed for GS activity. Results indicate two categories of mutants: i) GS-deficient auxotrophic mutants and ii) GS-impaired auxotrophic mutants.Abbreviations GS
Glutamine synthetase
- GOGAT
glutamate synthase
- GDH
glutamate dehydrogenase
- ADH
alanine dehydrogenase |
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Keywords: | Methanobacterium Ammonia assimilation enzymes GS-GOGAT pathway NH
+
4
regulation M ivanovii glutamine auxotrophs |
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