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

---

Query: EC:1.7.1.2 (nitrate reductase)
3,861 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

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.
...
PMID:Temporary low oxygen conditions for the formation of nitrate reductase and nitrous oxide reductase by denitrifying Pseudomonas sp. G59. 374 33

Male Sprague-Dawley rats were fed a purified fibre-free diet containing 5% (w/w) sodium saccharin for 4 weeks or 20 weeks and changes in caecal bacterial numbers and enzyme activities (endogenous ammonia production, beta-glucosidase, beta-glucuronidase, nitrate reductase, nitroreductase, aryl sulphatase) determined in vitro. Saccharin treatment gave marked caecal enlargement but had no effect on bacterial concentration at either treatment period, and significantly decreased beta-glucuronidase, nitrate reductase and sulphatase activities/g caecal contents. The incubation of a suspension of caecal contents from control rats with saccharin (75 mM) in vitro inhibited beta-glucuronidase and nitrate reductase activities, and ammonia production from endogenous substrates. Such changes may decrease the rate of formation of toxic bacterial products in the hindgut.
...
PMID:Modification of rat caecal microbial biotransformation activities by dietary saccharin. 384 Feb 94

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.
...
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

NADH:nitrate reductase (EC 1.6.6.1) was isolated from squash cotyledons (Cucurbita maxima L.) by a combination of Blue Sepharose and zinc-chelate affinity chromatographies followed by gel filtration on Bio-Gel A-1.5m. These preparations gave a single protein staining band (Mr = 115,000) on sodium dodecyl sulfate gel electrophoresis, indicating that the enzyme is homogeneous. The native Mr of nitrate reductase was found to be 230,000, with a minor form of Mr = 420,000 also occurring. These results indicate that the native nitrate reductase is a homodimer of Mr = 115,000 subunits. Acidic amino acids predominate over basic amino acids, as shown both by the amino acid composition of the enzyme and an isoelectric point for nitrate reductase of 5.7. The homogeneous nitrate reductase had a UV/visible spectrum typical of a b-type cytochrome. The enzyme was found to contain one each of flavin (as FAD), heme iron, molybdenum, and Mo-pterin/Mr = 115,000 subunit. A model is proposed for squash nitrate reductase in which two Mr = 115,000 subunits are joined to made the native enzyme. Each subunit contains 1 eq of FAD, cytochrome b, and molybdenum/Mo-pterin.
...
PMID:Quaternary structure and composition of squash NADH:nitrate reductase. 403 8

Membranes were isolated from Bacillus stearothermophilus 2184D by lysozyme digestion of the cell wall and subsequent differential centrifugation. Observations with the electron microscope indicate that such membranes are relatively intact and have a typical membrane appearance. Nitrate will preferentially oxidize the cytochrome b of such membranes. Approximately 80% of the total respiratory nitrate reductase activity of whole cells can be localized in the washed membrane fraction and the process of membrane isolation results in a sixfold purification of this enzyme. Of several detergents tested, sodium dodecyl sulfate, Triton 114, and Triton X-100 are most effective in converting reduced methyl viologen-nitrate reductase to a form which will not pellet at 130,000 x g. Density gradient analysis reveals that such detergent-mediated solubilization converts virtually all membrane protein to a form of lighter density.
...
PMID:Localization and solubilization of the respiratory nitrate reductase of Bacillus stearothermophilus. 433 9

Isolated membranes of Bacillus stearothermophilus 2184D can be disrupted by treatment with sodium dodecyl sulfate (SDS). This disruption is attended by a decreased turbidity of membrane suspensions and a differential loss of activities of the electron transport system. Reduced methyl viologen (MVH)-nitrate reductase activity is insensitive to SDS treatment, whereas reduced nicotinamide adenine dinucleotide (NADH)-nitrate reductase and cyanide-sensitive NADH oxidase activities are decreased by 80% at an SDS concentration of 0.5 mg/mg of membrane protein. NADH-menadione reductase activity is unaffected at this SDS concentration, but at higher detergent levels it also decreases in activity. The abilities of NADH to reduce and nitrate to oxidize the cytochrome components of the membrane were also decreased after SDS treatment. Dilution of solubilized membrane in buffer containing divalent cation results in formation of an aggregate with an increased turbidity and reconstituted NADH-nitrate reductase and cyanide-sensitive NADH oxidase activities. Of several cations tested, magnesium was the most effective, and the reconstitution process was pH-dependent with an optimum at pH 7.4. Intact and aggregated membranes had similar densities and cytochrome contents, and the sensitivity of NADH-nitrate reductase to several inhibitors was similar in intact and reconstituted membranes.
...
PMID:Physical aggregation and functional reconstitution of solubilized membranes of Bacillus stearothermophilus. 433 10

White bands resulting from precipitation of dodecan-1-ol liberated by hydrolysis of sodium dodecyl sulfate and decan-5-ol released by hydrolysis of decan-5-yl sulfate produced zymograms of the primary and secondary alkylsulfatases from Pseudomonas C(12)B. Gas-liquid chromatographic analyses of ether extracts of the precipitate-containing segments of the zymograms confirmed the identity of the alcohols which were not discerned in extracts of segments of the gels other than those containing precipitates. beta-Galactosidase from Escherichia coli was marked on zymograms by the liberation of o-nitrophenol from o-nitrophenyl-beta-D-galactoside, and arylsulfatase from Pseudomonas C(12)B was marked in gels by liberation of p-nitrophenol from p-nitrophenyl sulfate. Membrane-associated dissimilatory nitrate reductases from a nitrate respirer (Enterobacter aerogenes) and a denitrifier (Pseudomonas perfectomarinus) did not penetrate either 6.8 or 3% polyacrylamide gel but were demonstrable at the top of the gels. In the membrane-bound state, formate served as electron donor for nitrate reductase from E. aerogenes, and reduced nicotinamide adenine dinucleotide (NADH) served as donor for nitrate reductase from P. perfectomarinus. Both enzymes reduced nitrate at the expense of reduced benzyl viologen as well. Assimilatory nitrate reductase from E. aerogenes moved easily into the 6.8% gels (R(f) = 0.43 under the conditions of these experiments). The reduced dye served as electron donor for the assimilatory reductase, but formate and NADH did not. Incubation of the membrane-associated nitrate reductases with 2% Triton X-100 solubilized the enzymes and removed the capacity of formate and NADH to serve as electron donors. Both retained the ability to reduce nitrate at the expense of reduced benzyl viologen. The solubilized dissimilatory reductase from E. aerogenes moved further in the gels (R(f) = 0.49) than the soluble assimilatory reductase; the solubilized dissimilatory reductase from the denitrifier, P. perfectomarinus, moved further in the gels (R(f) = 0.64) than either of the enzymes from E. aerogenes.
...
PMID:Methods for visualization of enzymes in polyacrylamide gels. 435 59

An investigation has been made to determine the effectiveness of univalent cations as cofactors for the inductive synthesis of nitrate reductase. In these experiments K(+) functions more effectively as the univalent cation activator than other univalent cations. Substitution of Rb(+) for K(+) resulted in enzyme formation at a rate of about one-half of that obtained with K(+). Sodium, Li(+), or NH(4) (+) either failed to stimulate or completely inhibited the inductive formation of the enzyme. When no univalent cations were present in the induction medium, enzyme formation was delayed for an initial 3-hour period in contrast to the normal one-hour delay in enzyme formation where adequate K(+) was present in the induction medium. During the period of inductive formation of nitrate reductase the activity of pyruvic kinase, a constitutive enzyme, was assayed under conditions where adequate K(+) was present. Results indicate that the presence of the different univalent cations in the induction medium had no striking effect on the activity of this enzyme during the induction period.
...
PMID:Effects of univalent cations on the inductive formation of nitrate reductase. 595 44

An assay method is described for measurement of absolute concentrations of the molybdenum cofactor, based on complementation of the defective nitrate reductase ('apo nitrate reductase') in extracts of the nit-1 mutant of Neurospora crassa. A number of alternative methods are described for preparing, anaerobically, molybdenum-cofactor-containing solutions from sulphite oxidase, xanthine oxidase and desulpho xanthine oxidase. For assay, these were mixed with an excess of extract of the nit-1 mutant, incubated for 24 h at 3.5 degrees C then assayed for NADPH:nitrate reductase activity. In all cases, the specific activity of the molybdenum cofactor, expressed as mumol of NO2-formed/min per ng-atom of Mo added from the denatured molybdoenzyme , was 25 +/- 4, a value that agrees with the known catalytic activity of the nitrate reductase of wild-type Neurospora crassa. This indicates that, under our conditions, there was quantitative transfer of the molybdenum cofactor from denatured molybdoenzyme to yield fully active nitrate reductase. Comparable cofactor assay methods of previous workers, apparently indicating transfer efficiencies of at best a few per cent, have never excluded satisfactorily the possibility that cofactor activity arose, not from stoichiometric constituents of the molybdoenzymes , but from contaminants. The following factors were investigated separately in developing the assay:the efficiency of extraction of the cofactor from the original enzyme, the efficiency of the complementation reaction between cofactor and apo nitrate reductase, and the assay of the resultant nitrate reductase, which must be carried out under non-inhibitory conditions. Though the cofactor is unstable in air (t1/2 about 15 min at 3.5 degrees C), it is stable when kept anaerobic in the presence of sodium dithionite, in aqueous solution or in dimethyl sulphoxide (activity lost at the rate of about 3%/24 h at 20-25 degrees C). Studies of stabilities, and investigations of the effect of added molybdate on the assay, permit conclusions to be drawn about the ligation of molybdenum to the cofactor and about steps in incorporation of the cofactor into the apoenzyme. Though the development of nitrate reductase activity is slow at 3.5 degrees C (t1/2 1.5-3 h) the complementation reaction may be carried out in high yield, aerobically. This is ascribed to rapid formation of an air-stable but catalytically inactive complex of the cofactor, as a precursor of the active nitrate reductase.(ABSTRACT TRUNCATED AT 400 WORDS)
...
PMID:Quantitative transfer of the molybdenum cofactor from xanthine oxidase and from sulphite oxidase to the deficient enzyme of the nit-1 mutant of Neurospora crassa to yield active nitrate reductase. 623 82

Membrane-bound nitrate reductase purified from Escherichia coli was resolved into two separate forms. The majority of the enzyme complex had a subunit composition of 2A:2B:4C, exhibited cytochrome b spectra, and was found to be stable after purification. A second form of nitrate reductase activity was a modified complex with a subunit composition of 2A:2B and lacked cytochrome. The subunit B from this complex was altered in its mobility on sodium dodecyl sulfate-polyacrylamide gels. The cytochrome-containing enzyme had 28 +/- 2 atoms of iron and 1.35 atoms of molybdenum whereas iron and molybdenum in cytochromeless enzyme were 24 +/- 2 atoms and 1.18 atoms/molecule, respectively. Besides cytochrome-containing nitrate reductase, two other cytochrome b-containing fractions were also resolved. These were cytochrome b associated with formate dehydrogenase and a novel cytochrome b with reduced absorption maxima at 430, 529.5, and 560 nm. Nitrate reductase cytochrome b (subunit C) was isolated from subunits A and B as a partially denatured form and its renaturation was accomplished by dialyzing against hemin. The renatured cytochrome yielded absorption spectra similar to the holoenzyme. The pure cytochrome aggregated upon heating, even in the presence of sodium dodecyl sulfate. It had a high isoelectric point (pH greater than 9.5) and had 45% hydrophobic amino acids.
...
PMID:Cytochrome b from Escherichia coli nitrate reductase. Its properties and association with the enzyme complex. 634 95


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---