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)

Loss-of-function mutations in the regulatory gene areA of Aspergillus nidulans prevent the utilization of a wide variety of nitrogen sources. The phenotypes of nit-2 mutants of Neurospora crassa suggest that this gene may be analogous to the areA gene. Transformation has been used to introduce a plasmid containing the nit-2 gene into A. nidulans. The nit-2 gene of Neurospora complemented mutations in the areA gene, restoring the ability to use a variety of nitrogen sources. This indicated that the activator function of nit-2 and areA gene products was retained across these two fungal species. Southern blot analysis revealed both single-copy and multicopy integrations and, in at least one case, integration appeared to generate a nit-2 mutation. Integration of the transforming plasmid appeared to be by nonhomologous events at a number of different sites in the Aspergillus genome. The transformants were less sensitive to nitrogen-metabolite repression of extracellular protease activity and nitrate reductase (EC 1.6.6.3) than were wild-type A. nidulans. This indicated that nitrogen control was not completely normal in the nit-2 transformants.
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PMID:Complementation of areA- regulatory gene mutations of Aspergillus nidulans by the heterologous regulatory gene nit-2 of Neurospora crassa. 295 60

In Neurospora crassa, the expression of nit-3, the structural gene which encodes nitrate reductase, is highly regulated and requires both nitrate induction and nitrogen catabolite derepression. The major nitrogen regulatory gene, nit-2, acts in a positive fashion to turn on the expression of nit-3 and other nitrogen-related genes during nitrogen derepression. A second regulatory gene, designated nmr, acts in a negative fashion to repress the expression of nitrate reductase and related enzymes, and nmr mutants are partially insensitive to nitrogen repression. Using cloned genes as specific hybridization probes, we demonstrated that nmr does not affect the transcription of nit-2 but does appear to control nit-3 gene expression. Unlike nmr+ expression, nit-3 expression occurred to some degree even under nitrogen repression conditions in nmr mutant cells. In wild-type cells, nitrate reductase gene expression was dependent upon the presence of nitrate as an inducer. In sharp contrast, nit-3 mRNA expression occurred to a full extent in three different nit-3 mutants, even in the complete absence of any added inducer. Similarly, a nit-1 mutant which was devoid of nitrate reductase activity because it lacked an essential molybdenum cofactor expressed nit-3 without a requirement for induction by nitrate. These results suggest that nitrate reductase autogenously regulates its own expression and that this control is exerted at the transcriptional level.
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PMID:Metabolic control and autogenous regulation of nit-3, the nitrate reductase structural gene of Neurospora crassa. 296 90

The nitrate assimilatory pathway in Neurospora crassa is composed of two enzymes, nitrate reductase and nitrite reductase. Both are alpha 2 type homodimers. Enzyme-bound prosthetic groups mediate the electron transfer reactions which reduce inorganic nitrate to an organically utilizable form, ammonium. One, a molybdenum-containing cofactor, is required by nitrate reductase for both enzyme activity and holoenzyme assembly. Three modes of regulation are imposed on the expression of nitrate assimilation, namely: nitrogen metabolite repression, nitrate induction and autogenous regulation by nitrate reductase. In this study, nitrocellulose blots of sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) resolved proteins from crude extracts of the wild type and specific nitrate-nonutilizing (nit) mutants were examined for material cross-reactive with antibodies against nitrate reductase and nitrite reductase. The polyclonal antibody preparations used were rendered monospecific by reverse affinity chromatography. Growth conditions which alter the regulatory response of the organism were selected such that new insight could be made into the complex nature of the regulation imposed on this pathway. The results indicate that although nitrate reductase and nitrite reductase are coordinately expressed under specific nutritional conditions, the enzymes are differentially responsive to the regulatory signals.
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PMID:Nitrate assimilation in Neurospora crassa: enzymatic and immunoblot analysis of wild-type and nit mutant protein products in nitrate-induced and glutamine-repressed cultures. 296 44

Neurospora crassa possesses a set of nitrogen-regulated enzymes whose expression requires a lifting of nitrogen catabolite repression and specific induction. The nit-2 gene is a major regulatory locus which appears to act in a positive way to turn on the expression of these nitrogen-related enzymes whereas the nit-4 gene appears to mediate nitrate induction of nitrate and nitrite reductase. The nit-3 gene specifies nitrate reductase and is subject to control by both nit-2 and nit-4. Many new nit-2, nit-3, and nit-4 mutants were isolated in order to obtain amber nonsense mutations in these loci which were suppressible by the suppressor gene, Ssu-1. A nit-2 nonsense mutant was isolated which has altered regulatory properties for control of nitrate reductase. L-amino acid oxidase, and uricase, and which may encode a truncated regulatory protein. Four nit-3 nonsense mutations were isolated, each of which completely lacks nitrate reductase activity, which is restored to markedly different levels by suppression with Ssu-1. Studies of heat activation and thermal lability of nitrate reductase suggest a qualitative alteration of the enzyme occurs in two of the Ssu-1 nit-3 strains.
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PMID:Amber nonsense mutations in regulatory and structural genes of the nitrogen control circuit of Neurospora crassa. 296 95

Xanthine dehydrogenase (XDH) is the initial enzyme in the purine catabolic pathway of N. crassa. Secondary nitrogen sources such as purines are metabolized when preferred sources of reduced nitrogen (ammonium or glutamine) are unavailable. XDH synthesis is regulated by glutamine repression and uric acid induction. The nit-2 locus is believed to encode a trans-acting positive regulator essential for the expression of genes encoding enzymes involved in secondary pathways of nitrogen acquisition, such as XDH and nitrate reductase. However, immunoblot analyses and enzyme assays reveal that XDH protein is synthesized and XDH activity is expressed in nit-2 mutants. Nevertheless, XDH responds to nitrogen metabolite repression. The generality that nit-2 is an obligate control element in nitrogen metabolite repression is questioned. Additionally, mutants defective in XDH activity, namely, xdh-1 and the molybdenum cofactor mutants nit-1, -7, -8 and -9, are observed to grow on xanthine but not hypoxanthine.
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PMID:Xanthine dehydrogenase expression in Neurospora crassa does not require a functional nit-2 regulatory gene. 296 94

The nitrogenase activity, nitrate reductase activity and oxygen uptake as well as the hydrogen incorporation and ATP content were examined in the root nodules and bacteroids, respectively, formed by Rhizobium leguminosarum strains 128C53 (hydrogenase positive) and 300 (hydrogenase negative) in symbiosis with Pisum sativum plants grown in the presence of 2 mM KNO3. The strain 128C53 showed the greatest values for all parameters analyzed, except for the nitrate reductase activity, which was higher for the strain 300. Similarly, nodule nitrate reductase activity in strain 300 was greater than that in strain 128C53 when plants grew in the absence of combined nitrogen. In general, the highest values were obtained when determinations were made after 7 hours of plant illumination. However, the hydrogenase activity of strain 128C53 and the nitrate reductase activities of both strains increased with the light period, reaching a maximum after 14 hours of illumination. These results suggest that the benefits derived from the superior symbiotic properties and from the presence of hydrogenase activity in strain 128C53 could be counteracted by the higher rates of the nodule nitrate reductase activity in strain 300.
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PMID:[Nitrogenase, hydrogenase and nitrate reductase activities, oxygen consumption, and ATP content in nodules formed by strains of Rhizobium leguminosarum 128C53 and 300 in symbiosis with pea plants]. 307 42

The main nitrogen source for most higher plants is soil nitrate. Prior to its incorporation into amino acids, plants reduce nitrate to ammonia in two enzymatic steps. Nitrate is reduced by nitrate reductase to nitrite, which is further reduced to ammonia by nitrite reductase. In this paper, the complete primary sequence of the precursor protein for spinach nitrite reductase has been deduced from cloned cDNAs. The cDNA clones were isolated from a nitrate-induced cDNA library in two ways: through the use of oligonucleotide probes based on partial amino acid sequences of nitrite reductase and through the use of antibodies raised against purified nitrite reductase. The precursor protein for nitrite reductase is 594 amino acids long and has a 32 amino acid extension at the N-terminal end of the mature protein. These 32 amino acids most likely serve as a transit peptide involved in directing this nuclear-encoded protein into the chloroplast. The cDNA hybridizes to a 2.3 kb RNA whose steady-state level is markedly increased upon induction with nitrate.
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PMID:Isolation of cDNA clones coding for spinach nitrite reductase: complete sequence and nitrate induction. 316 66

The inhibitor of mRNA synthesis, 6-methylpurine, inhibited nitrate reductase derepression in either ammonium-grown or methylammonium-treated wild-type cells of Chlamydomonas reinhardtii, but not in nitrogen-starved cells. In contrast, 6-methylpurine did not inhibit nitrate reductase synthesis in the methylammonium-resistant mutant 2170 (ma-1) either grown on ammonium, treated with methylammonium or nitrogen starved, but did inhibit the continuous synthesis of nitrate reductase, which required the presence of nitrate in the media. In both wild-type and mutant 2170 grown on ammonium and transferred to nitrate media, cycloheximide immediately prevented nitrate reductase derepression when added either at the beginning or at different times of induction treatment. Unlike wild-type cells, mutant 2170 was able to take up either nitrate or nitrite simultaneously with ammonium in whose presence nitrate and nitrite reductases were synthesized. However, synthesis of nitrate reductase was progressively inhibited in the mutant cells when the intracellular ammonium levels were raised as a result of an increase in either the external pH or the extracellular ammonium concentrations. The results rule out the existence of maturase-like proteins in Chlamydomonas and indicate that ammonium has a double effect on the regulation of nitrate reductase synthesis: (a) it prevents nitrate reductase mRNA production; and (b) it controls negatively the expression of this mRNA.
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PMID:Regulation by ammonium of nitrate and nitrite assimilation in Chlamydomonas reinhardtii. 319 Nov 35

Bradyrhizobium japonicum JH mutants deficient in molybdenum metabolism into the enzymes nitrogenase and nitrate reductase were isolated by using the vector pSUP1011, which carries transposon Tn5 (streptomycin and kanamycin resistance). Mutants in Mo metabolism were obtained at a frequency of 3.6 X 10(-3) (per Kan Strr colony). The mutants were detected by their poor ability to grow in nitrate-containing medium without added Mo. One of the mutant types required 10(5) times more molybdate than the wild type to obtain maximal nitrogen fixation activity. Double-reciprocal plots of Mo uptake versus concentration indicated that the wild-type strain had a high- and a lower-affinity component for Mo binding. Mutant strains JH-90 and JH-119 lacked the high-affinity Mo uptake component and were also clearly deficient in Mo accumulation into a nonexchangeable form. Nitrogenase activity as well as Mo uptake ability could be restored in strains JH-90 and JH-119 by the addition of the sterile supernatant fraction of the wild type. Therefore, mutant strains JH-90 and JH-119 appeared to be deficient in an extracellular Mo-binding factor produced by the wild type. Mutant strains JH-14 and JH-143 had Mo uptake kinetics like those of the wild type (both high- and low-affinity binding for Mo) and appeared to be deficient in intracellular Mo metabolism processes. The addition of the wild-type supernatant did not restore Mo uptake or nitrogenase activity in these strains.
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PMID:Bradyrhizobium japonicum mutants defective in nitrogen fixation and molybdenum metabolism. 347 63

In vivo labelling and in vitro translation studies were used to study the regulation of the synthesis of nitrate reductase in the yeast Candida nitratophila. These studies showed that synthesis of the enzyme subunit took place when ammonium-grown cells were nitrogen-starved and this was stimulated by subsequent addition of nitrate. Ammonium-grown cultures did not contain mRNA that could be translated into the nitrate reductase subunit in an in vitro system. Nitrate reductase mRNA could be extracted from nitrogen-starved and nitrate cultures. Synthesis of the enzyme is apparently controlled at the level of transcription in this yeast.
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PMID:Evidence for the transcriptional control of nitrate reductase in Candida nitratophila from in vitro translation studies. 356 70


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