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)

Under anaerobic circumstances in the presence of nitrate Paracoccus denitrificans is able to denitrify. The properties of the reductases involved in nitrate reductase, nitrite reductase, nitric oxide reductase, and nitrous oxide reductase are described. For that purpose not only the properties of the enzymes of P. denitrificans are considered but also those from Escherichia coli, Pseudomonas aeruginosa, and Pseudomonas stutzeri. Nitrate reductase consists of three subunits: the alpha subunit contains the molybdenum cofactor, the beta subunit contains the iron sulfur clusters, and the gamma subunit is a special cytochrome b. Nitrate is reduced at the cytoplasmic side of the membrane and evidence for the presence of a nitrate-nitrite antiporter is presented. Electron flow is from ubiquinol via the specific cytochrome b to the nitrate reductase. Nitrite reductase (which is identical to cytochrome cd1) and nitrous oxide reductase are periplasmic proteins. Nitric oxide reductase is a membrane-bound enzyme. The bc1 complex is involved in electron flow to these reductases and the whole reaction takes place at the periplasmic side of the membrane. It is now firmly established that NO is an obligatory intermediate between nitrite and nitrous oxide. Nitrous oxide reductase is a multi-copper protein. A large number of genes is involved in the acquisition of molybdenum and copper, the formation of the molybdenum cofactor, and the insertion of the metals. It is estimated that at least 40 genes are involved in the process of denitrification. The control of the expression of these genes in P. denitrificans is totally unknown. As an example of such complex regulatory systems the function of the fnr, narX, and narL gene products in the expression of nitrate reductase in E. coli is described. The control of the effects of oxygen on the reduction of nitrate, nitrite, and nitrous oxide are discussed. Oxygen inhibits reduction of nitrate by prevention of nitrate uptake in the cell. In the case of nitrite and nitrous oxide a competition between reductases and oxidases for a limited supply of electrons from primary dehydrogenases seems to play an important role. Under some circumstances NO formed from nitrite may inhibit oxidases, resulting in a redistribution of electron flow from oxygen to nitrite. P. denitrificans contains three main oxidases: cytochrome aa3, cytochrome o, and cytochrome co. Cytochrome o is proton translocating and receives its electrons from ubiquinol. Some properties of cytochrome co, which receives its electrons from cytochrome c, are reported.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Metabolic regulation including anaerobic metabolism in Paracoccus denitrificans. 205 Jun 53

1. Nitrite and nitrate levels were measured in samples from ileostomy bags or stomal samples of thirty-one ileostomists (twenty-two ulcerative colitis, nine Crohn's disease), 14-16 h after ingestion of a conventional meal or a meal containing a high content of nitrite and nitrate. 2. Ileostomy samples were decolourized with barium chloride, sodium sulphate and charcoal. Nitrite was determined spectrophotometrically by the Griess reaction and nitrate determined as nitrite after reduction with nitrate reductase (EC 1.7.99.4) in the presence of sodium formate. The mean percentage recovery from twenty-six spiked samples was 101.9 (SE 3.5)% for nitrite and 82.9 (SE 3.3)% for nitrate. 3. Ileostomy bag samples were obtained in twenty-nine cases of which ten had measurable nitrite (median 0, range 0-20.7 nmol/g) on a conventional meal compared with twenty-three cases (median 7.2, range 0-31.1 nmol/g) on the test meal (P less than 0.01). Nitrate levels were measurable in sixteen (median 6.7, range 0-48.2 nmol/g) after a conventional meal compared with twenty-one (median 20.5, range 0-53.2 nmol/g) after the test meal (P less than 0.01). 4. Stomal fresh-catch samples were obtained in twenty-four cases: combined nitrate and nitrite was higher in eighteen, lower in four and unchanged in two subjects after the test meal (P less than 0.05). 5. The type of foodstuff ingested can significantly alter measurable levels of nitrite-nitrate in the distal ileum and is one factor determining nitrite-nitrate input into the proximal colon.
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PMID:Nitrite and nitrate levels in ileostomy effluent: effect of dietary change. 270 31

Nitrite production by nodules and roots of pea plants (Pisum sativum L., cultivar Alaska) inoculated with Rhizobium leguminosarum strain 3855 has been studied. Nitrate reductase (NR) activity and nitrite reductase (NiR) activity of the bacteroidal and cytosolic fractions of the nodules were also determined, as well as the nitrite content of the nodules cytosol. Nitrite production by nodules and roots from plants treated with 5 mM KNO3 was higher than that of nodules and roots from plants not treated with nitrate, and regardless of the nitrate treatment, nitrite production increased with the incubation period. The presence of nitrate, propanol or both compounds in the incubation mixtures significantly increased the nitrite production by nodules and roots. Nitrite reductase activity was detected in fresh by isolated bacteroids of R. leguminosarum strain 3855, although the presence of nitrate reductase activity could not be detected both in bacteroids of nodules isolated from plants treated or not with 5 mM KNO3. After isolation, when bacteroids were incubated in a mixture with nitrate, nitrate reductase activity developed after incubation for 12 h. Consequently, there was an increase in nitrite reductase activity, which resulted in the disappearance of the nitrite previously accumulated in the incubation medium. Nitrate utilization by bacteroids was not detected until 5 h from the beginning of the incubation period. Since the presence of chloramphenicol or rifampicin in the incubation medium prevented the development of the nitrate reductase activity, such activity was induced in bacteroids. Nitrite content and nitrate reductase and nitrite reductase activities of the cytosol from nodules of pea plants treated or not with 5 mM KNO3 varied with the buffer used for nodules homogenization. However, no nitrite was found when nodules were homogenized with ethanol, what indicates that nitrite accumulation in the cytosol occurs during the homogenization process of the nodules.
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PMID:[Utilization of nitrate by bacteroids and cytosol of nodules formed by Rhizobium leguminosarum]. 280 36

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

1. The assimilatory nitrite reductase of the N(2)-fixing bacterium Azotobacter chroococcum was prepared in a soluble form from cells grown aerobically with nitrate as the nitrogen source, and some of its properties have been studied. 2. The enzyme is a FAD-dependent metalloprotein (mol.wt. about 67000), which stoicheiometrically catalyses the direct reduction of nitrite to NH(3) with NADH as the electron donor. 3. NADH-nitrite reductase can exist in two either active or inactive interconvertible forms. Inactivation in vitro can be achieved by preincubation with NADH. Nitrite can specifically protect the enzyme against this inactivation and reverse the process once it has occurred. 4. A. chroococcum nitrite reductase is an adaptive enzyme whose formation depends on the presence of either nitrate or nitrite in the nutrient solution. 5. Tungstate inhibits growth of the microorganism very efficiently, by competition with molybdate, when nitrate is the nitrogen source, but does not interfere when nitrite or NH(3) is substituted for nitrate. The addition of tungstate to the culture media results in the loss of nitrate reductase activity but does not affect nitrite reductase.
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PMID:Reduced nicotinamide-adenine dinucleotide-nitrite reductase from Azotobacter chroococcum. 414 87

1. Nitrate induces the development of NADH-nitrate reductase (EC 1.6.6.1), FMNH(2)-nitrate reductase and NADH-cytochrome c reductase activities in barley shoots. 2. Sucrose-density-gradient analysis shows one band of NADH-nitrate reductase (8S), one band of FMNH(2)-nitrate reductase activity (8S) and three bands of NADH-cytochrome c reductase activity (bottom layer, 8S and 3.7S). Both 8S and 3.7S NADH-cytochrome c reductase activities are inducible by nitrate, but the induction of the 8S band is much more marked. 3. The 8S NADH-cytochrome c reductase band co-sediments with both NADH-nitrate reductase activity and FMNH(2)-nitrate reductase activity. Nitrite reductase activity (4.6S) did not coincide with the activity of either the 8S or the 3.7S NADH-cytochrome c reductase. 4. FMNH(2)-nitrate reductase activity is more stable (t((1/2)) 12.5min) than either NADH-nitrate reductase activity (t((1/2)) 0.5min) or total NADH-cytochrome c reductase activity (t((1/2)) 1.5min) at 45 degrees C. 5. NADH-cytochrome c reductase and NADH-nitrate reductase activities are more sensitive to p-chloromercuribenzoate than is FMNH(2)-nitrate reductase activity. 6. Tungstate prevents the formation of NADH-nitrate reductase and FMNH(2)-nitrate reductase activities, but it causes superinduction of NADH-cytochrome c reductase activity. Molybdate overcomes the effects of tungstate. 7. The same three bands (bottom layer, 8S and 3.7S) of NADH-cytochrome c reductase activity are observed irrespective of whether induction is carried out in the presence or absence of tungstate, but only the activities in the 8S and 3.7S bands are increased. 8. The results support the idea that NADH-nitrate reductase, FMNH(2)-nitrate reductase and NADH-cytochrome c reductase are activities of the same enzyme complex, and that in the presence of tungstate the 8S enzyme complex is formed but is functional only with respect to NADH-cytochrome c reductase activity.
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PMID:Structural and functional relationships of enzyme activities induced by nitrate in barley. 432 54

The reductase enzymes in Nitrosomonas and Nitrobacter were studied under anaerobic conditions when the oxidase enzymes were inactive. The most effective electron-donor systems for nitrate reductase in Nitrobacter were reduced benzyl viologen alone, phenazine methosulphate with either NADH or NADPH, and FMN or FAD with NADH. Nitrite and hydroxylamine reductases were found in both nitrifying bacteria, and optimum activity for each enzyme was obtained with NADH or NADPH with either FMN or FAD. The product of both these enzymes was identified as ammonia. In extracts of Nitrosomonas the ammonia was further utilized by an NADPH-specific glutamate dehydrogenase. (15)N-labelled nitrite, hydroxylamine and ammonia were rapidly incorporated into cell protein by Nitrosomonas, and Nitrobacter in addition incorporated [(15)N]nitrate. Relatively gentle methods of cell disruption were compared with ultrasonic treatment, to enable a more exact study to be undertaken of the intracellular distribution of the oxidase and reductase enzymes. The functional relationship of these opposing enzyme systems in the nitrifying bacteria is considered.
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PMID:Properties of some reductase enzymes in the nitrifying bacteria and their relationship to the oxidase systems. 438 32

Nitrite oxidase and nitrate reductase in Nitrobacter agilis were shown to be separate enzymes. The best separation of the two systems was achieved by ammonium sulphate fractionation. The effects of various compounds, including antimycin A, 2-n-heptyl-4-hydroxyquinoline N-oxide and chlorate, also clearly distinguish between the two enzyme reactions. The relationship between the two opposing reactions in Nitrobacter is discussed.
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PMID:Nitrite oxidase and nitrate reductase in Nitrobacter agilis. 580 6

Low concentrations (1-50mum) of ubiquinol(1) were rapidly oxidized by spheroplasts of Escherichia coli derepressed for synthesis of nitrate reductase using either nitrate or oxygen as electron acceptor. Oxidation of ubiquinol(1) drove an outward translocation of protons with a corrected -->H(+)/2e(-) stoichiometry [Scholes & Mitchell (1970) J. Bioenerg.1, 309-323] of 1.49 when nitrate was the acceptor and 2.28 when oxygen was the acceptor. Proton translocation driven by the oxidation of added ubiquinol(1) was also observed in spheroplasts from a double quinone-deficient mutant strain AN384 (ubiA(-)menA(-)), whereas a haem-deficient mutant, strain A1004a, did not oxidize ubiquinol(1). Proton translocation was not observed if either the protonophore carbonyl cyanide m-chlorophenylhydrazone or the respiratory inhibitor 2-n-heptyl-4-hydroxyquinoline N-oxide was present. When spheroplasts oxidized Diquat radical (DQ(+)) to the oxidized species (DQ(++)) with nitrate as acceptor, nitrate was reduced to nitrite according to the reaction: [Formula: see text] and nitrite was further reduced in the reaction: [Formula: see text] Nitrite reductase activity (2) was inhibited by CO, leaving nitrate reductase activity (1) unaffected. Benzyl Viologen radical (BV(+)) is able to cross the cytoplasmic membrane and is oxidized directly by nitrate reductase to the divalent cation, BV(++). In the presence of CO, this reaction consumes two protons: [Formula: see text] The consumption of these protons could not be detected by a pH electrode in the extra-cellular bulk phase of a suspension of spheroplasts unless the cytoplasmic membrane was made permeable to protons by the addition of nigericin or tetrachlorosalicylanilide. It is concluded that the protons of eqn. (3) are consumed at the cytoplasmic aspect of the cytoplasmic membrane. Diquat radical, reduced N-methylphenazonium methosulphate and its sulphonated analogue N-methylphenazonium-3-sulphonate (PMSH) and ubiquinol(1) are all oxidized by nitrate reductase via a haem-dependent, endogenous quinone-independent, 2-n-heptyl-4-hydroxyquinoline N-oxide-sensitive pathway. Approximate-->H(+)/2e(-) stoichiometries were zero with Diquat radical, an electron donor, 1.0 with reduced N-methylphenazonium methosulphate or its sulphonated analogue, both hydride donors, and 2.0 with ubiquinol(1) (QH(2)), a hydrogen donor. It is concluded that the protons appearing in the medium are derived from the reductant and the observed-->H(+)/2e(-) stoichiometries are accounted for by the following reactions occurring at the periplasmic aspect of the cytoplasmic membrane.: [Formula: see text]
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PMID:The mechanism of proton translocation driven by the respiratory nitrate reductase complex of Escherichia coli. 625 43

Nitrate reductase (NADPH:nitrate oxidoreductase; EC 1.6.6.1-3) was purified to apparent homogeneity from mycelium of Penicillium chrysogenum. The final preparation catalyzed the NADPH-dependent, FAD-mediated reduction of nitrate with a specific activity of 170-225 units X mg of protein-1. Gel filtration and glycerol density centrifugation yielded, respectively, a Stokes radius of 6.3 nm and an s20,w of 7.4. The molecular weight was calculated to be 199,000. On sodium dodecyl sulfate gels, the enzyme displayed two almost contiguous dye-staining bands corresponding to molecular weights of about 97,000 and 98,000. The enzyme prefers NADPH to NADH (kspec ratio = 2813), FAD to FMN (kspec ratio = 141), FAD (+ NADPH) to FADH2 (kspec ratio = 12,000), and nitrate to chlorate (kspec ratio = 4.33), where the kspec (the specificity constant for a given substrate) represents Vmax/Km. The Penicillium enzyme will also catalyze te NADPH-dependent, FAD-mediated reduction of cytochrome c with a specific activity of 647 units X mg of protein-1 (Kmcyt = 1.25 X 10(-5) M), and the reduced methyl viologen (MVH2, i.e. methyl viologen + dithionite)-dependent, NADPH and FAD-independent reduction of nitrate with a specific activity of 250 units X mg of protein-1 kmMVH2 = 3.5 X 10(-6) M). Initial velocity studies showed intersecting NADPH-FAD and nitrate-FAD reciprocal plot patterns. The NADPH-nitrate pattern was a series of parallel lines at saturating and unsaturating FAD levels. NADP+ was competitive with NADPH, uncompetitive with nitrate (at saturating and unsaturating FAD levels), and a mixed-type inhibitor with respect to FAD. Nitrite was competitive with nitrate, uncompetitive with NADPH (at saturating and unsaturating FAD levels), and a mixed-type inhibitor with respect to FAD. At unsaturating nitrate and FAD, NADPH exhibited substrate inhibition, perhaps as a result of binding to the FAD site(s). At very low FAD concentrations, low concentrations of NADP+ activated the reaction slightly. The initial velocity and product inhibition patterns are consistent with either of the two kinetic mechanisms. One (rather unlikely) mechanism involves the rapid equilibrium random binding of all ligands with (a) NADP+ and NADPH mutually exclusive, (b) nitrate and nitrite mutually exclusive, (c) the binding of NADPH strongly inhibiting the binding of nitrate and vice versa, (d) the binding of NADPH strongly promoting the binding of nitrite and vice versa, and (e) the binding of nitrate strongly promoting the binding of NADP+ and vice versa...
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PMID:Nitrate reductase from Penicillium chrysogenum. Purification and kinetic mechanism. 679 May 45


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