Regulation of the Assimilation of Nitrogen Compounds

Tyler, Bonnie

doi:10.1146/annurev.bi.47.070178.005403

Cited by 348 publications

(184 citation statements)

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“…This role of glutamine synthetase in nitrogen catabolite repression has first been found in Kleh.riel1t aerogenes [14,15] and was also reported for other enteric bacteria (reviewed in [4]). …”

supporting

confidence: 63%

Regulation of Glutamine Synthetase from Saccharomyces cerevisiae by Repression, Inactivation and Proteolysis

Legrain

Vissers

Dubois

et al. 1982

European Journal of Biochemistry

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Glutamine synthetase activity is modulated by nitrogen repression and by two distinct inactivation processes. Addition of glutamine to exponentially grown yeast leads to enzyme inactivation. 50% of glutamine synthetase activity is lost after 30min (a quarter of the generation time). Removing glutamine from the growth medium results in a rapid recovery of enzyme activity. A regulatory mutation (gdhCR mutation) suppresses this inactivation by glutamine in addition to its derepressing effect on enzymes involved in nitrogen catabolism. The gdhCR mutation also increases the level of proteinase B in exponentially grown yeast. Inactivation of glutamine synthetase is also observed during nitrogen starvation. This inactivation is irreversible and consists very probably of a proteolytic degradation. Indeed, strains bearing proteinase A, B and C mutations are no longer inactivated under nitrogen starvation.Glutamine synthetase has a central significance in nitrogen metabolism since it links the diverse catabolic processes which lead to ammonia, glutamate and 2-oxoglutarate production with the biosynthetic routes of nitrogen assimilation in proteins, nucleic acids, complex polysaccharides and somes vitamins. It might thus be expected that the activity of glutamine synthetase would be regulated so that the quantity of glutamine available for various metabolic pathways could be strictly controlled. Indeed the studies on the regulation of Escherichia coli glutaniine synthetase have shown that this enzyme is subject to modulation by mechanisms that involve covalent attachment of adenyl groups, which proceeds through a cascade system of enzymes, and cumulative feedback inhibition by the end-products of glutamine metabolism (reviewed in [I]). Such a mechanism of covalent modification of the enzyme regulates the glutamine synthetase activity in several gram-negative bacteria [2-41 and has also been shown for at least one gram-positive bacterium, Streptomyces cattleya [5].Quite different regulatory mechanisms appear to function in relation to the glutamine synthetase in eukaryotic organisms. In mammals, glutamine synthetases do not exist in adenylylated forms and many of the inhibitors of the bacterial enzymes are without effect on mammalian enzymes. The relatively high concentrations of glutamine exhibited by many mammalian tissues suggest that the regulation of glutamine synthetase in those tissues may be less important than it is in bacteria [6].Regulation of glutaniine synthetase has also been studied in two lower eukaryotes, the yeast Candida utilis and the fungus Neurospora crassu. In those two organisms the concentration of the enzyme is regulated by repression/derepression and its activity is modulated by a glutamine-mediated inactivation [7,8]. In both cases it seems that this inactivation is achieved by enzyme degradation. In C. utilis this degradation is preceded by the reversible dissociation of the enzyme [9 -1 1 1.

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supporting

confidence: 63%

Regulation of Glutamine Synthetase from Saccharomyces cerevisiae by Repression, Inactivation and Proteolysis

Legrain

Vissers

Dubois

et al. 1982

European Journal of Biochemistry

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“…It is known that GS is a hotspot in nitrogen metabolism, distributing nitrogen in glutamine form to the whole metabolic network (Tyler, 1978;Reitzer, 2003). Likewise, there is a significant ratio of EFMs that goes through the AlaDH pathway.…”

Section: Is Nitrogen Assimilated Via Aladh In Free-living State?mentioning

confidence: 99%

Metabolic analysis of Chlorobium chlorochromatii CaD3 reveals clues of the symbiosis in ‘Chlorochromatium aggregatum’

et al. 2013

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A symbiotic association occurs in 'Chlorochromatium aggregatum', a phototrophic consortium integrated by two species of phylogenetically distant bacteria composed by the green-sulfur Chlorobium chlorochromatii CaD3 epibiont that surrounds a central b-proteobacterium. The nonmotile chlorobia can perform nitrogen and carbon fixation, using sulfide as electron donors for anoxygenic photosynthesis. The consortium can move due to the flagella present in the central b-protobacterium. Although Chl. chlorochromatii CaD3 is never found as free-living bacteria in nature, previous transcriptomic and proteomic studies have revealed that there are differential transcription patterns between the symbiotic and free-living status of Chl. chlorocromatii CaD3 when grown in laboratory conditions. The differences occur mainly in genes encoding the enzymatic reactions involved in nitrogen and amino acid metabolism. We performed a metabolic reconstruction of Chl. chlorochromatii CaD3 and an in silico analysis of its amino acid metabolism using an elementary flux modes approach (EFM). Our study suggests that in symbiosis, Chl. chlorochromatii CaD3 is under limited nitrogen conditions where the GS/GOGAT (glutamine synthetase/glutamate synthetase) pathway is actively assimilating ammonia obtained via N 2 fixation. In contrast, when free-living, Chl. chlorochromatii CaD3 is in a condition of nitrogen excess and ammonia is assimilated by the alanine dehydrogenase (AlaDH) pathway. We postulate that 'Chlorochromatium aggregatum' originated from a parasitic interaction where the N 2 fixation capacity of the chlorobia would be enhanced by injection of 2-oxoglutarate from the b-proteobacterium via the periplasm. This consortium would have the advantage of motility, which is fundamental to a phototrophic bacterium, and the syntrophy of nitrogen and carbon sources.

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“…Wealso investigated the effect of nitrogen sources in the culture mediumon the formation of the three major ammoniaassimilatory enzymes, glutamate dehydrogenase, glutamine synthetase and glutamate synthase. Glutamate synthase and glutamate dehydrogenase activities were determined by measuring the decrease in absorbance at 340nm of NADPHat 30°C.7) The glutamate synthase assay mixture contained 3.5 mMglutamine, 3.5mM a-ketoglutarate (a-KGA), 0.15mM NADPH, 100mM potassium phosphate buffer (pH 7.0) and the enzymeprotein. Glutamate dehydrogenase was assayed in a mixture containing 50mMNH4C1, 7.0mM a-KGA, 0.15mM NADPH, 100mM potassium phosphate buffer (pH 7.0) and the enzyme protein.…”

Section: Many Investigationsmentioning

confidence: 99%