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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)

Molybdenum cofactor (mocofactor) is extracted efficiently, free of impurities and in high concentrations, by acid treatment of xanthine oxidase and subsequent incubation of the precipitate with phosphate buffer containing EDTA, molybdate and oxygen. It is suggested that cofactor is bound to the enzyme via hydrophobic forces as well as via an oxygen-sensitive mechanism. Upon extraction, the capability to complement the apo nitrate reductase of Neurospora crassa nit-1 can be conserved only in the total absence of oxygen. Cysteine and glutathione were shown to protect efficiently free mocofactor from oxidation. Two species of active mocofactor, probably a molybdoform and a demolybdoform, could be separated by means of reversed-phase HPLC with a mobile phase of 5 mM sodium citrate at a pH of 6.5. The mode of interaction between either of these species with thiol reagents is discussed.
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PMID:Extraction and purification of molybdenum cofactor from milk xanthine oxidase. 369 96

During oxidation of nitrite, cells of Nitrobacter winogradskyi are shown to catalyze the active exchange of oxygen atoms between exogenous nitrate molecules (production of 15N16/18O3- during incubation of 14N16/18O3-, 15N16O3-, and 15N16O2- in H216O). Little, if any, exchange of oxygens between nitrate and water also occurs (production of 15N16/18O3- during incubation of 15N16O3- and 14N16O2- in H218O). 15N species of nitrate were assayed by 18O-isotope shift in 15N NMR. Taking into account the O-exchange reactions which occur during nitrite oxidation, H2O is seen to be the source of O in nitrate produced by oxidation of nitrite by N. winogradskyi. The data do not establish whether the nitrate-nitrate O exchange is catalyzed by nitrite oxidase (H2O + HNO2----HNO3 + 2H+ + 2e-) or nitrate reductase (HNO3 + 2H+ + 2e-----HNO2 + H2O) or both enzymes in consort. The nitrate-nitrate exchange reaction suggests the existence of an oxygen derivative of a H2O-utilizing oxidoreductase.
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PMID:Oxygen exchange between nitrate molecules during nitrite oxidation by Nitrobacter. 373 17

Nitrobacter agilis, which contains a very active nitrite dehydrogenase, was studied in vivo under anaerobic conditions by the 15N NMR technique. When incubated with equimolar 15NO3- and unlabeled nitrite (or 15NO2- and unlabeled nitrate) the bacterium catalyzed an isotope exchange reaction at rates about 10% those observed in the nitrite oxidase assay. When incubated with 18O-labeled 15NO2- and 18O-labeled 15NO3-, the 18O was observed to exchange at similar rates from both species into water. Finally, when incubated with equimolar [18O]nitrate and 15NO2-, intermolecular 18O transfer was observed to result in formation of double labeled nitrate and nitrite at similar rates. 18O was transferred from nitrate to a 15N species or to water at approximately equal rates under the conditions of the experiments. It is argued that the enzyme responsible for these exchange reactions is nitrite dehydrogenase and not nitrate reductase. This work and the related experiments of DiSpirito and Hooper (DiSpirito, A.A., and Hooper, A.B. (1986) J. Biol. Chem. 261, 10534-10537) represent the first demonstrations of intermolecular oxygen atom transfer among oxotransferases. Mechanistic implications are discussed.
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PMID:Catalysis of intermolecular oxygen atom transfer by nitrite dehydrogenase of Nitrobacter agilis. 373 18

Formation of nitrate reductase (NaR) and nitrous oxide reductase (N2OR) by a Pseudomonas sp. G59 did not occur in aerobic or anaerobic conditions, but was observed in a microaerobic incubation in which an anaerobically grown culture was agitated in a sealed vessel initially containing 20 kPa oxygen in the headspace. During the microaerobic incubation, the oxygen concentration in the headspace decreased and dissolved oxygen reached 0.1-0.2 kPa. NaR activity was detected immediately and N2OR activity after 3 h of incubation irrespective of the presence or absence of NO3- or N2O. In the presence of NO3-, NO2- was accumulated as a major product, but N2O was observed in low concentrations only after N2OR appeared. After microaerobic incubation for 3 h, N2OR formation continued even anaerobically in an atmosphere of N2O. In contrast, Escherichia coli formed NaR not only microaerobically but also anaerobically. However, NaR formation by E. coli was inhibited by sodium fluoride under anaerobic, but not under microaerobic conditions. The Pseudomonas culture did not possess fermentative activity. It is suggested that the dependence on microaerobiosis for the formation of these reductases by the Pseudomonas culture was due to an inability to produce energy anaerobically until these anaerobic respiratory enzymes were formed.
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PMID:Temporary low oxygen conditions for the formation of nitrate reductase and nitrous oxide reductase by denitrifying Pseudomonas sp. G59. 374 33

We report some properties of Protein PA which has been isolated from the soluble fraction of a chlB mutant after anaerobic growth in the presence of KNO3. This protein has been identified by its capacity to reactivate nitrate reductase present in the soluble fraction of a chlA mutant by the complementation process. The presence of active Protein PA in the chlB mutant is independent of the presence of oxygen or of nitrate during growth. In contrast, the addition of sodium tungstate to the growth medium leads to the formation of inactive Protein PA which is not able to activate nitrate reductase in the chlA-soluble extract by complementation. Inactive Protein PA has been quantitated immunologically. The partial purification of Protein PA has been achieved from various chlorate-resistant mutants (chlA-chlG). The establishment of particular complementation systems comprising the soluble extracts of chlA or chlB mutants and partially purified Protein PA from soluble fractions of different chlorate-resistant mutants, has allowed the quantitative estimation of this protein. The analysis by 'rocket immunoelectrophoresis' using an antiserum specific for Protein PA has shown that inactive Protein PA is present in approximately equivalent amounts in the chlA, chlE, chlG and chlD mutants.
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PMID:Identification in various chlorate-resistant mutants of a protein involved in the activation of nitrate reductase in the soluble fraction of a chlA mutant of Escherichia coli K-12. 388 12

Downey, R. J. (University of Notre Dame, Notre Dame, Ind.). Nitrate reductase and respiratory adaptation in Bacillus stearothermophilus. J. Bacteriol. 91:634-641. 1966.-Bacillus stearothermophilus 2184 required nitrate to grow in the absence of oxygen. Like many facultative microorganisms, the growth obtained anaerobically was considerably less than that obtained aerobically, even though the dissimilatory reduction of nitrate is, in effect, anaerobic respiration. The ability to reduce nitrate depended on the induction of nitrate reductase. Although oxygen at low levels did not retard induction of the enzyme, enzyme synthesis was considerably lessened by aeration. A semisynthetic medium containing nitrate supported aerobic growth of the thermophile but did not support anaerobic growth. The adaptation to nitrate resulted in a decrease in the level of cytochrome oxidase normally present in aerobically grown cells. Although the aerobic oxidation of succinate by the respiratory enzymes from aerobically grown cells was inhibited by 2-N-heptyl-4-hydroxyquinoline-N-oxide, the anaerobic oxidation of succinate by nitrate in a similar preparation from nitrate-adapted cells was not. The nitrate reductase in the bacillus was strongly inhibited by cyanide and azide but not by carbon monoxide. The nitrate reductase catalyzed the anaerobic oxidation of reduced nicotinamide adenine dinucleotide, and appeared to transfer electrons from cytochrome b(1) to nitrate. Cytochrome c(1) did not appear to be involved in the transfer.
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PMID:Nitrate reductase and respiratory adaptation in Bacillus stearothermophilus. 428 85

The role of selenium and molybdenum in the metabolism of Escherichia coli was explored by growing cells in a simple salts medium and examining the metabolic consequences of altering the concentration of molybdenum and selenium compounds in the medium. The addition of tungstate increased the molybdate deficiency of this medium, as reflected by lowered levels of enzyme systems previously recognized to require compounds of molybdenum and selenium for their formation [formate-dependent oxygen reduction, formate dehydrogenase (FDH) (EC 1.2.2.1), and nitrate reductase (EC 1.9.6.1)]. The requirement for selenium and molybdenum appears to be unique to the enzymes of formate and nitrate metabolism since molybdate- and selenite-deficient medium had no effect on the level of several dehydrogenase and oxidase systems, for which the electron donors were reduced nicotinamide adenine dinucleotide, succinate, d- or l-lactate, and glycerol. In addition, no effect was observed on the growth rate or cell yield with any carbon source tested (glucose, glycerol, dl-lactate, acetate, succinate, and l-malate) when the medium was deficient in molybdenum and selenium. dl-Selenocystine was about as effective as selenite in stimulating the formation of formate dehydrogenase, whereas dl-selenomethionine was only 1% as effective. In aerobic cells, an amount of FDH was formed such that 3,200 or 3,800 moles of formate were oxidized per min per mole of added selenium (added as dl-selenocystine or selenite, respectively).
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PMID:Effects of molybdate, tungstate, and selenium compounds on formate dehydrogenase and other enzyme systems in Escherichia coli. 455 2

The influence of growth conditions on assimilatory and respiratory nitrate reduction in Aerobacter aerogenes was studied. The level of nitrate reductase activity in cells, growing in minimal medium with nitrate as the sole nitrogen source, was much lower under aerobic than anaerobic conditions. Further, the enzyme of the aerobic cultures was very sensitive to sonic disintegration, as distinct from the enzyme of anaerobic cultures. When a culture of A. aerogenes was shifted from anaerobic growth in minimal medium with nitrate and NH(4) (+) to aerobiosis in the same medium, but without NH(4) (+), the production of nitrite stopped instantaneously and the total activity of nitrate reductase decreased sharply. Moreover, there was a lag in growth of about 3 hr after such a shift. After resumption of growth, the total enzymatic activity increased again slowly and simultaneously became gradually sensitive to sonic disintegration. These findings show that oxygen inactivates the anaerobic nitrate reductase and represses its further formation; only after a de novo synthesis of nitrate reductase with an assimilatory function will growth be resumed. The enzyme in aerobic cultures was not significantly inactivated by air, only by pure oxygen. The formation of the assimilatory enzyme complex was repressed, however, by NH(4) (+), under both aerobic and anaerobic conditions. The results indicate that the formation of the assimilatory enzyme complex and that of the respiratory enzyme complex are regulated differently. We suggest that both complexes have a different composition, but that the nitrate reductase in both cases is the same protein.
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PMID:Regulation of nitrate assimilation and nitrate respiration in Aerobacter aerogenes. 572 95

A denitrifying mutant of Bacillus stearothermophilus NCA 2184, strain 2184-D, was used to explore the development of nitrate respiration in relation to oxygen respiration. Aerobically grown wild-type cultures could acquire the ability to use nitrate as a result of selection of nitrate-respiring mutants by the presence of nitrate and a reduced oxygen tension. Fluctuation analysis has revealed that the frequency of occurrence of the nitrate-respiring mutant is about 7.5 x 10(-8) per bacterium per generation. Nitrate reductase and nitrite reductase appeared to be induced sequentially in strain 2184-D by the addition of nitrate. The formation of both of these enzymes was repressed by oxygen so that cells grown aerobically with nitrate possessed a low basal level of nitrate reducatase and exhibited no denitrification. The rate of synthesis of nitrate reductase increased quickly after addition of nitrate and removal of oxygen. It then declined to a lower steady-state level. Cells grown anaerobically with nitrate retained approximately 30 to 40% of the respiratory activity of aerobically grown cells. Aeration of anaerobically grown cells in the presence of amino acids increased the respiratory activity to normal aerobic levels. This aeration promoted rapid degradation of the existing nitrate reductase with or without the added amino acids.
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PMID:Influence of oxygen on development of nitrate respiration in Bacillus stearothermophilus. 578 97

The time course of appearance of respiratory nitrate reductase in Escherichia coli after induction by nitrate was analyzed under different conditions, and the inhibitory effects of oxygen, chloramphenicol, and rifampin were compared. Oxygen appeared to inhibit the synthesis of nitrate reductase at the level of transcription. In addition, the translation or some later steps of enzyme formation were blocked.
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PMID:Two sites of oxygen control in induced synthesis of respiratory nitrate reductase in Escherichia coli. 617 98


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