Derepression of nitrogenase synthesis in the presence of excess NH4+

Gordon, Joyce K.; Brill, Winston J.

doi:10.1016/s0006-291x(74)80074-4

Cited by 103 publications

(40 citation statements)

References 11 publications

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“…The intracellular glutamine level has previously been suggested to be a metabolic signal that could regulate the nitrogen metabolism in several organisms (7,11,23). In Synechocystis sp., the intracellular concentration of glutamine is only slightly affected by the available nitrogen source (Table 1); therefore, it is not likely to play such a regulatory role.…”

Section: Resultsmentioning

confidence: 99%

Regulation of glutamine synthetase activity in the unicellular cyanobacterium Synechocystis sp. strain PCC 6803 by the nitrogen source: effect of ammonium

1991

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Glutamine synthetase activity from Synechocystis sp. strain PCC 6803 is regulated as a function of the nitrogen source available in the medium. Addition of 0.25 mM NH4Cl to nitrate-grown cells promotes a clear short-term inactivation of glutamine synthetase, whose enzyme activity decreases to 5 to 10% of the initial value in 25 min. The intracellular levels of glutamine, determined under various conditions, taken together with the results obtained with azaserine (an inhibitor of transamidases), rule out the possibility that glutamine per se is responsible for glutamine synthetase inactivation. Nitrogen starvation attenuates the ammonium-mediated glutamine synthetase inactivation, indicating that glutamine synthetase regulation is modulated through the internal balance between carbon-nitrogen compounds and carbon compounds. The parallelism observed between the glutamine synthetase activity and the internal concentration of a-ketoglutarate suggests that this metabolite could play a role as a positive effector of glutamine synthetase activity in Synechocystis sp. Despite the similarities of this physiological system to that described for enterobacteria, the lack of in vivo 32p labeling of glutamine synthetase during the inactivation process excludes the existence of an adenylylation-deadenylylation system in this cyanobacterium.Glutamine synthetase (GS; EC 6.3.1.2) plays a central role in nitrogen metabolism by prokaryotes. This central role requires that both the synthesis and activity of this enzyme be strictly regulated in response to the available nitrogen source. In enterobacteria this regulation takes place at two different levels, first by modulating enzyme activity by an adenylylation-deadenylylation system (35) and second by regulating GS synthesis through transcription from different promoters (18). The adenylylation of GS makes it more susceptible to a cumulative feedback inhibition by metabolites derived from ammonium assimilation, such as amino acids or nucleotides (35). In contrast, most of the grampositive bacteria lack this system, and the regulation of the enzyme appears to involve a single feedback mechanism, in which GS is strongly inhibited by glutamine (5,14).In cyanobacteria, ammonium assimilation takes place mainly by the sequential action of GS and glutamate synthase (GOGAT) (GS-GOGAT pathway) (21). The regulation of GS synthesis in Anabaena sp. strain PCC 7120 has been well characterized; several promoters have been found for the structural GS gene, ginA (37). Selective transcription from these promoters determines that in ammonium-grown cells the level of GS protein is about 50% lower than that observed under dinitrogen-fixing conditions (37). Recently, we have reported a repression of GS synthesis by ammonium in the cyanobacteria Synechocystis sp. and Calothrix sp. (22).The existence of an adenylylation-deadenylylation system, as observed in the majority of gram-negative bacteria, has been previously discounted for the genus Anabaena (8), and it has been proposed that regulation of GS act...

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Section: Resultsmentioning

confidence: 99%

Regulation of glutamine synthetase activity in the unicellular cyanobacterium Synechocystis sp. strain PCC 6803 by the nitrogen source: effect of ammonium

1991

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“…MSX is an inhibitor of glutamine synthetase, and its addition can cause the derepression of the nitrogenase enzyme in the presence of NHZ (Gordon & Brill 1974). Stimulation of nitrogenase activity in the presence of MSX would suggest that in situ N2 fixation is occurring at levels below full potential due to repression by NHf; (Yoch & Whiting 1986, Capone 1988.…”

Section: Methodsmentioning

confidence: 99%

Nitrogenase activity in tropical carbonate marine sediments

O’Neil¹,

Capone²

1989

Mar. Ecol. Prog. Ser.

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Rates of nitrogenase acbvity were investigated in carbonate sediments of shallow tropical waters uslng the acetylene (C2H2) reduction method Nitrogenase achvlty was significantly h g h e r in fine grained sedments than m coarser grained sands The importance of oxygen, ammonium (NH:) and organic substrate availability in regulating nitrogenase activ~ty in these sedlments was evaluated The effect of O2 was vanable and appeared to be influenced by physical dsturbance of the sediment Ammonium did not appear to inhibit rates of N2 fixation over the range of in situ concentrahons observed, as there was no significant correlation of N2 fixation rates and pore water NH: Neither additions of NH: nor MSX (L-methonlne-DL-sulfoxlmine a nltrogenase derepressor) had any consistent effect on N, flxatlon N2 fixation rates were correlated w t h total organlc content of sediments Additions of mannltol and glucose led to significant, concentrahon-dependent stimulation of N2 fixahon We therefore conclude that organic substrate avallabllity is a malor factor controlling rates of nitrogenase activlty in these shallow carbonate sediments Based on our experiments benthic heterotrophic bactena in carbonate sediments could account for d d y N2 fixation lnputs of 0 07 to 5 2 mg N m-2 (0 03 to 1 9 g N m yr-l) These estimates indicate that the extensive areas of carbonate sedlments in these environments may contnbute a substant~al amount of nitrogen to shallow tropical and subtropical ecosystems

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“…(ii) Addition of amino acids to the growth medium repressed nitrogenase synthesis even in nitrogenase-derepressed mutant strains (30). (iii) Inhibition of glutamine synthetase, a primary enzyme responsible for NH4+ assimilation, by a substrate (glutamate) analog, Lmethionine-D,L-sulfoximine (MSX) as well as by other inhibitors led to derepression of nitrogenase synthesis in the presence of NH4+ in all organisms tested (8,13,14,21,31,39). The above described derepression of nitrogenase synthesis is achieved by alteration of cellular physiology leading to a decrease in the rate of glutamate production, since addition of amino acids to the medium reversed the effect (22,29).…”

mentioning

confidence: 99%

Isolation and characterization of nitrogenase-derepressed mutant strains of cyanobacterium Anabaena variabilis

Spiller¹,

Latorre²,

Hassan³

et al. 1986

J Bacteriol

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A positive selection method for isolation of nitrogenase-derepressed mutant strains of a filamentous cyanobacterium, Anabaena variabilis, is described. Mutant strains that are resistant to a glutamate analog, L-methionine-D,L-sulfoximine, were screened for their ability to produce and excrete NH4' into medium.Mutant strains capable of producing nitrogenase in the presence of NH4' were selected from a population of NH4+-excreting mutants. One of the mutant strains (SA-1) studied in detail was found to be a conditional glutamine auxotroph requiring glutamine for growth in media containing N2, N03 , or low concentrations of NH4' (less than 0.5 mM). This glutamine requirement is a consequence of a block in the assimilation of NH4' produced by an enzyme system like nitrogenase. Glutamate and aspartate failed to substitute for glutamine because of a defect in the transport and utilization of these amino acids. Strain SA-1 assimilated NH4' when the concentration in the medium reached about 0.5 mM, and under these conditions the growth rate was similar to that of the parent. Mutant strain SA-1 produced L-methionine-D,L-sulfoximine-resistant glutamine synthetase activity. Kinetic properties of the enzyme from the parent and mutant were similar. Mutant strain SA-1 can potentially serve as a source of fertilizer nitrogen to support growth of crop plants, since the NH4' produced by nitrogenase, utilizing sunlight and water as sources of energy and reductant, respectively, is excreted into the environment.In free-living, nitrogen-fixing organisms, nitrogenase synthesis and activity are regulated by the presence of NH4' in the medium (3,10,31,45). That NH4+-mediated regulation of nitrogenase synthesis is not exerted by NH4+ itself but is actually a consequence of metabolic products of NH4+ assimilation has been revealed by several lines of evidence.(i) Mutant strains incapable of NH4' assimilation were derepressed for nitrogenase synthesis in the presence of NH4+ (28,31,43,44). (ii) Addition of amino acids to the growth medium repressed nitrogenase synthesis even in nitrogenase-derepressed mutant strains (30). (iii) Inhibition of glutamine synthetase, a primary enzyme responsible for NH4+ assimilation, by a substrate (glutamate) analog, Lmethionine-D,L-sulfoximine (MSX) as well as by other inhibitors led to derepression of nitrogenase synthesis in the presence of NH4+ in all organisms tested (8,13,14,21,31,39). The above described derepression of nitrogenase synthesis is achieved by alteration of cellular physiology leading to a decrease in the rate of glutamate production, since addition of amino acids to the medium reversed the effect (22,29). This set of conditions also derepressed other NH4+-as well as glutamate-producing enzyme systems (NO3 assimilation; histidine and proline utilization) in the cell (16,29).Mutant strains that are blocked at the level of NH4+ assimilation were first described in Klebsiella pneumoniae (32), and such mutant strains not only derepress nitrogenase synthesis but also excrete the NH4+ produce...

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Derepression of nitrogenase synthesis in the presence of excess NH4+

Cited by 103 publications

References 11 publications

Regulation of glutamine synthetase activity in the unicellular cyanobacterium Synechocystis sp. strain PCC 6803 by the nitrogen source: effect of ammonium

Regulation of glutamine synthetase activity in the unicellular cyanobacterium Synechocystis sp. strain PCC 6803 by the nitrogen source: effect of ammonium

Nitrogenase activity in tropical carbonate marine sediments

Isolation and characterization of nitrogenase-derepressed mutant strains of cyanobacterium Anabaena variabilis

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