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)

Klebsiella aerogenes W70 could grow aerobically with nitrate or nitrite as the sole nitrogen source. The assimilatory nitrate reductase and nitrite reductase responsible for this ability required the presence of either nitrate or nitrite as an inducer, and both enzymes were repressed by ammonia. The repression by ammonia, which required the NTR (nitrogen regulatory) system (A. Macaluso, E. A. Best, and R. A. Bender, J. Bacteriol. 172:7249-7255, 1990), did not act solely at the level of inducer exclusion, since strains in which the expression of assimilatory nitrate reductase and nitrite reductase was was independent of the inducer were also susceptible to repression by ammonia. Insertion mutations in two distinct genes, neither of which affected the NTR system, resulted in the loss of both assimilatory nitrate reductase and nitrite reductase. One of these mutants reverted to the wild type, but the other yielded pseudorevertants at high frequency that were independent of inducer but still responded to ammonia repression.
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PMID:Regulation of assimilatory nitrate reductase formation in Klebsiella aerogenes W70. 225 83

We report the development of a homologous transformation system for Cephalosporium acremonium using the niaD gene of the nitrate assimilation (NA) pathway. Mutants in the NA pathway were selected on the basis of chlorate resistance by conventional means. Screening procedures were developed to differentiate between nitrate reductase apoprotein structural gene mutants (niaD) and molybdenum cofactor gene mutants (cnx) as wt C. acremonium, unlike most filamentous fungi, fails to grow on minimal medium with hypoxanthine as a sole source of nitrogen. Phage clones carrying the niaD gene were isolated from a C. acremonium library constructed in lambda EMBL3 using the A. nidulans niaD gene as a heterologous probe. An 8.6-kb EcoRI fragment was subcloned into pUC18, and designated pSTA700. pSTA700 was able to transform stable niaD mutants to NA at a frequency of up to 40 transformants per microgram DNA. Transformants were easily visible since the background growth was low and no abortives were observed. Gene replacements, single copy homologous integration and complex multiple integrations were observed. The niaD system was used to introduce unselected markers for hygromycin B resistance and benomyl resistance into C. acremonium by cotransformation.
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PMID:Homologous transformation of Cephalosporium acremonium with the nitrate reductase-encoding gene (niaD). 240

The comparative behavior of sulfur (S) and technetium (Tc) in soybean seedlings shows gross subcellular distributions to be similar for these oxyanions. More than 75% of the tissue-deposited Tc remains soluble and extractable. Differences in Tc fixation/incorporation were noted for the nuclear and chloroplast fractions of leaf and root cells. Pulse studies showed that soluble protein and nitrate reductase levels rose in response to Tc accumulation by sink leaves but not source leaves. In vitro assay of chloroplast-based S reduction and incorporation systems showed Tc to be reduced and incorporated into amino nitrogen-containing products. A hypothesis related to the metabolic behavior of Tc in plants is presented.
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PMID:Comparative metabolic behavior and interrelationships of Tc and S in soybean plants. 275 68

Assimilatory nitrate reductase is an inducible, eukaryotic enzyme that responds to a variety of environmental cues. When higher plants and green algae are grown with ammonia as a nitrogen source, low levels of nitrate reductase activity are present. Transfer to nitrate-containing medium is accompanied by substantial increase of nitrate reductase activity. Here it is shown immunologically that, in the green algae Chlorella vulgaris, nitrate reductase protein is over-produced as activity appears during induction. Immunoreactive protein is also found in cells grown on ammonia. Low levels of translatable mRNA for nitrate reductase are present in ammonia-grown cells. These data suggest that: (i) nitrate reductase appearance is controlled primarily on a transcriptional level, but that transcription is not completely halted under repressing conditions; (ii) there is an overproduction of nitrate reductase protein early during the induction period as previously suggested; and (iii) nascent protein, from in vitro translation, is of approximately the same molecular size as the nitrate reductase subunit and therefore little posttranslational modification is necessary to generate the functional enzyme. Insertion of cofactors and assembly are probably the only post-translational events.
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PMID:Induction and synthesis of nitrate reductase in Chlorella vulgaris. 280 25

The nit-2 gene is the major nitrogen-regulatory gene of Neurospora crassa, and under conditions of nitrogen limitations, it turns on the expression of various unlinked structural genes which specify nitrogen-catabolic enzymes. The nit-2 gene was subcloned as a 6-kilobase (kb) DNA fragment from a cosmid that carried approximately a 40-kb N. crassa DNA insert. The nit-2 gene was localized in a DNA segment of approximately 3.5 kb and was shown to correspond to a unique DNA sequence located on linkage group 1. Several N. crassa nit-2 transformants were characterized and were found to possess significantly different levels of the regulated enzyme nitrate reductase. Northern blot analysis of RNA from various strains was carried out to determine whether the nit-2 gene was expressed constitutively or was itself subject to regulation. The results revealed that the nit-2 gene is transcribed to give a single large mRNA of approximately 3.5 kb. Expression of the nit-2 gene is regulated such that its transcript is present at a substantially higher level in cells which are limited for nitrogen than in cells growing under nitrogen-repressed conditions. However, the nit-2 gene is not controlled by autogenous regulation. The nit-2 gene was transcribed only at a low level in nmr-1 and in gln-1b, under both nitrogen-repressed and derepressed conditions, suggesting that these unlinked loci may exert a positive regulatory effect on nit-2.
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PMID:Characterization of nit-2, the major nitrogen regulatory gene of Neurospora crassa. 288 41

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

The NAD(P)H-dependent nitrate reductase system in Clostridium perfringens was reconstituted with rubredoxin (Rd), nitrate reductase (NaR), and an unadsorbed fraction, on a DEAE-cellulose column, of the extract (designated as fraction A), under nitrogen gas. Ferredoxin in place of Rd was not effective as an electron carrier in this reconstituted system. NAD(P)H-dependent nitrate reducing activity was also obtained by replacing fraction A with ferredoxin-NADP+ reductase from spinach. We propose the following scheme for the electron transfer in this NAD(P)H dependent nitrate reduction system. NAD(P)H----NAD(P)H-Rd reductase----Rd----NaR----NO3-.
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PMID:Rubredoxin as an intermediary electron carrier for nitrate reduction by NAD(P)H in Clostridium perfringens. 290 73

Expression of the structural genes of the nitrogen control circuit of Neurospora crassa is regulated by the positive-acting nit-2 control gene and by the negative-acting nmr control gene. Nitrate reductase is expressed in a constitutive fashion in nmr mutant strains, which appear to be largely insensitive to nitrogen catabolite repression. Thus, nmr mutants are sensitive to chlorate in the presence of ammonia or glutamine, whereas the wild type is chlorate resistant under these conditions. A cosmid library was screened for the presence of the nmr+ gene by the sib selection procedure, and a single cosmid was isolated which transforms the nmr mutant to chlorate resistance at a high frequency. A restriction fragment length polymorphism analysis revealed that the cloned DNA segment maps to the precise genomic location of nmr. Northern blot analyses revealed that the nmr gene is itself not regulated but is expressed constitutively to give a single transcript of approximately 1.8 kb.
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PMID:Molecular cloning and characterization of a negative-acting nitrogen regulatory gene of Neurospora crassa. 290 3

The effects of different culture conditions on nitrate reductase activity and nitrate reductase protein from Monoraphidium braunii have been studied, using two different immunological techniques, rocket immunoelectrophoresis and an enzyme-linked immunosorbent assay, to determine nitrate reductase protein. The nitrogen sources ammonium and glutamine repressed nitrate reductase synthesis, while nitrite, alanine, and glutamate acted as derepressors. There was a four- to eightfold increase of nitrate reductase activity and a twofold increase of nitrate reductase protein under conditions of nitrogen starvation versus growth on nitrate. Nitrate reductase synthesis was repressed in darkness. However, when Monoraphidium was grown under heterotrophic conditions with glucose as the carbon and energy source, the synthesis of nitrate reductase was maintained. With ammonium or darkness, changes in nitrate reductase activity correlated fairly well with changes in nitrate reductase protein, indicating that in both cases loss of activity was due to repression and not to inactivation of the enzyme. Experiments using methionine sulfoximine, to inhibit ammonium assimilation, showed that ammonium per se and not a product of its metabolism was the corepressor of the enzyme. The appearance of nitrate reductase activity after transferring the cells to induction media was prevented by cycloheximide and by 6-methylpurine, although in this latter case the effect was observed only in cells preincubated with the inhibitor for 1 h before the induction period.
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PMID:Immunological approach to the regulation of nitrate reductase in Monoraphidium braunii. 291 54

Nitrate reductase catalyzes the initial step in the conversion of nitrate to organic nitrogen and is thought to be repressed by ammonia and induced by nitrate. Induction by nitrate and repression by ammonia were studied by following changes in NADH:nitrate reductase and the associated partial activities NADH:cytochrome c reductase and methylviologenr:nitrate reductase. Immunoreactive protein was assessed by enzyme-linked immunosorbent assay and immunoblotting. Molybdenum cofactor levels were investigated using the nit-1 complementation assay as well as fluorescence of the oxidized cofactor. The results indicate that the NADH:cytochrome c reductase activity is "induced" faster than the nitrate-reducing activity and suggest that incorporation of the molybdo-pterin cofactor may be rate limiting in the expression of activity. Molybdenum cofactor levels are significantly elevated in nitrate-treated cells. Under "repressing" conditions all activities decreased at approximately the same rate. A more rapid conversion of the enzyme to a reversibly inactive form also occurred under these conditions. Changes in immunoreactive protein levels correlated most closely with NADH:cytochrome c reductase activity but appeared to increase faster during induction and decrease slightly slower during repression than the enzyme activities. Removal of exogenous ammonia results in the appearance of nitrate reducing activity, as well as immunoreactive protein (derepression). Studies using protein and RNA synthesis inhibitors indicated that de novo synthesis is required for nitrate reductase induction and were in agreement with the results of the immunoreactive studies.
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PMID:Regulation of Chlorella nitrate reductase: control of enzyme activity and immunoreactive protein levels by ammonia. 291 47


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