The Aspergillus nidulans gltA gene encoding glutamate synthase is required for ammonium assimilation in the absence of NADP-glutamate dehydrogenase

1999 ◽  
Vol 34 (6) ◽  
pp. 467-471 ◽  
Author(s):  
Maria L. Macheda ◽  
Michael J. Hynes ◽  
M. A. Davis
Keyword(s):  
Glutamate Dehydrogenase ◽  
Aspergillus Nidulans ◽  
Glutamate Synthase ◽  
Ammonium Assimilation ◽  
Gene Encoding ◽  
Glta Gene

Evaluating the Contribution of Glutamate Dehydrogenase and the Glutamate Synthase Cycle to Ammonia Assimilation by Four Ectomycorrhizal Fungal Isolates

1996 ◽  
Vol 23 (2) ◽  
pp. 151 ◽  
Author(s):  
MH Turnbull ◽  
R Goodall ◽  
GR Stewart
Keyword(s):  
Glutamate Dehydrogenase ◽  
Glutamate Synthase ◽  
Ammonium Assimilation ◽  
Major Product ◽  
Ammonia Assimilation ◽  
Gas Chromatography Mass Spectrometry ◽  
Methionine Sulfoximine ◽  
Fungal Isolates ◽  
Glutamine Synthesis ◽  
Fungal Tissue

Combined gas chromatography-mass spectrometry were used to evaluate the contributions of glutamate dehydrogenase (GDH) and the glutamate synthase cycle in 15N-labelled ammonium assimilation by four ectomycorrhizal fungal isolates. In all four species (Elaphomyces, Amanita, Pisolithus and Gautieria), glutamine was the major product accumulated following transfer of 14-day-old nitrogen-limited cultures to fresh medium. Label was rapidly assimilated into fungal tissue, with rates of 733 nmol g-1 FW h-1 in Pisolithus, 972 nmol g-1 FW h-1 in Amanita, 2760 nmol g-1 FW h-1 in Gautieria and 6756 nmol g-1 FW h-1 in Elaphomyces sp in the first 4 h of incubation. Incorporation of [15N]ammonium was sensitive to the inhibitory effects of both methionine sulfoximine (MSX, an inhibitor of glutamine synthetase (GS)) and albizziin (an inhibitor of glutamate synthase (GOGAT)) in three species (Amanita, Gautieria and Pisolithus) and labelling patterns were consistent with the action of the glutamate synthase cycle in ammonium assimilation. In all three species glutamine synthesis was almost totally blocked by MSX and there was no continued incorporation of 15N into glutamate. Elaphomyces displayed high levels of total incorporation of labelled ammonium in mycelium even in the presence of MSX, although incorporation into glutamine was reduced by 88%. This inhibition of GS by MSX, in addition to its partial inhibition by albizziin suggests strongly the action of glutamate synthase cycle in ammonium assimilation. The reduction in label entering glutamate under the influence of albizziin is direct evidence for the inhibition of GOGAT activity. However, MSX treatment had the effect of increasing significantly the quantity of label recovered in both glutamate and alanine. In the absence of GS inhibition there is clearly competition for ammonium which under normal physiological conditions results in assimilation through the glutamate synthase cycle. However, when GS is blocked by MSX label is able to cycle through the GDH pathway. Extra keywords: ectomycorrhiza, ammonium assimilation, glutamate synthase cycle, glutamate dehydrogenase, amino acid metabolism.

scholarly journals The Presence of Glutamate Dehydrogenase Is a Selective Advantage for the Cyanobacterium Synechocystis sp. Strain PCC 6803 under Nonexponential Growth Conditions

1999 ◽  
Vol 181 (3) ◽  
pp. 808-813 ◽  
Author(s):  
S. Chávez ◽  
J. M. Lucena ◽  
J. C. Reyes ◽  
F. J. Florencio ◽  
P. Candau
Keyword(s):  
Glutamate Dehydrogenase ◽  
Glutamate Synthase ◽  
Ammonium Assimilation ◽  
Selective Advantage ◽  
Growth Conditions ◽  
Null Mutant ◽  
Wild Type ◽  
Unicellular Cyanobacterium ◽  
Glutamate Synthesis ◽  
Pcc 6803

ABSTRACT The unicellular cyanobacterium Synechocystis sp. strain PCC 6803 has two putative pathways for ammonium assimilation: the glutamine synthetase-glutamate synthase cycle, which is the main one and is finely regulated by the nitrogen source; and a high NADP-dependent glutamate dehydrogenase activity (NADP-GDH) whose contribution to glutamate synthesis is uncertain. To investigate the role of the latter, we used two engineered mutants, one lacking and another overproducing NADP-GDH. No major disturbances in the regulation of nitrogen-assimilating enzymes or in amino acids pools were detected in the null mutant, but phycobiline content, a sensitive indicator of the nutritional state of cyanobacterial cells, was significantly reduced, indicating that NADP-GDH plays an auxiliary role in ammonium assimilation. This effect was already prominent in the initial phase of growth, although differences in growth rate between the wild type and the mutants were observed at this stage only at low light intensities. However, the null mutant was unable to sustain growth at the late stage of the culture at the point when the wild type showed the maximum NADP-GDH activity, and died faster in ammonium-containing medium. Overexpression of NADP-GDH improved culture proliferation under moderate ammonium concentrations. Competition experiments between the wild type and the null mutant confirmed that the presence of NADP-GDH confers a selective advantage toSynechocystis sp. strain PCC 6803 in late stages of growth.

Isolation and identification of the Aspergillus nidulans gdhA gene encoding NADP-linked glutamate dehydrogenase

1986 ◽  
Vol 10 (10) ◽  
pp. 761-766 ◽  
Author(s):  
Sarah Jane Guff ◽  
Alastair R. Hawkins ◽  
Constantin Drainas ◽  
James R. Kinghorn
Keyword(s):  
Glutamate Dehydrogenase ◽  
Aspergillus Nidulans ◽  
Isolation And Identification ◽  
Gene Encoding

Expression of a ferredoxin-dependent glutamate synthase gene in mesophyll and vascular cells and functions of the enzyme in ammonium assimilation in Nicotiana tabacum (L.)

Planta ◽  
2005 ◽  
Vol 222 (4) ◽  
pp. 667-677 ◽  
Author(s):  
Magali Feraud ◽  
Céline Masclaux-Daubresse ◽  
Sylvie Ferrario-Méry ◽  
Karine Pageau ◽  
Maud Lelandais ◽  
...  
Keyword(s):  
Nicotiana Tabacum ◽  
Glutamate Synthase ◽  
Ammonium Assimilation ◽  
Vascular Cells ◽  
Nicotiana Tabacum L

Properties of NAD-dependent glutamate dehydrogenase from the tylosin producer Streptomyces fradiae

1997 ◽  
Vol 43 (11) ◽  
pp. 1005-1010 ◽  
Author(s):  
Kien Trung Nguyen ◽  
Lieu Thi Nguyen ◽  
Jan Kopecký ◽  
Vladislav Běhal
Keyword(s):  
Key Words ◽  
Glutamate Dehydrogenase ◽  
Reductive Amination ◽  
Divalent Cations ◽  
Ammonium Assimilation ◽  
Alkaline Ph ◽  
Streptomyces Fradiae ◽  
Oxidative Deamination

Glutamate dehydrogenase is an enzyme responsible for ammonium assimilation and glutamate catabolism in organisms. The tylosin producer Streptomyces fradiae possesses both NADP- and NAD-dependent glutamate dehydrogenases. The latter enzyme was purified 498-fold with a 7.5% recovery by a six-step protocol. The enzyme is composed of two subunits, each of Mr 47 000, and could form active aggregates of four or eight subunits. Its activity was inactivated by alkaline pH or temperatures of −20 °C or above 40 °C. Activities assayed in the direction of oxidative deamination and reductive amination were optimal at pH 9.2 and 8.8, respectively, and at temperatures of 30–35 °C. No activity was found when NAD(H) was replaced with NADP(H). The Km values were 32.2 mM for L-glutamate, 0.3 mM for NAD+, 3.4 mM for 2-ketoglutarate, 14.2 mM for NH4+, and 0.05 mM for NADH. Deamination activity was partially inhibited by adenyl nucleotides and several divalent cations; amination activity was not affected by the nucleotides but significantly inhibited by Cu2+ or Ni2+.Key words: Streptomyces fradiae, NAD-dependent glutamate dehydrogenase, purification, properties.

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.

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