Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:1.7.1.2 (nitrate reductase)
3,861 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Banding patterns of nitrate reductase (NR), nitrite reductase (NiR), and glutamine synthetase (GS) from leaves of diploid barley (Hordeum vulgare), tetraploid wheat (Triticum durum), hexaploid wheat (Triticum aestivum), and tetraploid wild oats (Avena barbata) were compared following starch gel electrophoresis. Two NR isozymes, which appeared to be under different regulatory control, were observed in each of the three species. The activity of the more slowly migrating nitrate reductase isozyme (NR1) was induced by NO3- in green seedlings and cycloheximide inhibited induction. However, the activity of the faster NR isozyme (NR2) was unaffected by addition of KNO3, and it was not affected by treatments of cycloheximide or chloramphenicol. Only a single isozyme of nitrite reductase was detected in surveys of three tetraploid and 18 hexaploid wheat, and 48 barley accessions; however, three isozymes associated with different ecotypes were detected in the wild oats. Inheritance patterns showed that two of the wild oat isozymes were governed by a single Mendelian locus with two codominant alleles; however, no variation was detected for the third isozyme. Treatment of excised barely and wild oat seedlings with cycloheximide and chloramphenicol showed that induction of NiR activity was greatly inhibited by cycloheximide, but only slightly by chloramphenicol. Only a single GS isozyme was detected in extracts of green leaves of wheat, barley, and wild oat seedlings. No electrophoretic variation was observed within or among any of these three species. Thus, this enzyme appears to be the most structurally conserved of the three enzymes.
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PMID:Inheritance of nitrite reductase and regulation of nitrate reductase, nitrite reductase, and glutamine synthetase isozymes. 1154 65

Recent work in our laboratory indicated that the inhibitory effect of ammonium (NH4+) on assimilatory nitrate reductase (ANR) activity in soil is not due to NH4+ per se but to glutamine formed by microbial assimilation of NH4+. To test this conclusion, we studied the effects of eight analogs of L-glutamine (L-glutamic acid gamma-methyl ester, L-glutamic acid gamma-hydrazide, L-glutamic acid gamma-hydroxamate, L-glutamic acid gamma-ethyl ester, L-glutamic acid dimethyl ester, L-asparagine, L-aspartic acid beta-methyl ester, and L-aspartic acid beta-hydroxamate) and two analogs of ammonium (hydroxylamine and methylamine) on ANR activity in soil slurries. The studies with the L-glutamine analogs showed that all except L-glutamic acid dimethyl ester inhibited ANR activity in soil. The sharp contrast observed between the strong inhibitory effect of L-glutamic acid gamma-methyl ester on ANR activity and the complete lack of an inhibitory effect with the corresponding dimethyl ester suggests that only the free-acid form of glutamine effectively inhibits ANR activity. The studies with hydroxylamine and methylamine showed that both of these ammonium analogs inhibited ANR activity in soil and that this inhibition was dependent upon glutamine synthetase activity. This dependence indicates that inhibition of ANR activity by hydroxylamine and methylamine was due to formation of the glutamine analogs L-glutamic acid gamma-hydroxamate and L-glutamic acid gamma-methylamide, respectively. These observations support the conclusion that the inhibitory effect of NH4+ on ANR activity in soil is due to glutamine formed by microbial assimilation of NH4+.
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PMID:Inhibition of assimilatory nitrate reductase activity in soil by glutamine and ammonium analogs. 1160 3

In Hansenula polymorpha, the expression of the nitrate assimilation metabolism is subjected to re-pression-derepression mechanisms triggered by reduced nitrogen compounds such as ammonium. To further our knowledge on the genetics of these regulatory mechanisms, a screening strategy for the isolation of mutants exhibiting nitrate reductase activities in the presence of reduced nitrogen compounds was set up. This strategy makes use of a nitrate+ methylamine mutant to isolate suppressors of its characteristic phenotype--the inability to grow on a nitrate plus methylamine medium. A total of 21 regulatory mutants were isolated with this strategy and grouped into five complementation classes. One of these mutants harbours the recessive mutation nmr1-1, which determines the derepression of the nitrate assimilation metabolism in media containing nitrate plus a repressing nitrogen source (ammonium, methylamine, glutamate, urea or aspartate). Therefore, nitrate reductase activities are detected in the presence of reduced nitrogen sources, as long as nitrate is also in the medium. Our data indicate that the processes of repression-derepression and induction are controlled by elements which are distinct. Furthermore, they indicate that Nmrlp is involved in repressing circuits which control not only the nitrate-utilisation pathway, but also other pathways which are necessary for the utilisation of nitrogen sources alternative to ammonium. Of considerable interest is the fact that our nmr1-1 mutant is derepressed in glutamate but not in glutamine. Since the phenotype of this mutant seems to exclude a glutamine synthetase defect, we suggest that glutamate (or a derivative of this compound) might be involved in signalling nitrogen metabolite repression in H. polymorpha. Thus, in H. polymorpha, a glutamine-dependent circuit may co-exist with a glutamine-independent circuit.
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PMID:Nitrogen metabolite repression in Hansenda polymorpha: the nmrl-l mutation. 1179 44

Nostoc ANTH is a filamentous, heterocystous cyanobacterium capable of N(2)-fixation in the absence of combined nitrogen. A chlorate-resistant mutant (Clo- R) of Nostoc ANTH was isolated that differentiates heterocysts and fixes N(2) in the presence of nitrate, but not in the presence of nitrite or ammonium. The mutant lacks nitrate uptake and thereby also lacks induction of nitrate reductase activity by nitrate. However, this mutant is able to transport and assimilate nitrite, indicating that there is a transport system for nitrite that is distinct from that for the nitrate. The lack of inhibitory effect of nitrate on N(2)-fixation was owing to lack of nitrate uptake and not to lack of enzymes for its assimilation (nitrate reductase and glutamine synthetase) or the lack of an ammonium transport system for retention of ammonia. The mutant has potential for use as a biofertilizer supplementing chemical nitrate fertilizer in rice fields, without N(2)-fixation being adversely affected.
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PMID:Isolation and characterization of a chlorate-resistant mutant (Clo- R) of the symbiotic cyanobacterium Nostoc ANTH: heterocyst formation and N(2)-fixation in the presence of nitrate, and evidence for separate nitrate and nitrite transport systems. 1207 Jun 86

An important biochemical feature of autotrophs, land plants and algae, is their incorporation of inorganic nitrogen, nitrate and ammonium, into the carbon skeleton. Nitrate and ammonium are converted into glutamine and glutamate to produce organic nitrogen compounds, for example proteins and nucleic acids. Ammonium is not only a preferred nitrogen source but also a key metabolite, situated at the junction between carbon metabolism and nitrogen assimilation, because nitrogen compounds can choose an alternative pathway according to the stages of their growth and environmental conditions. The enzymes involved in the reactions are nitrate reductase (EC 1.6.6.1-2), nitrite reductase (EC 1.7.7.1), glutamine synthetase (EC 6.3.1.2), glutamate synthase (EC 1.4.1.13-14, 1.4.7.1), glutamate dehydrogenase (EC 1.4.1.2-4), aspartate aminotransferase (EC 2.6.1.1), asparagine synthase (EC 6.3.5.4), and phosphoenolpyruvate carboxylase (EC 4.1.1.31). Many of these enzymes exist in multiple forms in different subcellular compartments within different organs and tissues, and play sometimes overlapping and sometimes distinctive roles. Here, we summarize the biochemical characteristics and the physiological roles of these enzymes. We also analyse the molecular evolution of glutamine synthetase, glutamate synthase and glutamate dehydrogenase, and discuss the evolutionary relationships of these three enzymes.
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PMID:Nitrogen-assimilating enzymes in land plants and algae: phylogenic and physiological perspectives. 1220 56

To define further the early, or primary, events that occur in maize (Zea mays) seedlings exposed to NO3-, accumulation of chloroplast glutamine synthetase (GS2; EC 6.3.1.2) and ferredoxin-dependent glutamate synthase (Fd-GOGAT; EC 1.4.7.1), transcripts were examined in roots and leaves. In roots, NO3- treatment caused a rapid (within 30 min), transient, and cycloheximide-independent accumulation of GS2 and Fd-GOGAT transcripts. In addition, 10 [mu]M external NO3- was sufficient to cause transcript accumulation. The induction was NO3- specific, since NH4Cl treatment did not affect mRNA levels. GS2 and Fd-GOGAT mRNA accumulation in roots was similar to that observed for nitrate reductase (NR) mRNA. Therefore, the four genes involved in NO3- assimilation (NR, nitrite reductase, GS2, and Fd-GOGAT) are expressed in the root primary response to NO3-, suggesting that all four genes can respond to the same signal transduction system. In contrast, relatively high levels of GS2 and Fd-GOGAT mRNAs were present in untreated leaf tissue, and NO3- treatment had little or no influence on transcript accumulation. Rapid, transient, and cycloheximide-independent NR mRNA expression was seen in the NO3--treated leaves, demonstrating that NO3- was not limiting. The NO3--independent constitutive expression of GS2 and Fd-GOGAT is likely due to the requirement for reassimilation of photorespiratory NH4+ in these young leaves.
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PMID:Glutamine Synthetase and Ferredoxin-Dependent Glutamate Synthase Expression in the Maize (Zea mays) Root Primary Response to Nitrate (Evidence for an Organ-Specific Response). 1223 79

Physiological alterations and regulation of heterocyst and nitrogenase formation have been studied in Het(-) Fix(-) mutant strain of diazotrophic cyanobacterium Anabaena variabilis. Het(-) Fix(-) mutant strain of A. variabilis has been isolated by N-methyl-N'-nitro-N"-nitrosoguanidine (NTG) mutagenesis and was screened with the penicillin enrichment (500 microg ml(-1)). Growth, heterocyst differentiation, nitrogenase and glutamine synthetase (biosynthetic and transferase), (14)CO(2)-fixation, nitrate reductase (NR), nitrite reductase (NiR), glucose-6-phosphate dehydrogenase (G6PDH), and isocitrate dehydrogenase (IDH) activities, and NO(3)(-), NO(2)(-), and NH(4)(+) uptake and whole cell protein profile in different metabolic conditions were studied in the Het(-) Fix(-) mutant strain taking wild-type A. variabilis as reference. Het(-) Fix(-) mutant strain was incapable of assimilating elemental nitrogen (N(2)) due to its inability to form heterocysts and nitrogenase and this was the reason for its inability to grow in BG-11(0) medium (free from combined nitrogen). In contrast, wild-type strain grew reasonably well in the absence of combined nitrogen sources and also showed heterocyst differentiation (8.5%) and nitrogenase activity (10.8 etamol C(2)H(4) formed microg(-1) Chl a h(-1)) in N(2)-medium. Wild-type strain also exhibited higher NR, NiR, and GS activities compared to its Het(-) Fix(-) mutant strain, which may presumably be due to acquisition of high uptake of NO(3)(-), NO(2)(-), and NH(2)(+). Wild-type strain in contrast to its Het(-) Fix(-) mutant strain also exhibited high level of G6PDH, IDH, and (14)CO(2) fixation activities. Low levels of G6PDH and IDH activities in Het(-) Fix(-) mutant strain further confirmed the lack of heterocyst differentiation and nitrogenase activity in the Het(-) Fix(-) mutant strain.NR, NiR, and GS activities in both the strains were energy-dependent and the energy required is mainly derived from photophosphorylation. Furthermore, it was found that de novo protein synthesis is necessarily required for the activities of NR, NiR, and GS in both wild-type and its Het(-) Fix(-) mutant strain.
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PMID:Physiological alterations and regulation of heterocyst and nitrogenase formation in Het(-) Fix(-) mutant strain of Anabaena variabilis. 1223 60

Nia30(145) transformants with very low nitrate reductase activity provide an in vivo screen to identify processes that are regulated by nitrate. Nia30(145) resembles nitrate-limited wild-type plants with respect to growth rate and protein and amino acid content but accumulates large amounts of nitrate when it is grown on high nitrate. The transcripts for nitrate reductase (NR), nitrite reductase, cytosolic glutamine synthetase, and glutamate synthase increased; NR and nitrite reductase activity increased in leaves and roots; and glutamine synthetase activity increased in roots. The transcripts for phosphoenolpyruvate carboxylase, cytosolic pyruvate kinase, citrate synthase, and NADP-isocitrate dehydrogenase increased; phosphoenolpyruvate carboxylase activity increased; and malate, citrate, isocitrate, and [alpha]-oxoglutarate accumulated in leaves and roots. There was a decrease of the ADP-glucose pyrophosphorylase transcript and activity, and starch decreased in the leaves and roots. After adding 12 mM nitrate to nitrate-limited Nia30(145), the transcripts for NR and phosphoenolpyruvate carboxylase increased, and the transcripts for ADP-glucose pyrophosphorylase decreased within 2 and 4 hr, respectively. Starch was remobilized at almost the same rate as in wild-type plants, even though growth was not stimulated in Nia30(145). It is proposed that nitrate acts as a signal to initiate coordinated changes in carbon and nitrogen metabolism.
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PMID:Nitrate Acts as a Signal to Induce Organic Acid Metabolism and Repress Starch Metabolism in Tobacco. 1223 66

The effect of UV-B radiation on FW, leaf and stem length, photosynthetic O2 evolution, levels of carbohydrates and nitrates, and extractable activities of some of the enzymes involved in C and N metabolism was evaluated in barley (Hordeum vulgare L. cv. Express) seedlings during the 9 days following transfer to an UV-B enriched environment. The results show that under our experimental conditions UV-B radiation scarcely affects the photosynthetic competence of barley leaves, expressed as RuBP carboxylase (EC 4.1.1.39) activity, O2 evolution rate and chlorophyll content. Nevertheless, this treatment induced significant alterations of the enzyme activity of nitrate reductase (EC 1.6.6.1) and glutamine synthetase (EC 6.3.1.2), although only after a few days of treatment. The effects were not confined to the exposed tissue, but were detectable also at the root level. In fact, nitrate reductase decreased in response to UV-B in both leaf and root tissue, whereas glutamine synthetase was affected only in the root. In contrast, nitrate content was not influenced by the treatment, neither in root nor in leaf tissue, whilst leaf sucrose diminished in exposed plants only on the last day of treatment.
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PMID:Carbon and nitrogen metabolism in barley plants exposed to UV-B radiation. 1235 96

In non-photosynthetic, yellow or colourless mutant cells of Chlorella kessleri, grown with nitrate as sole nitrogen source, blue light inhibited the uptake of the amino acids glycine, proline and arginine and of ammonia in growing cells, while it enhanced the uptake of these amino acids in resting cells. On the other hand, in cells grown with ammonia as the only nitrogen source without nitrate reductase activity, blue light did not influence the uptake of amino acids and of ammonia in growing cells, while it enhanced the uptake of amino acids in resting cells. Addition of methionine sulphoximine, a potent inhibitor of glutamine synthetase, to growing cells, resulted in intracellular ammonia-accumulation and inhibition of uptake of glycine and of ammonia. For the colourless mutant, blue light was shown to activate purified nitrate reductase. These results indicate that in the mutant cells of Chlorella examined, uptake of ammonia seems to be influenced by nitrate reductase and the uptake of amino acids was influenced by both nitrate reductase and an unknown blue-light-receptor(s). The uptake of urea in mutant cells is not influenced by the irradiation with blue light. Uptake of glycine was also increased after addition of glucose (hexose) in the dark. Because blue light is known to enhance the breakdown of starch, a reaction producing glucose for oxidative degradation in the algae used, the role of glucose (hexose) in the blue light-affected uptake of amino acids is discussed.
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PMID:Blue-light-control of the uptake of amino acids and of ammonia in Chlorella mutants. 1235 2


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