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)

The effect of L-methionine-DL-sulfoximine, an inhibitor of glutamine synthetase, on the formation of nitrate reductase in the wild-type strain of Neurospora in the presence of ammonium ions and of glutamine was studied. Under conditions in which glutamine synthetase was inactivated, it was found that only glutamine could repress nitrate reductase. In a mutant of Neurospora, gln-1b, which requires glutamine for growth, only glutamine could repress nitrate reductase. These results suggest a direct role for glutamine as corepressor of nitrate reductase in Neurospora.
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PMID:Repression of nitrate reductase in Neurospora studied by using L-methionine-DL-sulfoximine and glutamine auxotroph gln-1b. 610 50

Growth of Neurospora crassa on media containing NH4+ leads to the repression of a variety of permeases and alternative pathways which would generate NH4+, so called "ammonium repression." The mutant am2 which lacks NADP-GDH is not subject to ammonium repression of nitrate reductase or urea permease, but like the wild type has repressed levels of these systems when grown in the presence of proline, glutamate or glutamine. The glutamine synthetase (GS) mutant gln-1a has derepressed levels of the aforementioned systems unless grown with glutamine. The oligomeric state of GS depends upon the nitrogen sufficiency of the cell, a tetrameric form predominates under conditions of nitrogen limitation and an octameric form under conditions of nitrogen sufficiency. We have found that the tetrameric form GS predominates in the mutants am2 and gln-1a when they are ammonium derepressed. Th mechanism of NH4+ repression in N. crassa is thought to entail a cessation of positive gene action by the product of the nit-2 regulatory gene. We propose that under conditions of NH4+ sufficiency, and hence glutamine sufficiency, the octameric form of GS represses nit-2 gene expression and thereby achieves ammonium repression.
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PMID:The role fo glutamine synthetase and glutamine metabolism in nitrogen metabolite repression, a regulatory phenomenon in the lower eukaryote Neurospora crassa. 610 28

In Neurospora crassa, synthesis of the enzymes of nitrate assimilation, nitrate reductase and nitrite reductase, was repressed by the presence of ammonium, glutamate, or glutamine. This phenomenon was a manifestation of the regulatory process termed nitrogen metabolite repression whereby alternative pathways of nitrogen acquisition are not expressed in cells enjoying nitrogen sufficiency. However, the glutamine synthetase mutant gln-1b had derepressed levels of the nitrate assimilation enzymes. The inability of glutamine to achieve nitrogen metabolite repression in this mutant militated against its potential role as the direct effector of this regulation.
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PMID:Effect of the gln-1b mutation on nitrogen metabolite repression in Neurospora crassa. 610 13

The effect of the nitrogen source on the cellular activity of ferredoxin-nitrate reductase in different cyanobacteria was examined. In the unicellular species Anacystis nidulans, nitrate reductase was repressed in the presence of ammonium but de novo enzyme synthesis took place in media containing either nitrate or not nitrogen source, indicating that nitrate was not required as an obligate inducer. Nitrate reductase in A. nidulans was freed from ammonium repression by L-methionine-D,L-sulfoximine, an irreversible inhibitor of glutamine synthetase. Ammonium-promoted repression appears therefore to be indirect; ammonium has to be metabolized through glutamine synthetase to be effective in the repression of nitrate reductase. Unlike the situation in A. nidulans, nitrate appeared to play an active role in nitrate reductase synthesis in the filamentous nitrogen-fixing strains Anabaena sp. strain 7119 and Nostoc sp. strain 6719, with ammonium acting as an antagonist with regard to nitrate.
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PMID:Regulation of nitrate reductase levels in the cyanobacteria Anacystis nidulans, Anabaena sp. strain 7119, and Nostoc sp. strain 6719. 678 May 11

The mechanism of nitrate uptake for assimilation in procaryotes is not known. We used the radioactive isotope, 13N as NO3-, to study this process in a prevalent soil bacterium, Pseudomonas fluorescens. Cultures grown on ammonium sulfate or ammonium nitrate failed to take up labeled nitrate, indicating ammonium repressed synthesis of the assimilatory enzymes. Cultures grown on nitrite or under ammonium limitation had measurable nitrate reductase activity, indicating that the assimilatory enzymes need not be induced by nitrate. In cultures with an active nitrate reductase, the form of 13N internally was ammonium and amino acids; the amino acid labeling pattern indicated that 13NO3- was assimilated via glutamine synthetase and glutamate synthase. Cultures grown on tungstate to inactivate the reductase concentrated NO3- at least sixfold. Chlorate had no effect on nitrate transport or assimilation, nor on reduction in cell-free extracts. Ammonium inhibited nitrate uptake in cells with and without active nitrate reductases, but had no effect on cell-free nitrate reduction, indicating the site of inhibition was nitrate transport into the cytoplasm. Nitrate assimilation in cells grown on nitrate and nitrate uptake into cells grown with tungstate on nitrite both followed Michaelis-Menten kinetics with similar Km values, 7 muM. Both azide and cyanide inhibited nitrate assimilation. Our findings suggest that Pseudomonas fluorescens can take up nitrate via active transport and that nitrate assimilation is both inhibited and repressed by ammonium.
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PMID:Assimilatory nitrate uptake in Pseudomonas fluorescens studied using nitrogen-13. 678 47

Two nitrogen-regulated genes were found in the genomic DNA region upstream of the nirA operon involved in uptake and utilization of nitrate in Synechococcus sp. strain PCC7942. The two genes (nirB and ntcB) are transcribed divergently from nirA and encode proteins of 349 and 309 amino acid residues, respectively. The levels of nirB and ntcB transcripts were low in cells growing on ammonium and increased upon transfer of ammonium-grown cells to nitrate-containing medium. The deduced NirB protein sequence has no similarities to other known proteins, whereas the deduced NtcB protein sequence is homologous to bacterial transcriptional activators of the LysR family. Defined mutants constructed by interrupting nirB or ntcB with a drug resistance marker grew as fast as the wild-type strain on ammonium but grew slower than the wild-type strain on nitrate or nitrite. The nirB mutant had higher activities of nitrate reductase, glutamine synthetase, and glutamate synthase than the wild-type strain, but its nitrite reductase activity was 40% of the wild-type levels. The mutant excreted nitrite into the medium during growth on nitrate, showing that nitrite reductase limits nitrate assimilation. These findings suggested that nirB is required for expression of maximum nitrite reductase activity. When grown on ammonium, the nirB mutant grew normally but cultures of the ntcB mutant still showed a yellowish-green color typical of nitrogen-limited cells. NtcB seems to regulate utilization of fixed nitrogen by controlling the expression of a certain gene(s) involved in nitrogen metabolism.
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PMID:Identification and characterization of two nitrogen-regulated genes of the cyanobacterium Synechococcus sp. strain PCC7942 required for maximum efficiency of nitrogen assimilation. 781 17

Symbioses between chemoautotrophic bacteria and marine invertebrates living at deep-sea hydrothermal vents and other sulfide-rich environments function autotrophically by oxidizing hydrogen sulfide as an energy source and fixing carbon dioxide into organic compounds. For chemoautotrophy to support growth, these symbioses must be capable of inorganic nitrogen assimilation, a process that is not well understood in these or other aquatic symbioses. Pathways of inorganic nitrogen assimilation were investigated in several of these symbioses: the vent tubeworms Riftia pachyptila and Tevnia jerichonana, the vent bivalves Calyptogena magnifica and Bathymodiolus thermophilus, and the coastal bivalve Solemya velum. Nitrate reductase activity was detected in R. pachyptila, T. jerichonana and B. thermophilus, but not in C. magnifica and S. velum. This is evidence for nitrate utilization, either assimilation or respiration, by some vent species and is consistent with the high levels of nitrate availability at vents. The ammonia assimilation enzymes glutamine synthetase (GS) and glutamate dehydrogenase (GDH) were detected in all symbioses tested, indicating that ammonia resulting from nitrate reduction or from environmental uptake can be incorporated into amino acids. A complicating factor is that GS and GDH are potentially of both host and symbiont origin, making it unclear which partner is involved in assimilation. GS, which is considered to be the primary ammonia-assimilating enzyme of autotrophs, was investigated further. Using a combination of molecular and biochemical approaches, host and symbiont GS were distinguished in the intact association. On the basis of Southern hybridizations, immunoreactivity, subunit size and thermal stability, symbiont GS was found to be a prokaryote GS. Host GS was distinct from prokaryote GS. The activities of host and symbiont GS were separated by anion-exchange chromatography and quantified. Virtually all activity in symbiont-containing tissue was due to symbiont GS in R. pachyptila, C. magnifica and B. thermophilus. In contrast, no symbiont GS activity was detected in the gill of S. velum, the predominant activity in this species appearing to be host GS. These findings suggest that ammonia is primarily assimilated by the symbionts in vent symbioses, whereas in S. velum ammonia is first assimilated by the host. The relationship between varying patterns of GS expression and host-symbiont nutritional exchange is discussed.
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PMID:Pathways of inorganic nitrogen assimilation in chemoautotrophic bacteria-marine invertebrate symbioses: expression of host and symbiont glutamine synthetase 988 41

A cDNA, hvst1, was isolated from Hordeum vulgare by heterologous complementation in Escherichia coli. This cDNA encodes a high-affinity sulfate transporter that is 2442 bp in length and consists of 660 amino acids. Under steady-state conditions of sulfate supply during culture, sulfate influx (measured at 100 microM external sulfate concentration) and hvst1 transcript level were inversely correlated with sulfate concentrations in the culture solution. Glutathione (GSH) concentrations increased as external sulfate was increased from 2.5 to 250 microM. A time-course study, designed to investigate effects of sulfate withdrawal on the abundance of hvst1 transcript, showed a 5-fold increase of the latter within the first two hours. This was followed by a further slight increase during the next 46 h. These changes were accompanied by a parallel increase in sulfate influx and a decrease of root GSH concentrations. When plants that had been deprived of sulfate for 24 h were exposed to L-cysteine (Cys) or GSH for 3 h, GSH was the more effective down-regulator, reducing hvst1 transcript level to below that of unstarved controls. The decrease in transcript abundance induced by sulfate or Cys was partially relieved by the addition of buthionine sulfoximine (BSO), an inhibitor of GSH synthesis. Both hvst1 transcripts and sulfate influx increased as a function of N supply to N-starved plants. Amino oxyacetate acid (AOA), an aminotransferase inhibitor, when supplied with NO3-, increased transcript abundance of hvst1, while tungstate, methionine sulfoximine (MSO) and azaserine (AZA), inhibitors of nitrate reductase, glutamine synthetase and glutamate synthase (GOGAT), respectively, were without effect. AOA decreased root concentrations of aspartate (Asp), Cys and GSH; in contrast, glutamate (Glu) concentrations remained unchanged.
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PMID:Regulation of the hvst1 gene encoding a high-affinity sulfate transporter from Hordeum vulgare. 1048 22

Nitrate assimilation-defective mutants SP7, SP9, and SP17 of the cyanobacterium Anabaena sp. PCC 7120 were isolated by use of transposon mutagenesis and screened on medium containing chlorate. SP7 and SP17 represented nitrate reductase-defective nature, while mutant SP9 appeared to be a regulatory mutant exhibiting pleiotropic behavior. Kinetics of nitrate uptake system exhibited K(s) values of 31-38 &mgr;M for parent, SP7, and SP17 strains; however, mutant SP9 exhibited a high K(s) value of 109.5 &mgr;M. Defective nitrate reductase was apparent in mutant SP7 and SP9, while mutant SP17 exhibited partial defective nature. Methyl viologen-dependent NR activity in parent strain presented a biphasic nature with K(m) values of 0.13 and 2.47 mM, whereas a single K(m) value (2.96 mM) was observed for mutant SP17. Mutant SP9 was also defective in nitrite uptake and reduction. Mutant strains exhibited derepressed nitrogenase activity in the presence of nitrate, while glutamine synthetase activity remained unaltered.http://link.springer-ny. com/link/service/journals/00284/bibs/39n5p237.html</HEA
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PMID:Mutants of the cyanobacterium anabaena sp. PCC 7120 altered in nitrate transport and reduction 1048 30

To investigate the contribution of root cytosolic glutamine synthetase (GS) activity in plant biomass production, two different approaches were conducted using the model legume Lotus japonicus. In the first series of experiments, it was found that overexpressing GS activity in roots of transgenic plants leads to a decrease in plant biomass production. Using (15)N labelling it was shown that this decrease is likely to be due to a lower nitrate uptake accompanied by a redistribution to the shoots of the newly absorbed nitrogen which cannot be reduced due to the lack of nitrate reductase activity in this organ. In the second series of experiments, the relationship between plant growth and root GS activity was analysed using a series of recombinant inbred lines issued from the crossing of two different Lotus ecotypes, Gifu and Funakura. It was confirmed that a negative relationship exists between root GS expression and plant biomass production in both the two parental lines and their progeny. Statistical analysis allowed it to be estimated that at least 13% of plant growth variation can be accounted for by variation in GS activity.
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PMID:Does root glutamine synthetase control plant biomass production in lotus japonicus L.? 1055 Jun 31


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