scholarly journals Glutamine and asparagine as nitrogen donors for reductant-dependent glutamate synthesis in pea roots

1975 ◽  
Vol 149 (2) ◽  
pp. 403-409 ◽  
Author(s):  
B J Miflin ◽  
P J Lea
Keyword(s):  
Glutamine Synthetase ◽  
Glutamate Synthase ◽  
Crude Extracts ◽  
Pea Root ◽  
Pea Roots ◽  
Nitrogen Donors ◽  
Glutamate Synthesis

Glutamine, in the presence of α-oxoglutarate, stimulates nicotinamide nucleotide oxidation by crude extracts of pea roots and leads to a reductant-dependent formation of glutamate. Commercially available asparagine also stimulates nicotinamide nucleotide oxidation in the presence of α-oxoglutarate, but the reaction causing the stimulation can occur in the absence of a reductant, is inhibited by transaminase inhibitors, and is additive to the glutamine reaction. The asparagine used was found to be contaminated with aspartate. Repurified asparagine, chromatographically free of aspartate, did not stimulate the rate of nicotinamide nucleotide oxidation, and it is probable that the original stimulation was due to aspartate contamination. It is concluded that pea-root glutamine (amide)-α-oxoglutarate aminotransferase (glutamate synthase), in common with the enzyme in leaves, is specific for glutamine as the N donor and α-oxoglutarate as the N acceptor. The significance of the enzyme in conjunction with glutamine synthetase in the assimilation of nitrate by roots is discussed.

Osmoregulation in Rhizobium meliloti: characterization of enzymes involved in glutamate synthesis

1990 ◽  
Vol 36 (7) ◽  
pp. 469-474 ◽  
Author(s):  
Rigoberto Gonzalez-Gonzalez ◽  
James L. Botsford ◽  
Thomas Lewis
Keyword(s):  
Glutamine Synthetase ◽  
Osmotic Stress ◽  
Specific Activity ◽  
Rhizobium Meliloti ◽  
Glutamate Synthase ◽  
The Other ◽  
Glutamine Synthetase Activity ◽  
Biochemical Basis ◽  
Glutamic Dehydrogenase ◽  
Glutamate Synthesis

Rhizobium meliloti, like many bacteria, accumulates elevated levels of glutamate when osmotically stressed. The biochemical basis for this increase in glutamate production was investigated. Enzymes involved in glutamate synthesis, including glutamine synthetase, glutamate synthase, and glutamic dehydrogenase, were characterized in dialyzed crude cell-free extracts. A transaminase activity, which uses branched chain amino acids for the amination of 2-ketoglutaric acid, was also characterized. With the exception of glutamic dehydrogenase, the specific activity of the enzymes did not vary more than 4-fold in response to the available source of nitrogen or supplemental glutamate. Glutamic dehydrogenase activity was 13-fold greater when cells grew with 10 mM [Formula: see text] than when cells grew with 0.5 mM [Formula: see text]. Glutamate synthase was repressed 2-fold when cells grew with supplemental glutamate. Conversely, this enzyme was derepressed 2× when cells grew with 0.5 mM [Formula: see text] or nitrate. Growing cells in minimal defined medium with 400 mM NaCl to cause osmotic stress had little effect on the specific activity of any of the enzymes. The addition of K+ to the reactions stimulated heat-stable glutamine synthetase activity, but inhibited the other enzymes. Glutamate synthase was inhibited to a limited extent by several intermediates in the Krebs' cycle and very severely by glyoxylate. The addition of 10 mM glutamate to the reaction inhibited glutamate synthase 20%, but had no effect on the other enzymes. Key words: enzymes, glutamate synthesis, osmotic stress.

scholarly journals Pathway Choice in Glutamate Synthesis inEscherichia coli

1998 ◽  
Vol 180 (17) ◽  
pp. 4571-4575 ◽  
Author(s):  
Robert B. Helling
Keyword(s):  
Glutamate Synthase ◽  
Substantial Effect ◽  
Ammonium Concentration ◽  
Inescherichia Coli ◽  
Deficient Mutant ◽  
Substrate Availability ◽  
Wild Type ◽  
Limited Growth ◽  
Pathway Choice ◽  
Glutamate Synthesis

ABSTRACT Escherichia coli has two primary pathways for glutamate synthesis. The glutamine synthetase-glutamate synthase (GOGAT) pathway is essential for synthesis at low ammonium concentration and for regulation of the glutamine pool. The glutamate dehydrogenase (GDH) pathway is important during glucose-limited growth. It has been hypothesized that GDH is favored when the organism is stressed for energy, because the enzyme does not use ATP as does the GOGAT pathway. The results of competition experiments between the wild-type and a GDH-deficient mutant during glucose-limited growth in the presence of the nonmetabolizable glucose analog α-methylglucoside were consistent with the hypothesis. Enzyme measurements showed that levels of the enzymes of the glutamate pathways dropped as the organism passed from unrestricted to glucose-restricted growth. However, other conditions influencing pathway choice had no substantial effect on enzyme levels. Therefore, substrate availability and/or modulation of enzyme activity are likely to be major determinants of pathway choice in glutamate synthesis.

Ammonia, glutamine, and asparagine: a carbon–nitrogen interface

1988 ◽  
Vol 66 (10) ◽  
pp. 2103-2109 ◽  
Author(s):  
K. W. Joy
Keyword(s):  
Glutamine Synthetase ◽  
Glutamate Dehydrogenase ◽  
Higher Plants ◽  
Amino Nitrogen ◽  
Glutamate Synthase ◽  
Dinitrogen Fixation ◽  
Similar Function ◽  
Metabolic Processes ◽  
Organic Form ◽  
Primary Input

In plants, the primary input of nitrogen (obtained from the soil or from symbiotic dinitrogen fixation) occurs through the assimilation of ammonia into organic form. Synthesis of glutamine (via glutamine synthetase) is the major, and possibly exclusive, route for this process, and there is little evidence for the participation of glutamate dehydrogenase. A variety of reactions distribute glutamine nitrogen to other compounds, including transfer to amino nitrogen through glutamate synthase. In many plants asparagine is a major recipient of glutamine nitrogen and provides a mobile reservoir for transport to sites of growth; ureides perform a similar function in some legumes. Utilisation of transport forms of nitrogen, and a number of other metabolic processes, involves release of ammonia, which must be reassimilated. In illuminated leaves, there is an extensive flux of ammonia released by the photorespiratory cycle, requiring continuous efficient reassimilation. Aspects of ammonia recycling and related amide metabolism in higher plants are reviewed.

scholarly journals In Vivo Regulation of Glutamine Synthetase Activity in the Marine Chlorophyll b-Containing CyanobacteriumProchlorococcus sp. Strain PCC 9511 (Oxyphotobacteria)

2001 ◽  
Vol 67 (5) ◽  
pp. 2202-2207 ◽  
Author(s):  
Sabah El Alaoui ◽  
Jesús Diez ◽  
Lourdes Humanes ◽  
Fermı́n Toribio ◽  
Frédéric Partensky ◽  
...  
Keyword(s):  
Glutamine Synthetase ◽  
Nitrogen Starvation ◽  
Glutamate Synthase ◽  
Nitrogen Sources ◽  
Synthetase Activity ◽  
Glutamine Synthetase Activity ◽  
Protein Determination ◽  
Physiological Regulation ◽  
Gs Protein

ABSTRACT The physiological regulation of glutamine synthetase (GS; EC6.3.1.2 ) in the axenic Prochlorococcus sp. strain PCC 9511 was studied. GS activity and antigen concentration were measured using the transferase and biosynthetic assays and the electroimmunoassay, respectively. GS activity decreased when cells were subjected to nitrogen starvation or cultured with oxidized nitrogen sources, which proved to be nonusable forProchlorococcus growth. The GS activity in cultures subjected to long-term phosphorus starvation was lower than that in equivalent nitrogen-starved cultures. Azaserine, an inhibitor of glutamate synthase, provoked an increase in enzymatic activity, suggesting that glutamine is not involved in GS regulation. Darkness did not affect GS activity significantly, while the addition of diuron provoked GS inactivation. GS protein determination showed that azaserine induces an increase in the concentration of the enzyme. The unusual responses to darkness and nitrogen starvation could reflect adaptation mechanisms of Prochlorococcus for coping with a light- and nutrient-limited environment.

Influence of nitrogen source and growth status on glutamine synthetase and glutamate synthase activity in Mycobacterium avium

1985 ◽  
Vol 31 (3) ◽  
pp. 211-213
Author(s):  
Charlotte M. McCarthy ◽  
Maria E. Alvarez
Keyword(s):  
Glutamine Synthetase ◽  
Ammonium Chloride ◽  
Mycobacterium Avium ◽  
Cultured Cells ◽  
Specific Activity ◽  
Glutamate Synthase ◽  
Ammonia Concentration ◽  
Apparent Difference ◽  
Growth Status ◽  
Chloride Concentrations

An investigation was made of the activity of glutamine synthetase and glutamate synthase from batch-cultured cells of Mycobacterium avium. The bacteria were grown in medium with ammonium chloride concentrations of 0, 0.1, 0.25, 1, 5, or 25 μmol/mL or with glutamine at 0.1 or 1 μmol/mL. The specific activity of the two enzymes was determined at 0, 22, 45, and 70 h of incubation. Regardless of the ammonia concentration in the medium, glutamate synthase specific activity was two to five times higher in extracts from elongating cells, incubated 22 h, than in those from shortened cells, incubated 45 or 70 h. In contrast, there was no apparent difference in glutamine synthetase specific activity with regard to culture age; however, glutamine synthetase specific activity varied inversely with the concentration of ammonium chloride in the medium. Cells grown in glutamine had high activity of glutamine synthetase.

Exogenous proline application enhances the efficiency of nitrogen fixation and assimilation in chickpea plants exposed to cadmium

2016 ◽  
Author(s):  
Mohammed Nasser Alyemeni ◽  
Qaiser Hayat ◽  
Shamsul Hayat ◽  
Mohammad Faizan ◽  
Ahmad Faraz
Keyword(s):  
Nitrogen Fixation ◽  
Adverse Effects ◽  
Nitrate Reductase ◽  
Glutamine Synthetase ◽  
Glutamate Synthase ◽  
Leaf Nitrogen ◽  
Nitrate Content ◽  
Distilled Water ◽  
Activity Of Enzymes ◽  
Exogenous Proline

Seeds of chickpea were sown in the pots supplemented with 0, 25, 50 or 100 mg of cadmium per kg of soil. At the stage of 30 days after sowing (DAS), the raised plants were sprayed with 20 mM proline except for the control plants which received double distilled water (DDW). The increasing degree of damage caused by the increasing concentration of Cd in soil was partially overcome by proline application. The treatment of 25 mg Cd fed plants with 20 mM proline increased significantly the nodulation parameters, leghemoglobin and carbohydrate content, leaf nitrogen and root nitrate content, activity of enzymes nitrogenase (E.C 1.18.6.1), nitrate reductase (E.C. 1.6.6.1), glutamine synthetase (GS) (E.C 6.3.1.2), glutamate synthase (GOGAT) (E.C 1.4.7.1) and glutamate dehydrogenase (GDH) (E.C 1.4.1.3) over that of the control. The value of these parameters was found to be at par with that of the control in the plants exposed to 50 mg Cd per kg of soil and also treated with 20 mM proline. However, the treatment was not found to be effective in alleviating the adverse effects of 100 mg Cd per kg of soil.

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