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)

Nicotinamide adenine dinucleotide phosphate (reduced form)-nitrate reductase was freed from ammonium repression in a Neurospora crassa mutant having drastically lowered glutamine synthetase activity, gln-1a. The general phenomenon of nitrogen metabolite repression required glutamine or some aspect of glutamine metabolism.
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PMID:Nitrogen metabolite repression of nitrate reductase in Neurospora crassa: effect of the gln-1a locus. 3 43

The glutamate dehydrogenase and glutamine synthetase activities of an obligate halophyte, Suaeda maritima var. macrocarpa and a glycophyte. Phaseolus vulgaris are compared in function of salinity (increasing concentrations of NaCl) of the culturing solution. In culture, addition of NaCl stimulates glutamine synthetase activity and lowers glutamine dehydrogenase activity in the aerial organs and in the roots of Suaeda as opposed to what is observed in the glycophyte. Hence the obligatory halophily of Suaeda is related to an increase of the glutamine synthetase activity in a sal-trich medium corresponding to the stimulation of nitrate reductase and proteogenesis.
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PMID:[Comparison of glutamate dehydrogenase and glutamine synthetase activities in the roots and aerial organs of an obligate halophyte: Suaeda maritima var. macrocarpa and a glycophyte: Phaseolus vulgaris, grown in presence of different concentration of NaCl]. 4 95

A mutant of Bradyrhizobium (Parasponia) sp. ANU289 affected in the regulation of nitrogen metabolism was isolated. The mutant, designated ANU293, was unable to induce ammonium transport (Amt), nitrate reductase (NR) or glutamine synthetase II (GSII) activities under conditions that induce these activities in the wild-type. However, glutamine synthetase I (GSI), which is expressed constitutively in the wild-type, was present at normal levels in the mutant. The mutant also retained the ability to fix nitrogen in vitro and in planta, although nodule development on siratro (Macroptilium atropurpureum) was retarded. Southern blot analysis showed that ntrC, the product of which is involved in regulation of nitrogen metabolism, is the site of pSUP1021 insertion in ANU293. These results indicate that the transcriptional activator NtrC is required for the expression of Amt, NR and GSII, but not GSI or nitrogenase in Bradyrhizobium (Parasponia) sp. ANU289.
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PMID:Isolation and characterization of a ntrC mutant of Bradyrhizobium (Parasponia) sp. ANU289. 135 84

Twenty-seven mutants that were unable to assimilate nitrate were isolated from Synechococcus sp. strain PCC 7942. In addition to mutants that lacked nitrate reductase or nitrite reductase, seven pleiotropic mutants impaired in both reductases, glutamine synthetase, and methylammonium transport were also isolated. One of the pleiotropic mutants was complemented by transformation with a cosmid gene bank from wild-type strain PCC 7942. Three complementing cosmids were isolated, and a 3.1-kilobase-pair DNA fragment that was still able to complement the mutant was identified. The regulatory gene that was cloned (ntcA) appeared to be required for full expression of proteins subject to ammonium repression in Synechococcus sp.
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PMID:Identification and cloning of a regulatory gene for nitrogen assimilation in the cyanobacterium Synechococcus sp. strain PCC 7942. 196 1

This study presents the effects of Cr, Pb, Ni and Ag on growth, pigments, protein, DNA, RNA, heterocyst frequency, uptake of NH4+ and NO3-, loss of electrolytes (Na+ and K+), nitrate reductase and glutamine synthetase activities of Nostoc muscorum. The statistical tests revealed a direct positive correlation between the metal concentration and inhibition of different processes. Ni was found to be more toxic against growth, pigments and heterocyst differentiation compared to the other metals. Inhibition of pigment showed the following trend: chlorophyll greater than phycocyanin greater than carotenoid. No generalized trend for inhibition of macromolecules was observed. The loss of K+ and Na+ as affected by Cr, Ni and Pb was similar but more pronounced for K+ than Na+. The inhibition of physiological variables depicted the following trend: Na+ loss greater than K+ loss greater than glutamine synthetase greater than NH4+ uptake greater than growth greater than NO3- uptake greater than nitrate reductase greater than heterocyst frequency. This study therefore suggests that loss of electrolytes can be used as a first signal of metal toxicity in cyanobacteria. However, further study is needed to confirm whether the abnormality induced by nickel (branch formation) is a physiological or genetic phenomenon.
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PMID:Effect of four heavy metals on the biology of Nostoc muscorum. 197 95

A positive, genetic selection against the activity of the nitrogen regulatory (NTR) system was used to isolate insertion mutations affecting nitrogen regulation in Klebsiella aerogenes. Two classes of mutation were obtained: those affecting the NTR system itself and leading to the loss of almost all nitrogen regulation, and those affecting the nac locus and leading to a loss of nitrogen regulation of a family of nitrogen-regulated enzymes. The set of these nac-dependent enzymes included histidase, glutamate dehydrogenase, glutamate synthase, proline oxidase, and urease. The enzymes shown to be nac independent included glutamine synthetase, asparaginase, tryptophan permease, nitrate reductase, the product of the nifLA operon, and perhaps nitrite reductase. The expression of the nac gene was itself highly nitrogen regulated, and this regulation was mediated by the NTR system. The loss of nitrogen regulation was found in each of the four insertion mutants studied, showing that loss of nitrogen regulation resulted from the absence of nac function rather than from an altered form of the nac gene product. Thus we propose two classes of nitrogen-regulated operons: in class I, the NTR system directly activates expression of the operon; in class II, the NTR system activates nac expression and the product(s) of the nac locus activates expression of the operon.
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PMID:Role of the nac gene product in the nitrogen regulation of some NTR-regulated operons of Klebsiella aerogenes. 197 23

The toxic effects of chromium and tin salts on growth, 14C uptake, heterocyst differentiation, and nitrate reductase, nitrogenase, and glutamine synthetase activities of Anabaena doliolum and their regulation by pH, salinity, extracellular metabolites (spent), and organic acids have been studied. The toxicity of the test metals was lowered at alkaline pH and increased at acidic pH. NaCl at 20 mM was found to decrease metal toxicity. Extracellular metabolites (spent) in a 1:1 ratio (v/v) with fresh culture medium and organic acids were found to reduce metal toxicity. Among the various organic acids studied, humic acid was the most effective in regulating metal toxicity, apparently due to its multiple binding sites for metal cations. This study demonstrated that environmental factors, such as pH, salinity, extracellular metabolites, and organic acids, can mediate the toxicity of heavy metals to A. doliolum in a laboratory microcosm.
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PMID:Heavy metal toxicity in a N2-fixing cyanobacterium, Anabaena doliolum: regulation of toxicity by certain environmental factors. 212 92

The toxicity of chromium and tin on growth, uptake of NO3- and NH4+, nitrate reductase and glutamine synthetase activity of Anabaena doliolum, and its interaction with bivalent cations, viz. Ca2+, Mg2+, Mn2+, Ni2+, Co2+, and Zn2+, has been studied. Some interacting cations, viz. Ca, Mg, and Mn, substantially antagonized the toxic effects of chromium and tin with reference to growth and nutrient (NO3- and NH4+) uptake in the hierarchical sequence Ca greater than Mg greater than Mn, whereas the sequence of hierarchy was Mn greater than Mg greater than Ca for nitrate reductase and glutamine synthetase activity of A. doliolum. A synergistically inhibitory pattern of interaction was noted for all the parameters, viz. growth, uptake of NO3- and NH4+, nitrate reductase and glutamine synthetase activity of A. doliolum, when Ni, Co, and Zn were used in combination with test metals in the growth medium. These bivalent cations followed the synergistic inhibition sequence Ni greater than Co greater than Zn and potentiated the toxicity of test metals in the N2-fixing cyanobacterium under study.
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PMID:Impact of chromium and tin on a nitrogen-fixing cyanobacterium Anabaena doliolum: interaction with bivalent cations. 256 5

The effects of chromium and tin on survival, growth, carbon fixation, nitrate reduction, ammonia assimilation, and nitrogenase activity of a N2-fixing cyanobacterium. Anabaena doliolum, and their amelioration by synthetic and natural complexans, viz., EDTA, nitrilotriacetic acid (NTA), pyridine dicarboxylic acid (PDA), and citrate, have been studied. Chromium proved to be much more toxic than tin, as it inhibited growth yield (49%), carbon fixation (53%), and nitrate reductase (79%), glutamine synthetase (30%), and nitrogenase activities (77%) at its sublethal concentration, whereas tin induced less inhibition of growth yield (42%), carbon fixation (50%), and nitrate reductase (66%), glutamine synthetase (32.4%), and nitrogenase activities (70%). Despite its inhibitory effects at 10 micrograms ml-1. EDTA supplementation in metal-spiked medium counteracted the toxicity of chromium and tin more significantly than NTA, PDA, and citrate. When supplemented with LD50 of Cr, EDTA protected growth, carbon fixation, NR, GS, and N2ase, respectively, by 32.6, 50.0, 33.3, 17.7, and 65.4%. However, EDTA-induced restoration of the above parameters at a sublethal concentration of tin was only 30.2, 50.0, 28.1, 27.7, and 61.5%, respectively. Although NTA and citrate at 10 micrograms ml-1 each were stimulatory to various processes of test cyanobacterium, they were comparatively less effective than EDTA in the amelioration of metal toxicity. On the basis of these observations, a generalized hierarchical sequence of protective efficiency of synthetic and natural complexing ligands may be given as EDTA greater than NTA greater than citrate greater than PDA. It seems plausible that the toxicity of various heavy metals may be regulated by a large array of organic complexing agents of the aquatic environment because they possess various metal binding sites.
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PMID:Protective effects of certain natural and synthetic complexans on the toxicity of chromium and tin to a N2-fixing cyanobacterium, Anabaena doliolum. 257 94

The nit-3 gene of Neurospora crassa encodes the enzyme nitrate reductase and is regulated by nitrogen catabolite repression and by specific induction with nitrate. The nit-3 gene was isolated from a cosmid-based genomic library by dual selection for benomyl resistance and for the ability to complement a nit-3 mutant strain using the sibling-selection procedure. The nit-3 gene was subcloned as a 3.8-kilobase DNA fragment from a cosmid that carried an approximately 40-kilobase N. crassa DNA insert. A restriction fragment length polymorphism analysis revealed that the cloned segment displayed tight linkage to two linkage-group-4 markers that flank the genomic location of nit-3. RNA gel blot analyses of RNA from wild-type and various mutant strains were carried out to examine the molecular mechanism for regulation of nit-3 gene expression. The nit-3 gene was transcribed to give a large mRNA of approximately 3.4 kilobases, the expected size to encode nitrate reductase. The nit-3 gene was only expressed in wild-type cells subject to simultaneous nitrogen derepression and nitrate induction. A mutant of nit-2, the major nitrogen regulatory gene of Neurospora, did not have detectable levels of nit-3 gene transcripts under the exact conditions in which these transcripts were highly expressed in wild type. Similarly, a mutant of nit-4, which defines a minor positive-acting nitrogen control gene, failed to express detectable levels of the nit-3 transcript. Nitrate reductase gene expression was partially resistant to nitrogen repression in a mutant of the nmr gene, which appears to be a regulatory gene with a direct role in nitrogen catabolite repression. Results are presented that suggest that the enzyme glutamine synthetase does not serve any regulatory role in controlling nitrate reductase gene expression.
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PMID:Molecular cloning and analysis of the regulation of nit-3, the structural gene for nitrate reductase in Neurospora crassa. 289 Nov 38


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