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:1.7.1.1 (nitrate reductase)
3,728 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Seven known genes control Pseudomonas aeruginosa nitrate assimilation. Three of the genes, designated nas, are required for the synthesis of assimilatory nitrate reductase: nasC encodes a structural component of the enzyme; nasA and nasB encode products that participate in the biosynthesis of the molybdenum cofactor of the enzyme. A fourth gene (nis) is required for the synthesis of assimilatory nitrite reductase. The remaining three genes (ntmA, ntmB, and ntmC) control the assimilation of a number of nitrogen sources. The nas genes and two ntm genes have been located on the chromosome and are well separated from the known nar genes which encode synthesis of dissimilatory nitrate reductase. Our data support the previous conclusion that P. aeruginosa has two distinct nitrate reductase systems, one for the assimilation of nitrate and one for its dissimilation.
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PMID:Chromosomal location and function of genes affecting Pseudomonas aeruginosa nitrate assimilation. 642 Mar 93

The in vivo stability of ferredoxin-nitrate reductase from the cyanobacterium Anacystis nidulans under conditions of inhibited protein synthesis has been studied in nitrate-grown cells. A light-promoted rapid decay in cellular nitrate reductase activity took place in the absence of any added nitrogen source, but not in the presence of nitrate, nitrite, or ammonium. The inactivation process seemed to proceed in two sequential steps. The first step required both light and oxygen, and was inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) or, to a lesser extent, by sulfhydryl-containing compounds. The resulting inactive form of nitrate reductase, apparently suffering from an oxidative modification, could be reactivated in vivo either by switching-off the light or by addition of inorganic nitrogenous compounds. Prolonged illumination of the cells in the absence of a nitrogen source led to further modification of the enzyme, which could not be reversed. Stability of the active enzyme appears to be a decisive factor contributing to the determination of the actual level of nitrate reductase in A. nidulans cells.
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PMID:Regulation of the nitrate reductase level in anacystis nidulans: activity decay under nitrogen stress. 643 30

Experiments were performed to determine whether conditions which cause the rapid loss of nitrate reductase activity in Neurospora crassa mycelia were accompanied by the loss of antigenically detectable nitrate reductase protein. When mycelia with nitrate reductase activity were transferred to ammonia media, there was a rapid loss in the reduced nicotinamide adenine dinucleotide-nitrate reductase activity plus the parallel loss of the reduced nicotinamide adenine dinucleotide-diaphorase and the reduced methyl viologen-nitrate reductase activities associated with the nitrate reductase. In addition, there was the loss of cross-reacting material to anti-nitrate reductase antisera that was concomitant with the loss of nitrate reductase activity. When mycelia were exposed to either ammonia plus cycloheximide, nitrate plus cycloheximide, or nitrogen-free media, or to media which lacked an assimilable carbon source, the amount of cross-reacting material declined in concert with the nitrate reductase activity. The mutant nit-6, which lacks nitrite reductase activity, was exposed to ammonia or nitrate plus cycloheximide media. The nitrate reductase and the amount of cross-reacting material declined together as in the wild-type mycelia. We conclude that the loss of nitrate reductase activity was accompanied by the specific loss of this protein and that no pool of inactivated nitrate reductase molecules existed.
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PMID:Repression of nitrate reductase activity and loss of antigenically detectable protein in Neurospora crassa. 644 48

Neurospora crassa nmr-1 mutants, selected on the basis of their sensitivity to chlorate in the presence of glutamine, have elevated levels of the nitrate assimilation enzymes, NADPH-nitrate reductase and NAD(P)H-nitrite reductase. Immunoelectrophoretic determinations show that the higher nitrate reductase activities in nmr-1 mutants are due to greater enzyme concentrations. The half-life of nitrate reductase in these mutants is unaltered. As in wild-type, expression of nitrate assimilation in nmr-1 mutants is dependent on induction by nitrate. Reduced nitrogen metabolites like ammonium and glutamine still repress this expression in nmr-1 mutants, but not as effectively as in wild-type. Enzymatic activity measurements in double mutant strains confirm that the nit regulatory loci, nit-2 and nit-4/5, are epistatic to nmr-1, but nmr-1 is epistatic to nit-3, the nitrate reductase structural gene. The results imply that nmr-1 is involved in post-transcriptional control of nitrate assimilation.
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PMID:The regulation of nitrate assimilation in Neurospora crassa: biochemical analysis of the nmr-1 mutants. 645 34

A biochemical analysis of mutants altered for nitrate assimilation in Neurospora crassa is described. Mutant alleles at each of the nine nit (nitrate-nonutilizing) loci were assayed for nitrite reductase activity, for three partial activities of nitrate reductase, and for nitrite reductase activity. In each case, the enzyme deficiency was consistent with data obtained from growth tests and complementation tests in previous studies. The mutant strains at these nit loci were also examined for altered regulation of enzyme synthesis. Such experiments revealed that mutations which affect the structural integrity of the native nitrate reductase molecule can result in constitutive synthesis of this enzyme protein and of nitrite reductase. These results provide very strong evidence that, as in Aspergillus nidulans, nitrate reductase autogenously regulates the pathway of nitrate assimilation. However, only mutants at the nit-2 locus affect the regulation of this pathway by nitrogen metabolite repression.
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PMID:Biochemical analysis of mutants defective in nitrate assimilation in Neurospora crassa: evidence for autogenous control by nitrate reductase. 646 Jan 56

Cultures of Streptomyces venezuelae grown in a medium containing glucose with mixtures of ammonium and nitrate as the nitrogen source produced chloramphenicol in a distinct idiophase that followed biomass accumulation. Analysis of fermentation broths showed that ammonium and nitrate were taken up consecutively by the organism. Measurements of nitrate reductase in the mycelium established that the enzyme was constitutive and that its specific activity did not increase during the period when ammonium was exhausted from the medium and nitrate was assimilated. The enzyme was neither repressed nor inhibited by ammonium. Production of chloramphenicol was also delayed until ammonium had been consumed and remained slow until subsequent depletion of nitrate. Arylamine synthetase, the initial enzyme in the pathway of antibiotic biosynthesis, showed no marked change in specific activity during utilization of the two nitrogen sources. The result suggests that the mechanism causing preferential utilization of ammonium does not simultaneously control the onset of chloramphenicol biosynthesis.
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PMID:Suppression of nitrate utilization by ammonium and its relationship to chloramphenicol production in Streptomyces venezuelae. 648 3

We show that NADH:nitrate reductase from squash cotyledons can catalyze the reduction of ferric citrate. When nitrate reductase was purified to homogeneity using a two-step affinity chromatography procedure, an NADH:Fe(III)-citrate reductase activity copurified with it and had identical electrophoretic mobility to it. The iron reductase activity was optimum near pH 6.3, had an apparent Km for Fe(III)-citrate of 0.02 mM, and was inhibited by monospecific anti-nitrate reductase rabbit sera. Differential inhibition of the enzyme's activities indicated iron and nitrate were reduced at different sites. In addition to its role in nitrogen assimilation, nitrate reductase catalyzes ferric citrate reduction and could have a role in iron assimilation.
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PMID:Reduction of ferric citrate catalyzed by NADH:nitrate reductase. 668 26

The effect of tungsten on growth and activity of two molybdoenzymes has been studied in a nitrogen-fixing heterocystous cyanobacterium, Anabaena. Sodium tungstate inhibited growth and inactivated nitrogenase and nitrate reductase. The activity of both enzymes was restored by the addition of molybdenum. Tungstate treatment caused increase in heterocyst frequency both in NO3- medium and in medium free of combined nitrogen. These results suggest that tungstate treatment inactivates the molybdoenzymes in this cyanobacterium.
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PMID:Tungsten-induced inactivation of molybdoenzymes in Anabaena. 676 88

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

Six mutant strains (301, 102, 203, 104, 305, and 307) affected in their nitrate assimilation capability and their corresponding parental wild-type strains (6145c and 21gr) from Chlamydomonas reinhardii have been studied on different nitrogen sources with respect to NAD(P)H-nitrate reductase and its associated activities (NAD(P)H-cytochrome c reductase and reduced benzyl viologen-nitrate reductase) and to nitrite reductase activity. The mutant strains lack NAD(P)H-nitrate reductase activity in all the nitrogen sources. Mutants 301, 102, 104, and 307 have only NAD(P)H-cytochrome c reductase activity whereas mutant 305 solely has reduced benzyl viologen-nitrate reductase activity. Both activities are repressible by ammonia but, in contrast to the nitrate reductase complex of wild-type strains, require neither nitrate nor nitrite for their induction. Moreover, the enzyme from mutant 305 is always obtained in active form whereas nitrate reductase from wild-types needs to be reactivated previously with ferricyanide to be fully detected. Wild-type strains and mutants 301, 102, 104, and 307, when properly induced, exhibit an NAD(P)H-cytochrome c reductase distinguishable electrophoretically from constitutive diaphorases as a rapidly migrating band. Nitrite reductase from wild-type and mutant strains is also repressible by ammonia and does not require nitrate or nitrite for its synthesis. These facts are explained in terms of a regulation of nitrate reductase synthesis by the enzyme itself.
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PMID:Regulation of the nitrate-reducing system enzymes in wild-type and mutant strains of Chlamydomonas reinhardii. 681 63


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