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)

Induced wildtype cells of A. nidulans rapidly lost NADPH--linked nitrate reductase activity when subjected to carbon and or nitrogen starvation. A constitutive mutant at the regulatory gene for nitrate reductase, nir Ac 1, rapidly lost nitrate reductase activity upon carbon starvation. This loss of activity is thought to be due to a decrease in the NADPH concentration in the cells. Cell free extracts from wildtype cells grown in the presence of nitrate, rapidly lost their nitrate reductase activity when incubated at 25 degrees C. NADPH prevented this loss of activity. Wildtype cells grown in the presence of nitrate and urea have a higher initial NADPH:NADP+ ratio and cell free extracts from such cells lost their nitrate reductase activity slower than extracts of cells grown with nitrate alone. The Pentose Phosphate Pathway mutant, pppB-1, had a lower NADPH concentration compared with the wildtype grown under the same conditions and cell free extracts lost their nitrate reductase activity more rapidly than the wildtype. Cell free extracts of nirAc-1 and a non-inducible mutant for nitrate reductase, nirA- -14, upon incubation lost little of their nitrate reductase activity.
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PMID:In vivo and in vitro studies of nitrate reductase regulation in Asperillus nidulans. 1 26

Studies on nitrate reductase (NAD(P)H:nitrate oxidoreductases EC 1.6.6.2) of Cyanidium caldarium revealed that the enzyme is inhibited by excess of electron donor, NADPH, reduced benzylviologen and FMN. Also dithionite, used to reduce benzylviologen and FMN, inactivates nitrate reductase: however, FMN at an optimal concentration and nitrate, added before the dithionite, protect the enzyme against this inactivation. Cyanide, cyanate and carbamyl phosphate inhibit the enzyme competitively with respect to nitrate, and Ki values are reported. Organic mercurials, 0.1 mM, act preferentially on NADPH activity, whereas Ag+ and Hg-2+ at the same concentration inactivate 80--90% of the benzylviologen and FMN activities. ADP is very poor inhibitor. Urea 4 M in 2 h destroys 90% of the NADPH activity and only 30% of the benzylviologen and FMN activities. The apparent Km values for NADPH, benzylviologen, FMN and nitrate have been determined.
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PMID:Electron donors and inhibitors of nitrate reductase from Cyanidium caldarium. 23 76

Mutants of A. nidulans at several loci lack detectable NADPH-nitrate reductase activity. These loci include niaD, the structural gene for the nitrate reductase polypeptide, and five other loci termed cnxABC, E, F, G and H which are presumed to be involved in the formation of a molybdenum-containing component (MCC) necessary for nitrate reductase activity. When forzen mycelia from A. nidulans deletion mutant niaD26 were homogenized in a Ten Broeck homogenizer together with frozen mycelia from either cnxA6, cnxE29, cnsF12, cnxG4 or cnxH3 strains grown on urea + nitrate as the nitrogen source, nitrate reductase activity was detectable in the extract. Similar results were obtained by co-homogenizind niaD mycelia with Neurospora crassa nit-1 mycelia induced on nitrate. Thus, all A. nidulans cnx mutants are similar to the N. crassa nit-1 strain in their capacity to yield NADPH-nitrate reductase in the presence of the presumed MCC. As judged by the amounts of nitrate reductase formed, niaD26 mycelia grown on urea +/- nitrate contained much more available MCC than ammonium-grown mycelia. No NADPH-nitrate reductase activity was found in extracts prepared by co-homogenizing mycelia from all five A. nidulans cnx strains. Wild-type A. nidulans NADPH-nitrate reductase acid dissociated by adjustment to pH 2.0-2.5 AND RE-ADJUSTED TO PH 7 could itself re-assemble to form active nitrate reductase and thus was not a useful source of MCC for these experiments. These results are consistent with the conclusion that the active nitrate reductase complex is composed of polypeptide components which are the niaD gene product, plus the MCC which is formed through the combined action of the cnx gene products. Further, the production of MCC may be regulated in response to the nitrogen nutrition available to the organism.
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PMID:Formation of NADPH-nitrate reductase activity in vitro from Aspergillus nidulans niaD and cnx mutants. 79 78

The nitrate reductase (NR) structural gene (nitA) of Volvox carteri has been cloned and characterized. There is a single copy of this gene in the genome, and RFLP (restriction-fragment length polymorphism) analysis assigns it to the previously defined nitA/chlR locus on linkage group IX, 20-30 cM from the two beta-tubulin-encoding loci. Determination of the 5871-nt sequence of the coding region of genomic clones, and comparisons to a cDNA sequence, revealed ten introns and eleven exons that encode a 864-aa polypeptide. Detailed comparisons with higher-plant and fungal NRs indicate that, whereas the aa sequence is strongly conserved within functional domains for the flavin adenine dinucleotide-, heme- and molybdenum-pterin cofactor-binding sites, substantial differences in the aa sequence occur in the N-terminal end and the two inter-domain regions. Two potential transcription start points 439 and 452 nt upstream from the start codon and a polyadenylation signal 355 nt downstream from the stop codon have been identified by primer-extension analysis and cDNA sequencing, respectively. Accumulation of the nitA transcript is both induced by nitrate and repressed by ammonium and urea: after the organism is transferred from ammonium to nitrate as the nitrogen source, a 3.6-kb NR transcript is readily detectable on Northern blots by 10 min, reaches maximum abundance by 30 min, and then rapidly declines to an intermediate level that is subsequently maintained. Substantial induction by nitrate is observed at the end of the dark portion of the daily light/dark cycle, but the inductive response peaks in the first hour of the light period.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:The nitrate reductase-encoding gene of Volvox carteri: map location, sequence and induction kinetics. 139 26

Molybdenum cofactor (MoCo) of molybdoenzymes is constitutively produced in cells of the green alga Chlamydomonas reinhardtii grown in ammonium media, under which conditions certain molybdoenzymes are not synthesized. In soluble form, MoCo was found to be present in several forms: (i) as a low Mr free species; (ii) bound to a MoCo-carrier protein of about 50 kDa that could release MoCo to directly reconstitute in vitro nitrate reductase activity in the nit-1 mutant of Neurospora crassa, but not to Thiol-Sepharose which, in contrast, bonded free MoCo; and (iii) bound to other proteins, putatively constitutive molybdoenzymes, which only released MoCo after a denaturing treatment. The amount of total MoCo (free, carrier-bound and heat releasable forms) was dependent on the growth phase of cell cultures. Constitutive levels of total MoCo in ammonium-grown cells markedly increased when cells were transferred to media lacking ammonium (nitrate, urea or nitrogen-free media). This increase did not require de novo protein synthesis and was stimulated by light. Levels of both total MoCo and free plus carrier-bound MoCo seemed to be unrelated to either nitrate reductase synthesis or functioning of nit-1 and nit-2 genes responsible for nitrate reductase structure and regulation, respectively. Results suggest that MoCo is continuously synthesized in C. reinhardtii and that its levels are regulated by ammonium in a way independent of nitrate reductase synthesis.
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PMID:Regulation of molybdenum cofactor species in the green alga Chlamydomonas reinhardtii. 182 14

l-Glutamate uptake, thiourea uptake, and methylammonium uptake and the intracellular ammonium concentration were measured in wild-type and mutant cells of Aspergillus nidulans held in various concentrations of ammonium and urea. The levels of l-glutamate uptake, thiourea uptake, nitrate reductase, and hypoxanthine dehydrogenase activity are determined by the extracellular ammonium concentration. The level of methylammonium uptake is determined by the intracellular ammonium concentration. The uptake and enzyme characteristics of the ammonium-derepressed mutants, meaA8, meaB6, DER3, amrA1, xprD1, and gdhA1, are described. The gdhA mutants lack normal nicotinamide adenine dinucleotide phosphate-glutamate dehydrogenase (NADP-GDH) activity and are derepressed with respect to both external and internal ammonium. The other mutant classes are derepressed only with respect to external ammonium. The mutants meaA8, DER3, amrA1, and xprD1 have low levels of one or more of the l-glutamate, thiourea, and methylammonium uptake systems. A model for ammonium regulation in A. nidulans is put forward which suggests: (i) NADP-GDH located in the cell membrane complexes with extracellular ammonium. This first regulatory complex determines the level of l-glutamate uptake, thiourea uptake, nitrate reductase, and xanthine dehydrogenase by repression or inhibition, or both. (ii) NADP-GDH also complexes with intracellular ammonium. This second and different form of regulatory complex determines the level of methylammonium uptake by repression or inhibition, or both.
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PMID:Ammonium regulation in Aspergillus nidulans. 414 65

In an earlier paper (Cove, 1966) it was reported that the kinetics of appearance of nitrate reductase (NADPH-nitrate oxidoreductase, EC 1.6.6.3) on the addition of nitrate to a growing culture of Aspergillus nidulans were different in certain respects from those found for many Escherichia coli enzymes. When urea is used as an initial nitrogen source, a further difference is found: enzyme synthesis is no longer continuous. This interruption of synthesis does not appear to be due to synchronous cell division in the culture, nor to be due to accumulation of ammonia. Fluctuations in the intracellular concentration of nitrate, though appearing to be partly responsible for the discontinuity of enzyme syntheses, cannot account for all the observations. Two related hypotheses are put forward to explain this discontinuity of synthesis; each suggests that nitrate reductase is intimately concerned with its own synthesis. One possibility is that the enzyme when it is not in the form of a complex with nitrate is a co-repressor of its own synthesis, and the other that the enzyme is its own repressor.
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PMID:Kinetic studies of the induction of nitrate reductase and cytochrome c reductase in the fungus Aspergillus nidulans. 604 55

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

The addition of nickel ions restored urease activity in vivo and ability to grow on urea in a mutant strain of Aspergillus nidulans otherwise unable to utilize urea. This train carries a mutation in the ureD locus, one of four loci involved in urea utilization. No other urease-deficient strains tested responded to the presence of nickel ions. The analogous characteristics of the ureD mutant and the nitrate reductase and xanthine dehydrogenase associated cnxE mutants in Aspergillus nidulans are discussed. It is postulated that the ureD locus is in some way involved in the production or incorporation of a nickel cofactor essential for urease activity.
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PMID:Nickel requirement of a urease-deficient mutant in Aspergillus nidulans. 698 44

Nitrate reductase (NAD(P)H:nitrate oxidoreductase, EC 1.6.6.2) of the unicellular alga Cyanidium caldarium can exist in two interconvertible forms; one catalytically active and one inactive. The inactive nitrate reductase can be activated by mild treatment with denaturing agents of protein. By treatment with urea or mersalyl, activation of both the NADPH and benzyl viologen activities can be realized under mild conditions, whereas by treatment with heat, the activation of benzyl viologen activity is concomitant with loss of the NADPH activity. On the other hand, both activities are activated and destroyed concomitantly by ethylene glycol. In the present of FAD, either activation of benzyl viologen activity or loss of NADPH activity upon heating occur only at higher temperatures. The existence of a controlling region in the nitrate reductase molecule is postulated.
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PMID:Active and inactive nitrate reductase. Effects of mild treatment with denaturing agents of protein. 718 70


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