Enzymes of ammonia assimilation in Rhizobium leguminosarum bacteroids

1975 ◽  
Vol 21 (7) ◽  
pp. 1009-1012 ◽  
Author(s):  
W. G. W. Kurz ◽  
D. A. Rokosh ◽  
T. A. Larue
Keyword(s):  
Glutamine Synthetase ◽  
Glutamate Dehydrogenase ◽  
Rhizobium Leguminosarum ◽  
Glutamate Synthase ◽  
Dinitrogen Fixation ◽  
Ammonia Assimilation ◽  
Enzymes Of Ammonia Assimilation

The activities of the following enzymes were studied in connection with dinitrogen fixation in pea bacteroids: glutamine synthetase (L-glutamate:ammonia ligase (ADP-forming)) (EC 6.3.1.2) (GS); glutamate dehydrogenase (NADP+) (L-glutamate:NADP+ oxidoreductase (deaminating)) (EC 1.4.1.4) (GDH); glutamate synthase (L-glutamine:2-oxoglutarate aminotransferase (NADPH-oxidizing)) (EC 2.6.1.53) (GOGAT). GS activity was high throughout the growth of the plant and GOGAT activity was always low. It is unlikely that GDH or the GS–GOGAT pathway can account for the incorporation of ammonia from dinitrogen fixation in the pea bacteroid.

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.

Enzymes of Nitrogen Metabolism in Legume Nodules: a Comparative Study

1978 ◽  
Vol 5 (5) ◽  
pp. 553 ◽  
Author(s):  
MJ Boland ◽  
HM Fordyce ◽  
RM Greenwood
Keyword(s):  
Glutamine Synthetase ◽  
Comparative Study ◽  
Glutamate Dehydrogenase ◽  
Nitrogen Metabolism ◽  
Glutamate Synthase ◽  
Ammonia Assimilation ◽  
Legume Species

Levels of activity of glutamine synthetase, glutamate dehydrogenase and NADH-dependent glutamate synthase in nodule cytoplasm extracts of twelve herbaceous legume species have been measured. Nodules of all species contained substantial quantities of glutamine synthetase. Levels of glutamate synthase were found to be between 7 and 100% of those of glutamine synthetase, while levels of glutamate dehydrogenase varied widely between 0.2 and 150% of those of glutamine synthetase. The estimated Km for hydroxylamine of glutamine synthetase was found to vary between 0.02 and 0.5 mM in nine species tested, while that of glutamate dehydrogenase for ammonia varied between 0.03 M and 0.1 M in the four species containing significant levels of that enzyme. It is proposed that the pathway of ammonia assimilation via glutamine synthetase and NADH-dependent glutamate synthase-catalysed reactions is universal in legume nodule metabolism.

scholarly journals The Involvement of Glutamine Synthetase/Glutamate Synthase in Ammonia Assimilation by Aspergillus Nidulans

Microbiology ◽  
1987 ◽  
Vol 133 (5) ◽  
pp. 1235-1242 ◽  
Author(s):  
M. B. Kusnan ◽  
M. G. Berger ◽  
H. P. Fock
Keyword(s):  
Glutamine Synthetase ◽  
Aspergillus Nidulans ◽  
Glutamate Synthase ◽  
Ammonia Assimilation

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.

Plant determined ineffective nodules in alfalfa (Medicago sativa): structural and biochemical comparisons

1983 ◽  
Vol 61 (1) ◽  
pp. 93-106 ◽  
Author(s):  
C. P. Vance ◽  
L. E. B. Johnson
Keyword(s):  
Medicago Sativa ◽  
Phosphoenolpyruvate Carboxylase ◽  
Soluble Protein ◽  
Biochemical Parameters ◽  
Glutamate Synthase ◽  
Host Cells ◽  
Ammonia Assimilation ◽  
Infection Threads ◽  
Medicago Sativa L ◽  
Enzymes Of Ammonia Assimilation

Nodule structure, nodule enzymes of ammonia assimilation, nodule phosphoenolpyruvate carboxylase, nitrogenase-dependent acetylene reduction, and soluble protein were studied in four plant-determined ineffective genotypes and in one effective genotype of alfalfa (Medicago sativa L.) grown in a glasshouse. Ineffective nodules that formed on genotypes MnAg(In) and MnSa(In) were similar to effective nodules in early development. However, these nodules had smaller bacteroids and senesced much more rapidly than effective nodules. In contrast, nodules that formed on ineffective genotypes MnNC-3226(In) and MnNC-3811(In) were tumorlike and had few infection threads and bacteroids, and host cells were filled with starch. Nodules from plant-determined ineffective genotypes had reduced glutamine synthetase, glutamate synthase, phosphoenolpyruvate carboxylase, and nodule soluble protein when compared with effective nodules. There were differences between genotypes for all biochemical parameters assayed.

Sign in / Sign up

Export Citation Format

Share Document