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)

The three enzymes of the arginine deiminase pathway in Pseudomonas aeruginosa strain PAO were induced strongly (50- to 100-fold) by a shift from aerobic growth conditions to very low oxygen tension. Arginine in the culture medium was not essential for induction, but increased the maximum enzyme levels twofold. The induction of the three enzymes arginine deiminase (EC 3.5.3.6), catabolic ornithine carbamoyltransferase (EC 2.1.3.3), and carbamate kinase (EC 2.7.2.3) appeared to be coordinate. Catabolic ornithine carbamoyltransferase was studied in most detail. Nitrate and nitrite, which can replace oxygen as terminal electron acceptors in P. aeruginosa, partially prevented enzyme induction by low oxygen tension in the wild-type strain, but not in nar (nitrate reductase-negative) mutants. Glucose was found to exert catabolite repression of the deiminase pathway. Generally, conditions of stress, such as depletion of the carbon and energy source or the phosphate source, resulted in induced synthesis of catabolic ornithine carbamoyltransferase. The induction of the deiminase pathway is thought to mobilize intra- and extracellular reserves of arginine, which is used as a source of adenosine 5'-triphosphate in the absence of respiration.
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PMID:Regulation of enzyme synthesis in the arginine deiminase pathway of Pseudomonas aeruginosa. 625 88

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

Sensory transduction in aerotaxis required electron transport, in contrast to chemotaxis, which is independent of electron transport. Assays for aerotaxis were developed by employing spatial and temporal oxygen gradients imposed independently of respiration. By varying the step increase in oxygen concentration in the temporal assay, the dose-response relationship was obtained for aerotaxis in Salmonella typhimurium. A half-maximal response at 0.4 microM oxygen and inhibition by 5 mM KCN suggested that the "receptor" for aerotaxis is cytochrome o. The response was independent of adenosine triphosphate formation via oxidative phosphorylation but did correlate with changes in membrane potential monitored with the fluorescent cyanine dye diS-C3-(5). Nitrate and fumarate, which are alternative electron acceptors for the respiratory chain in S. typhimurium, inhibited aerotaxis when nitrate reductase and fumarate reductase were induced. These results support the hypothesis that taxis to oxygen, nitrate, and fumarate is mediated by the electron transport system and by changes in the proton motive force. Aerotaxis was normal in Escherichia coli mutants that were defective in the tsr, tar, or trg genes; in S. typhimurium, oxygen did not stimulate methylation of the products of these genes. A cheC mutant which shows an inverse response to chemoattractants also gave an inverse response to oxygen. Therefore, aerotaxis is transduced by a distinct and unidentified signally protein but is focused into the common chemosensory pathway before the step involving the cheC product. When S. typhimurium became anaerobic, the decreased proton motive force from glycolysis supported slow swimming but not tumbling, indicating that a minimum proton motive force was required for tumbling. The bacteria rapidly adapted to the anaerobic condition and resumed tumbling after about 3 min. The adaptation period was much shorter when the bacteria had been previously grown anaerobically.
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PMID:Aerotaxis in Salmonella typhimurium: role of electron transport. 625 58

When strains and mutants of the strictly aerobic hydrogen-oxidizing bacterium Alcaligenes eutrophus are grown heterotrophically on gluconate or fructose and are subsequently exposed to anaerobic conditions in the presence of the organic substrates, molecular hydrogen is evolved. Hydrogen evolution started immediately after the suspension was flushed with nitrogen, reached maximum rates of 70 to 100 mumol of H2 per h per g of protein, and continued with slowly decreasing rates for at least 18 h. The addition of oxygen to an H2-evolving culture, as well as the addition of nitrate to cells (which had formed the dissimilatory nitrate reductase system during the preceding growth), caused immediate cessation of hydrogen evolution. Formate is not the source of H2 evolution. The rates of H2 evolution with formate as the substrate were lower than those with gluconate. The formate hydrogenlyase system was not detectable in intact cells or crude cell extracts. Rather the cytoplasmic, NAD-reducing hydrogenase is involved by catalyzing the release of excessive reducing equivalents under anaerobic conditions in the absence of suitable electron acceptors. This conclusion is based on the following experimental results. H2 is formed only by cells which had synthesized the hydrogenases during growth. Mutants lacking the membrane-bound hydrogenase were still able to evolve H2. Mutants lacking the NAD-reducing or both hydrogenases were unable to evolve H2.
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PMID:Hydrogen evolution by strictly aerobic hydrogen bacteria under anaerobic conditions. 637 84

Mud1 insertion mutants of Escherichia coli were obtained in which the lac structural genes were fused to the promoter of torA, a gene encoding the trimethylamine N-oxide (TMAO) reductase. Expression of the fusion is induced by TMAO and repressed by oxygen. However, in contrast to the nar operon which codes for the nitrate reductase structural genes, the tor::Mud1 fusion was found to be independent of the positive control exerted by the nirR gene product and not repressed by the molybdenum cofactor. The torA gene which is strongly linked to pyrF (28.3U) is different from any tor gene already described in E. coli or in Salmonella typhimurium.
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PMID:Regulation of the trimethylamine N-oxide (TMAO) reductase in Escherichia coli: analysis of tor::Mud1 operon fusion. 638 91

The protein composition of the cytoplasmic membranes of Escherichia coli, grown aerobically and anaerobically on a glucose minimal medium at pH 7.0, were analyzed by crossed immunoelectrophoresis. Qualitative differences are limited to only two proteins: nitrate reductase (E.C. 1.7.99.4) is absent under aerobic growth conditions, whereas an unidentified protein, with a molecular weight of 81,500 and located at the inner side of the cytoplasmic membrane, is synthesized only in the presence of oxygen. Quantitative differences are observed for many proteins: the ratio of the amount of a specific protein present in cells grown anaerobically and aerobically was, for four proteins, between 0.3 and 1; for 25 proteins, between 1 and 3; and for five proteins, larger than 5.
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PMID:The protein composition of the cytoplasmic membrane of aerobically and anaerobically grown Escherichia coli. 639 89

The in vivo stability of ferredoxin-nitrate reductase from the cyanobacterium Anacystis nidulans under conditions of inhibited protein synthesis has been studied in nitrate-grown cells. A light-promoted rapid decay in cellular nitrate reductase activity took place in the absence of any added nitrogen source, but not in the presence of nitrate, nitrite, or ammonium. The inactivation process seemed to proceed in two sequential steps. The first step required both light and oxygen, and was inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) or, to a lesser extent, by sulfhydryl-containing compounds. The resulting inactive form of nitrate reductase, apparently suffering from an oxidative modification, could be reactivated in vivo either by switching-off the light or by addition of inorganic nitrogenous compounds. Prolonged illumination of the cells in the absence of a nitrogen source led to further modification of the enzyme, which could not be reversed. Stability of the active enzyme appears to be a decisive factor contributing to the determination of the actual level of nitrate reductase in A. nidulans cells.
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PMID:Regulation of the nitrate reductase level in anacystis nidulans: activity decay under nitrogen stress. 643 30

The regulation of synthesis of the hydrogenase which is a component of the formate hydrogen-lyase complex was studied by means of a strain of Escherichia coli possessing a transcriptional fusion of the hydrogenase gene (hyd) with the lacZ gene (hyd::lac fusion). Formation of active hydrogenase in the wild strain requires the presence of nickel in the medium; transcription of the hyd gene, however, is independent from the presence of Ni2+. Ni2+ addition to Ni2+-prestarved cells did not lead to any activation of presumptive hydrogenase apoprotein. Regulatory mutants were isolated in which nitrate repression of hyd::lac expression was relieved. Two main classes of regulatory mutants were identified: (i) Mutants with a defect in nitrate reductase; (ii) mutants with a cis-dominant regulatory mutation closely linked to the hyd::lac fusion. In the presence of formate which acts as an inducer, the hyd::lac fusion was also expressed under aerobic conditions. The results infer that nitrate repression of transcription of the hydrogenase structural gene is not effected by nitrate itself but requires the function of the electron transport chain leading to nitrate and that mutations in the promoter/operator region of the hyd cistron may confer insensitivity to redox control both by oxygen and nitrate.
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PMID:Regulation of the synthesis of hydrogenase (formate hydrogen-lyase linked) of E. coli. 644 May 7

Strains carrying operon fusions between the promotor of the chl I gene and the lac structural genes were constructed. From these strains in which the expression of the lac genes is under the control of both nitrate and oxygen, spontaneous regulatory mutants were selected: (i) mutants which synthesize beta-galactosidase constitutively in anaerobiosis; (ii) mutants in which beta-galactosidase synthesis is no longer repressed by oxygen. Introduction of the nir R mutated allele into strains carrying these fusions resulted in the total loss of beta-galactosidase synthesis, confirming that nir R is a regulatory gene controlling the expression of the biosynthesis of the nitrate reductase.
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PMID:Operon fusions in the nitrate reductase operon and study of the control gene nir R in Escherichia coli. 645 62

In anaerobically grown Paracoccus denitrificans the dissimilatory nitrate reductase is linked to the respiratory chain at the level of cytochromes b. Electron transport to nitrite and nitrous oxide involves c-type cytochromes. During electron transport from NADH to nitrate one phosphorylation site is passed, whereas two sites are passed during electron transport from NADH to oxygen, nitrite and nitrous oxide. The presentation of a respiratory chain as a linear array of electron carriers gives a misleading picture of the efficiency of energy conservation since the location of the reductases is not taken into account. For the reduction of nitrite and nitrous oxide, protons are utilized from the periplasmic space, whereas for the reduction of oxygen and nitrate, protons are utilized from the cytoplasmic side of the inner membrane. Evidence for two transport systems for nitrate was obtained. One is driven by the proton motive force; this system is used to initiate nitrate reduction. The second system is a nitrate-nitrite antiport system. A scheme for proton translocation and electron transport to nitrate, nitrite, nitrous oxide and oxygen is presented. The number of charges translocated across the membrane during flow of two electrons from NADH is the same for all nitrogenous oxides and is 67-71% of that during electron transfer to oxygen via cytochrome o. These findings are in accordance with growth yield studies. YMAX electron values determined in chemostat cultures for growth with various substrates and hydrogen acceptors are proportional to the number of charges translocated to these hydrogen acceptors during electron transport.
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PMID:The bioenergetics of denitrification. 676 47


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