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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)

The stereospecificity of the hydrogen removal from reduced pyridine nucleotides catalyzed by nitrate reductase (NADH : nitrate oxidoreductase, EC 1.6.6.1, and NAD(P)H : nitrate oxidoreductase, EC 1.6.6.2) was investigated. A high degree of enzyme purification was required to obtain conclusive results. Improvements are described for the purification of nitrate reductase from Chlorella fusca and from spinach (Spinacea oleracea, L.) leaves. The latter enzyme is shown to contain a cytochrome. With highly purified nitrate reductase preparations from Cl. fusca, Neurospora crassa, Rhodotorula glutinis and spinach leaves the stereospecificity of the reaction was determined to be predominantly of the A-type in all cases.
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PMID:The stereospecificity of nitrate reductase for hydrogen removal from reduced pyridine nucleotides. 1 53

Partially purified soluble rat liver guanylate cyclase [GTP pyrophosphate-lyase (cyclizing), EC 4.6.1.2] was activated by superoxide dismutase (superoxide: superoxide oxidoreductase, EC 1.15.1.1). This activation was prevented with KCN or glutathione, inhibitors of superoxide dismutase. Guanylate cyclase preparations formed superoxide ion. Activation by superoxide dismutase was further enhanced by the addition of nitrate reductase. Although guanylate cyclase activity was much greater with Mn2+ than with Mg2+ as sole cation cofactor, activation with superoxide dismutase was not observed when Mn2+ was included in incubations. Catalase also decreased the activation induced with superoxide dismutase. Thus, activation required the formation of both superoxide ion and H2O2 in incubations. Activation of guanylate cyclase could not be achieved by the addition of H2O2 alone. Scavengers of hydroxyl radicals prevented the activation. It is proposed that superoxide ion and hydrogen peroxide can lead to the formation of hydroxyl radicals that activate guanylate cyclase. This mechanism of activation can explain numerous observations of altered guanylate cyclase activity and cyclic GMP accumulation in tissues with oxidizing and reducing agents. This mechanism will also permit physiological regulation of guanylate cyclase and cyclic GMP formation when there is altered redox or free radical formation in tissues in response to hormones, other agents, and processes.
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PMID:Activation of guanylate cyclase by superoxide dismutase and hydroxyl radical: a physiological regulator of guanosine 3',5'-monophosphate formation. 2 77

1. Electron paramagnetic resonance spectra at 8-60 K of NADH-reduced membrane particles prepared from Paracoccus denitrificans grown anaerobically with nitrate as terminal electron acceptor show the presence of iron-sulfur centers 1-4 in the NADH-ubiquinone segment of the respiratory chain. In addition resonance lines at g = 2.058, g = 1.953 and g = 1.88 are detectable in the spectra of succinate-reduced membranes at 15 K, which are attributed to the iron-sulfur-containing nitrate reductase. 2. Sulphate-limited growth under anaerobic conditions does not affect the iron-sulfur pattern of NADH dehydrogenase or nitrate reductase. Furthermore respiratory chain-linked electron transport and its inhibition by rotenone are not influenced. These results contrast those observed for sulphate-limited growth of P. denitrificans under aerobic conditions [Eur. J. Biochem. (1977) 81, 267-275]. 3. Proton translocation studies of whole cells indicate that nitrite increases the proton conductance of the cytoplasmic membrane, resulting in a collapse of the proton gradient across the membrane. Nitrite accumulates under anaerobic growth conditions with nitrate as terminal electron acceptor; the extent of accumulation depends on the specific growth conditions. Thus the low efficiencies of respiratory chain-linked energy conservation observed during nitrate respiration [Arch. Microbiol. (1977) 112, 17-23] can be explained by the uncoupling action of nitrite.
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PMID:Anaerobic respiration and energy conservation in Paracoccus denitrificans. Functioning of iron-sulfur centers and the uncoupling effect of nitrite. 3 82

A ferredoxin was purified from Clostridium perfringens by DEAE-cellulose chromatography and Sephadex G-50 gel filtration. It had absorption maxima at 390 and 280 nm. The molecular weight was estimated to be 6,000 by Sephadex gel filtration and from the results of amino acid analysis. The isoelectric point was 3.0. It contained four atoms of iron, four atoms of labile sulfur, and six cysteine residues. This ferredoxin as well as ferredoxin from C. pasteurianum acted as an electron donor for nitrate reductase from C. perfringens. The ferredoxin could also act as an electron donor for the hydrogenase from C. pasteurianum in hydrogen evolution.
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PMID:Studies on nitrate reductase of Clostridium perfringens. II. Purification and some properties of ferredoxin. 21 25

Cowpea seeds variety Fettriat were planted in Nile silt soil and inoculated with 5 strains of cowpea rhizobia. After 50 and 80 days, the plants were uprooted, analysed for dry weight, total nitrogen, fresh weight of nodules, nitrate reductase activity in the leaves, and nitrate reductase and dehydrogenase activities in the nodule homogenate in the presence or absence of succinate, citrate, and ethyl alcohol. The data were analysed to establish the correlation coefficients between total nitrogen and other characteristics. A significant positive correlation existed between total nitrogen and fresh weight of nodules in both cuts (after 50 and 80 days). The correlation was significant between total nitrogen and dry weight of the plants in the first cut, but was non-significant in the second one. Nitrate reductase activity in leaves and nodule homogenates in the presence of different hydrogen donors were positively correlated in the first cut and negatively correlated in the second one. Nitrate reductase activity in the leaves was much less than that in the nodule homogenates. A negative correlation was noticed between phenol content of the nodules and total nitrogen. In the first cut, while the correlation between total nitrogen and dehydrogenase activity in the presence of citrate or absence of any hydrogen donors was positive, it was negative with ethanol and succinate. In the second cut, however, all the dehydrogenase activities were negatively correlated with total nitrogen.
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PMID:The correlation between the efficiency of rhizobia and nitrate reductase and dehydrogenase activities of cowpea nodules. 72 13

Respiratory nitrate reductase with lactate as a hydrogen donor has been studied in cells and spheroplast preparations of wild type and heme-deficienct mutants of Staphylococcus aureus. The activity is rapidly induced when suspensions of aerobically grown cells are incubated without aeration in a complete medium with nitrate. In ruptured spheroplast preparations, the activity with lactate as the donor is located in the membrane fraction, whereas at least 50% of the activity assayed with reduced benzyl viologen is in the cytoplasm. The reductase is inhibited by azide and cyanide, and the lactate-linked system is also sensitive to oxamate, 2-heptyl-4-hydroxyquinoline-N-oxide, dicoumarol, and p-chloromercuribenzoate. An inactive form of the reductase is apparently made during induction with tungstate; this can be activated by subsequent incubation with molybdate in the presence of chloramphenicol. Nitrate reductase activity with reduced benzyl viologen as the donor is induced in suspensions of heme-deficient mutants in the presence or absence of heme. The proportion of cytoplasmic activity is increased in the absence of heme. The staphylococcal nitrate reductase has many of the characteristics commonly associated with the respiratory enzyme in other organisms, but the apparent predominance of cytoplasmic activity is unusual.
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PMID:Nitrate reductase system in Staphylococcus aureus wild type and mutants. 114 Nov 99

Hydrogenase activity and other hydrogenase-related functions can be restored to hydC mutants by the specific addition of nickel salts to the growth medium. These mutants are defective in all three hydrogenase isoenzymes and the restoration is dependent upon protein synthesis. The cellular nickel content of the mutant when grown in LB medium is less than 1% of that of the parental strain. Partial suppression of the hydrogenase phenotype of hydC mutants occurs when growth takes place in a different medium. This correlates with an increased cellular nickel content. The phenotype of the mutant is also fully suppressed by growth in media of very low magnesium content. Such media facilitate nickel uptake via the magnesium transport system, which leads to the acquisition of a normal cellular nickel content. Mutations in the fnr gene, which encodes a transcriptional regulator for several anaerobically expressed enzymes, abolishes hydC expression and gives rise to a defective hydrogenase phenotype. The hydrogenase phenotype of fnr is closely similar to that of hydC in all respects examined. The hydrogenase activity of fnr strains can be restored by the presence of a functional hydC gene on a multicopy plasmid. The hydrogenase phenotype of fnr strains therefore arises indirectly via suppression of hydC, which leads to a low cellular nickel content. Nickel has no influence on fumarate reductase or nitrate reductase activities in fnr strains. The hydrogen-metabolism phenotype of fnr strains is, therefore, dependent upon their ability to acquire nickel from growth media. It is likely that hydC encodes a specific transport system for nickel.
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PMID:Nickel deficiency gives rise to the defective hydrogenase phenotype of hydC and fnr mutants in Escherichia coli. 269 44

In Escherichia coli, aerobiosis inhibits the synthesis of enzymes for anaerobic respiration (e.g., nitrate reductase and fumarate reductase) and for fermentation (e.g., formate-hydrogen lyase). Anaerobically, nitrate induces nitrate reductase synthesis and inhibits the formation of both fumarate reductase and formate-hydrogen lyase. Previous work has shown that narL+ is required for the effects of nitrate on synthesis of both nitrate reductase and fumarate reductase. Another gene, narK (whose function is unknown), has no observable effect on formation of these enzymes. We report here our studies on the role of nar genes in fumarate reductase and formate-hydrogen lyase gene expression. We observed that insertions in narX (also of unknown function) significantly relieved nitrate inhibition of fumarate reductase gene expression. This phenotype was distinct from that of narL insertions, which abolished this nitrate effect under certain growth conditions. In contrast, insertion mutations in narK and narGHJI (the structural genes for the nitrate reductase enzyme complex) significantly relieved nitrate inhibition of formate-hydrogen lyase gene expression. Insertions in narL had a lesser effect, and insertions in narX had no effect. We conclude that nitrate affects formate-hydrogen lyase synthesis by a pathway distinct from that for nitrate reductase and fumarate reductase.
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PMID:Influence of nar (nitrate reductase) genes on nitrate inhibition of formate-hydrogen lyase and fumarate reductase gene expression in Escherichia coli K-12. 304 31

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

Expression of the tripeptide permease gene tppB is anaerobically induced. This induction is independent of the fnr (oxrA) gene product, which is known to be required for the anaerobic induction of several respiratory enzymes. We isolated, characterized, and mapped mutations in two genes, oxrC and tppR, which prevent the anaerobic induction of tppB expression. Mutations in oxrC were highly pleiotropic, preventing the anaerobic expression of the formate dehydrogenase component of formate hydrogen lyase (fhl), a tripeptidase (pepT), and two of the three known hydrogenase isoenzymes (hydrogenases 1 and 3). On the other hand, expression of nitrate reductase, fumarate reductase, and a number of other fnr (oxrA)-dependent enzymes was not affected by mutations in oxrC. Thus, there appeared to be at least two distinct classes of anaerobically induced genes, those which required fnr for their expression and those which required oxrC. It seems that fnr-dependent enzymes perform primarily respiratory functions, whereas oxrC-dependent enzymes served fermentative or biosynthetic roles. We found the primary defect of oxrC mutants to be a deficiency in phosphoglucose isomerase activity, implying that a product of glycolysis functions as an anaerobic regulatory signal. Mutations in tppR were specific for tppB and did not affect expression of other oxrC-dependent genes. However, tppR did exhibit phenotypes other than the regulation of tppB. Both oxrC and tppR mutants were hypersensitive to the toxic NAD analog 6-aminonicotinic acid. This suggests that oxrC and tppR may play a role in the regulation of NAD biosynthesis or, alternatively, that NAD or a related nucleotide serves as the anaerobic signal for oxrC-dependent enzymes.
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PMID:Two genetically distinct pathways for transcriptional regulation of anaerobic gene expression in Salmonella typhimurium. 353 Nov 76


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