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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Archives of microbiology 132 (1982), S. 79-81 
    ISSN: 1432-072X
    Keywords: Ammonium transport ; Regulation ; Rhodospirillum rubrum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract An ammonium transport system in the phototrophic N2-fixing bacteriumRhodospirillum rubrum was characterized by using the uptake of14C-methylamine as a probe. Uptake showed saturation kinetics with an apparentK m =110 μM. It was competitively inhibited by ammonium (K i =7 μM). Uptake exhibited a narrow pH maximum around pH 7.0. Up to 200-fold gradients across the membrane were formed within 40–60 min. Gradient formation was inhibited by carbon starvation, azide or cyanide. Pre-accumulated methylamine was released by ammonium pulses to more than 80%, indicating only minor metabolization. The synthesis of the transport system was repressed by ammonium in high concentrations.
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  • 2
    ISSN: 1432-072X
    Keywords: Clostridium thermosaccharolyticum ; Clostridium thermoautotrophicum ; Thermophilic nitrogenase ; Ammonium assimilation ; Nitrogen control
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Inorganic nitrogen metabolism in the obligate anaerobic thermophiles Chlostridium thermosaccharolyticum and Clostridium thermoautotrophicum differs in several respects. C. thermosaccharolyticum contains a nitrogenase as inferred from NH 4 + repressible C2H2 reduction, a glutamine synthetase which is partially repressed by ammonium, very labile glutamate synthase activities with both NADH and NADPH, NADPH-dependent glutamate dehydrogenase, and NH 4 + -dependent asparagine synthetase. C. thermoautotrophicum contains no nitrogenase, but glutamine synthetase, no glutamate synthase, no glutamate dehydrogenase, but a NADH-dependent alanine dehydrogenase and a NH 4 + -dependent asparagine synthetase.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Archives of microbiology 145 (1986), S. 287-289 
    ISSN: 1432-072X
    Keywords: Azotobacter vinelandii ; Encystment ; Nitrogenase ; Protein degradation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Nitrogenase activity in cell-free extracts of Azotobacter vinelandii declines during encystment. Upon germination a rapid increase in activity is observed, which is suppressed by rifampicin, suggesting that de novo biosynthesis of the nitrogenase proteins is required. The decline of activity during encystment is accompanied by disappearance of both nitrogenase proteins from cell extracts, indicating irreversible proteolysis. Total proteinase activity does not change significantly during encystment.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Archives of microbiology 149 (1988), S. 377-383 
    ISSN: 1432-072X
    Keywords: Urea uptake ; Alcaligenes eutrophus H16 ; Klebsiella pneumoniae ; Pseudomonas aeruginosa ; Providencia rettgeri ; Proteus vulgaris ; Bacillus pasteurii ; Nitrogen control
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Evidence for the existence of an energy-dependent urea permease was found for Alcaligenes eutrophus H16 and Klebsiella pneumoniae M5a1 by studying uptake of 14C-urea. Since intracellular urea was metabolized immediately, uptake did not result in formation of an urea pool. Evidence is based on observations that the in vivo urea uptake and in vitro urease activity differ significantly with respect to kinetic parameters, temperature optimum, pH optimum, response towards inhibitors and regulation. The K m for urea uptake was 15–20 times lower (38 μM and 13 μM urea for A. eutrophus and K. pneumoniae, respectively) than the K m of urease for urea (650 μM and 280 μM urea), the activity optimum for A. eutrophus was at pH 6.0 and 35°C for the uptake and pH 9.0 and 65°C for urease. Uptake but not urease activity in both organisms strongly decreased upon addition of inhibitors of energy metabolism, while in K. pneumoniae, potent inhibitors of urease (thiourea and hydroxyurea) did not affect the uptake process. Significant differences in the uptake rates were observed during growth with different nitrogen sources (ammonia, nitrate, urea) or in the absence of a nitrogen source; this suggested that a carrier is involved which is subject to nitrogen control. Some evidence for the presence of an energy-dependent uptake of urea was also obtained in Pseudomonas aeruginosa DSM 50071 and Providencia rettgeri DSM 1131, but not in Proteus vulgaris DSM 30118 and Bacillus pasteurii DSM 33.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Archives of microbiology 133 (1982), S. 239-241 
    ISSN: 1432-072X
    Keywords: Rhodsopirillaceae ; Ammonium transport ; Nitrogenase ; Nitrate reduction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Regulatory aspects of the assimilation of inorganic nitrogen compounds (ammonia, nitrate, nitrogen) were studied in 12 strains belonging to the Rhodospirillaceae. All strains possessed an ammonium transport system, as demonstrated by 14C-methylammonium uptake. This uptake showed saturation kinetics (K m between 50–150 μM), and was competitively inhibited by ammonium (K i between 5–18 μM). The ammonium transport systems were repressed by ammonium in the growth medium. The nitrogenase activity of all strains was reversibly inhibited by ammonium (“switch-off”). This effect was not shown under nitrogen starvation conditions with the exception of some strains of Rhodopseudomonas capsulata, the nitrogenase of which was always susceptible to switch-off by ammonium. Assimilation of nitrate was confined to some strains of Rhodopseudomonas capsulata.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Archives of microbiology 139 (1984), S. 245-247 
    ISSN: 1432-072X
    Keywords: Klebsiella pneumoniae ; Amt - mutant ; Ammonium excretion ; Ammonium transport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The main property of an Amt- (ammonium transport negative) mutant of Klebsiella pneumoniae is its inability to accumulate NH 4 + intracellularly. When growing on nitrogen sources other than NH 4 + , the mutant constantly looses NH3 by diffusion. This loss results in poor growth. The NH3 excretion suggests the existence of a futile cycle (NH3 loss/NH 4 + reabsorption) in the wild type and possibly other bacterial strains, which do not constantly excrete NH3.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Archives of microbiology 142 (1985), S. 285-288 
    ISSN: 1432-072X
    Keywords: Paracoccus denitrificans ; Methylammonium transport ; Ammonium transport ; Nitrogen control ; Carbon control
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Depending on the growth conditionsParacoccus denitrificans synthesizes two different carriers mediating uptake of methylamine. When used as a nitrogen source, methylamine is transported via a NH 4 + carrier, and its transport is inhibited by NH 4 + but not by ethylamine. When used as a carbon source, methylamine is transported by a specific alkylamine carrier, and its transport is inhibited by ethylamine but not by NH 4 + . The NH 4 + carrier is under nitrogen control, the alkylamine carrier under carbon control.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Archives of microbiology 145 (1986), S. 306-310 
    ISSN: 1432-072X
    Keywords: Ammonium uptake ; Methylammonium ; Nitrogen control ; Cold shock ; Alcaligenes eutrophus H16
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The uptake of the radioactive ammoniumanalogue 14C-methylammonium1 was measured in heterotrophically grown cells of Alcaligenes eutrophus H16 in order to study the mechanism of NH 4 + uptake. MA gradients of up to 200 were built up by a substrate-specific and energy-dependent system which showed a K m of 35–111 μM and a V max of 0.4–1.8 nmol MA/min per mg protein. The involved carrier exhibited a higher affinity towards NH 4 + than towards CH3NH 3 + indicating that ammonium rather than MA was its natural substrate. Cold shock with hypotonic but not with hypertonic solutions caused the efflux of almost the entire accumulated MA. Osmotic shock did not affect the uptake reaction, suggesting that no periplasmic binding proteins were involved. Indirect observations indicate the membrane potential as driving force for MA uptake. High rates of uptake were observed in cells grown under nitrogen deficiency or with nitrate as nitrogen source. The uptake rate decreased during growth at high ammonium concentrations indicating that biosynthesis of nitrogenous compounds was supported by passive diffusion of NH3. The data suggest that the formation of the carrier is subject to “nitrogen control”.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Archives of microbiology 145 (1986), S. 159-161 
    ISSN: 1432-072X
    Keywords: Clostridium cellobioparum ; Clostridium thermocellum ; Ammonium assimilation ; Nitrogen fixation ; Nitrogen control
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Inorganic nitrogen metabolism in two cellulose degrading clostridia, the mesophile Clostridium cellobioparum and the thermophile Clostridium thermocellum was investigated. Both strains show acetylene reduction (i.e. possibly nitrogenase activity), contain glutamine synthetase, glutamate dehydrogenase and glutamate-dependent transaminases. C. cellobioparum additionally contains a NADH-dependent glutamate synthase and a NH 4 + -repressible glycine dehydrogenase (NADPH). Remarkably, acetylene reduction in C. thermocellum is not repressed by ammonium, casting doubt whether this activity is due to nitrogenase. The results are compared with the data from other saccharolytic clostridia.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Archives of microbiology 166 (1996), S. 388-393 
    ISSN: 1432-072X
    Keywords: Ammonium metabolism ; glnAntrBC ; Nitrogenase regulation ; Nitrogen control ; Ammonia excretion ; Amino acid utilization ; Ntr
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Enterobacterial mutants defective in the nitrogen control regulatory system (Ntr) generally display a pleiotropic phenotype with regard to expression and regulation of several enzymes and transport systems involved in the assimilation of N sources. This report describes the isolation and characterization of similar pleiotropic mutants ofKlebsiella pneumoniae that cannot be complemented byntr genes. The strains excreted ammonia, were unable to grow on a number of N sources, and contained low glutamine:2-oxoglutarate amino transferase and normal, but unmodifiable glutamine synthetase activities and a nitrogenase level largely unaffected by ammonium, but still repressible by an amino acid mixture. Genetic studies suggested that this phenotype is due to overexpression of an unknown regulatory protein.
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