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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)

A cosmid complementing narG mutants defective in nitrate reductase activity was isolated from a genomic library of Escherichia coli. The restriction map of the insert differed from that of the narGHI operon. The new enzyme, termed NarZ, required molybdenum for activity. The expression of narZ was not affected by the factors controlling narGHI. Insertion mutations indicated that the narZ locus covered about 8 kb of DNA; narZ is located at 32.5 U on the chromosome, in the cotransduction gap near the replication terminus. Southern blot experiments under stringent conditions using narGHI or narZ DNA as probes revealed a large extent of homology, with a small area of very high homology. We propose that narZ and narGHI have descended from a common ancestor by gene duplication.
Mol Microbiol 1987 Sep
PMID:Presence in the 'silent' terminus region of the Escherichia coli K12 chromosome of cryptic gene(s) encoding a new nitrate reductase. 332 96

1. Groups of four conventional (CV) rats ate natural or purified diets either with or without 100 g fat/kg and drank 0.235 M-sodium nitrate. The fats tested were butterfat, coconut oil, olive oil, maize oil and safflower oil. 2. Decreased urinary excretion of N-nitrosoproline (NPRO) was observed in rats fed on fat-supplemented diets compared with those fed on low-fat diets, with butterfat having the greatest effect of the fats tested. 3. Reduced excretion of NPRO was not the result of inhibition of the intragastric N-nitrosation reaction or absorption of nitrosamine from the gastrointestinal tract. 4. The availability of nitrite in aqueous solution was decreased by the fat diets but the effect was similar in all the fats tested. 5. Nitrate reductase activity was present in the forestomach contents of CV rats at pH greater than 4 and was apparently inhibited by feeding a fat diet. No nitrate reductase activity was detected in stomach contents of germ-free rats. 6. Nitrate reductase activity in stomach and small intestinal tissue was not altered by feeding a fat diet. 7. It was concluded that nitrate reductase activity in stomach contents was of microbial origin and the decreased urinary excretion of NPRO on feeding the fat diets was mainly due to the inhibition of nitrate reductase activity in stomach contents.
Br J Nutr 1987 Sep
PMID:Dietary fat and N-nitrosation in the rat. 367 44

Mol- mutants of Klebsiella pneumoniae requiring high levels of molybdate for nitrogenase and nitrate reductase activity were characterized. The effects of mol mutations on nitrogenase activity were very similar to those caused by nifQ mutations. Mol- mutants of K. pneumoniae appear to be equivalent to ChlD- mutants of Escherichia coli.
J Bacteriol 1985 Sep
PMID:Mol- mutants of Klebsiella pneumoniae requiring high levels of molybdate for nitrogenase activity. 389 91

The participation of distinct formate dehydrogenases and cytochrome components in nitrate reduction by Escherichia coli was studied. The formate dehydrogenase activity present in extracts prepared from nitrate-induced cells of strain HfrH was active with various electron acceptors, including methylene blue, phenazine methosulfate, and benzyl viologen. Certain mutants which are unable to reduce nitrate had low or undetectable levels of formate dehydrogenase activity assayed with methylene blue or phenazine methosulfate as electron acceptor. Of nine such mutants, five produced gas when grown anaerobically without nitrate and possessed a benzyl viologen-linked formate dehydrogenase activity, suggesting that distinct formate dehydrogenases participate in the nitrate reductase and formic hydrogenlyase systems. The other four mutants formed little gas when grown anaerobically in the absence of nitrate and lacked the benzyl viologen-linked formate dehydrogenase as well as the methylene blue or phenazine methosulfate-linked activity. The cytochrome b(1) present in nitrate-induced cells was distinguished by its spectral properties and its genetic control from the major cytochrome b(1) components of aerobic cells and of cells grown anaerobically in the absence of nitrate. The nitrate-specific cytochrome b(1) was completely and rapidly reduced by 1 mm formate but was not reduced by 1 mm reduced nicotinamide adenine dinucleotide; ascorbate reduced only part of the cytochrome b(1) which was reduced by formate. When nitrate was added, the formate-reduced cytochrome b(1) was oxidized with biphasic kinetics, but the ascorbate-reduced cytochrome b(1) was oxidized with monophasic kinetics. The inhibitory effects of n-heptyl hydroxyquinoline-N-oxide on the oxidation of cytochrome b(1) by nitrate provided evidence that the nitrate-specific cytochrome is composed of two components which have different redox potentials but identical spectral properties. We conclude from these studies that nitrate reduction in E. coli is mediated by the sequential operation of a specific formate dehydrogenase, two specific cytochrome b(1) components, and nitrate reductase.
J Bacteriol 1969 Sep
PMID:Nitrate reductase complex of Escherichia coli K-12: participation of specific formate dehydrogenase and cytochrome b1 components in nitrate reduction. 490 36

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.
Biochem J 1967 Sep
PMID:Kinetic studies of the induction of nitrate reductase and cytochrome c reductase in the fungus Aspergillus nidulans. 604 55

The concentrations of total extractable N-nitroso compounds, pH, and nitrite levels were measured in fasting gastric juice, which was also cultured for bacteria, from 50 healthy volunteers and 217 patients with common upper gastrointestinal complaints. The concentrations of N-nitroso compounds and pH levels rose significantly with age. Sex and cigarette smoking had no significant effect. There was a positive correlation between pH and N-nitroso concentration, and between pH and an increase in the concentration of nitrites. A significant relation was demonstrated between raised N-nitroso and nitrite levels and growth of nitrate reductase-positive microorganisms. These results demonstrate for the first time in man the interrelations of N-nitrosamine concentration, pH, gastric juice nitrite, and nitrate-reducing bacteria. The findings are considered in relation to the risks of development of gastric cancer in man.
Lancet 1981 Sep 12
PMID:Gastric juice N-nitrosamines in health and gastroduodenal disease. 611 2

The reduced, metal-free pterin of the molybdenum cofactor has been termed molybdopterin. Oxidation of any molybdopterin-containing protein in the presence or absence of iodine yields oxidized molybdopterin derivatives termed Form A and Form B, respectively. Application of these procedures to whole cells and cell extracts has demonstrated the presence of molybdopterin in wild-type Neurospora crassa, and its absence in the cofactor-deficient mutant nit-1. In order to demonstrate that the reconstitution of nitrate reductase activity in nit-1 extracts results from the incorporation of molybdopterin into the apoprotein, active molybdopterin, free of contaminating amino acids or peptides, was isolated from chicken liver sulfite oxidase and used in the reconstitution system. The results show that, during reconstitution, exogenous molybdopterin is specifically incorporated into the nitrate reductase protein, confirming the role of molybdopterin as the organic moiety of the molybdenum cofactor.
Arch Biochem Biophys 1984 Sep
PMID:In vitro reconstitution of nitrate reductase activity of the Neurospora crassa mutant nit-1: specific incorporation of molybdopterin. 623 11

In Aspergillus nidulans, chlorate strongly inhibited net nitrate uptake, a process separate and distinct from, but dependent upon, the nitrate reductase reaction. Uptake was inhibited by uncouplers, indicating that a proton gradient across the plasma membrane is required. Cyanide, azide, and N-ethylmaleimide were also potent inhibitors of uptake, but these compounds also inhibited nitrate reductase. The net uptake kinetics were problematic, presumably due to the presence of more than one uptake system and the dependence on nitrate reduction, but an apparent Km of 200 microM was estimated. In uptake assays, the crnA1 mutation reduced nitrate uptake severalfold in conidiospores and young mycelia but had no effect in older mycelia. Several growth tests also indicate that crnA1 reduces nitrate uptake. crnA expression was subject to control by the positive-acting regulatory gene areA, mediating nitrogen metabolite repression, but was not under the control of the positive-acting regulatory gene nirA, mediating nitrate induction.
J Bacteriol 1983 Sep
PMID:Nitrate uptake in Aspergillus nidulans and involvement of the third gene of the nitrate assimilation gene cluster. 635 Feb 63

The enzyme activity of the rat hindgut microflora maintained in an anaerobic two-stage continuous culture was compared with that of rat cecal contents. A qualitative comparison (API ZYM) showed a high degree of similarity between the two populations. Quantitative determinations showed that azoreductase, beta-glucosidase, nitrate reductase, and nitroreductase activities were comparable, and that beta-glucuronidase activity was very low in the culture. beta-Glucuronidase, beta-glucosidase, and nitrate reductase activities were induced within the culture by their respective substrates. Bile acids influenced microbial activity in vitro, with cholic acid inducing beta-glucosidase, azoreductase, and beta-glucuronidase activities and decreasing nitrate reductase activity. Chenodeoxycholic acid increased beta-glucosidase and beta-glucuronidase activities and decreased azoreductase, nitrate reductase, and nitroreductase activities in vitro. These studies demonstrate that the rat hindgut microflora may be successfully cultured in vitro and suggest control mechanisms that regulate the metabolic activity of these organisms in vivo.
Appl Environ Microbiol 1983 Sep
PMID:Metabolic activity and enzyme induction in rat fecal microflora maintained in continuous culture. 641 66

The molecular basis for the action of two natural inactivator proteins, isolated from rice and corn, on a purified assimilatory nitrate reductase has been examined by several physical techniques. Incubation of purified Chlorella nitrate reductase with either rice inactivator protein or corn inactivator protein results in a loss of NADH:nitrate reductase and the associated partial activity, NADH:cytochrome c reductase, but no loss in nitrate-reducing activity with reduced methyl viologen as the electron donor. The molecular weight of the reduced methyl viologen:nitrate reductase species, determined by sedimentation equilibrium in the Beckman airfuge after complete inactivation with rice inactivator protein or with corn inactivator protein, was 595,000 and 283,000, respectively, compared to a molecular weight of 376,000 for the untreated control determined under the same conditions. Two protein peaks were observed after molecular-sieve chromatography on Sephacryl S-300 of nitrate reductase inactivated by corn inactivator protein. The Stokes radii of these fragments were 68 and 24 A, compared to a value of 81 A for untreated nitrate reductase. The large fragment contained molybdenum and heme but no flavin, and had nitrate-reducing activity with reduced methyl viologen as electron donor. The small fragment contained FAD but had no NADH:cytochrome c reductase or nitrate-reducing activities. Molecular weights determined by sodium dodecyl sulfate-gel electrophoresis were 67,000 and 28,000 for the large and small fragments, respectively, compared to a subunit molecular weight of 99,000 determined for the untreated control. No change in subunit molecular weight of nitrate reductase after inactivation by rice inactivator protein was observed. These results indicate that rice inactivator protein acts by binding to nitrate reductase. The stoichiometry of binding is 1-2 molecules of rice inactivator protein to one tetrameric molecule of nitrate reductase. Corn inactivator protein, in contrast, acts by cleavage of a Mr 30,000 fragment from nitrate reductase which is associated with FAD. The remaining fragment is a tetramer of Mr 70,000 subunits which retains nitrate-reducing activity and contains molybdenum and heme but has no NADH:dehydrogenase activity. The action of rice inactivator protein was partially prevented by NADH and completely prevented by a combination of NADH and cyanide, while the action of corn inactivator protein was not significantly affected by these effectors.
Arch Biochem Biophys 1984 Sep
PMID:Mode of action of natural inactivator proteins from corn and rice on a purified assimilatory nitrate reductase. 654 59


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