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 occurrence of the iron-reducing phenomenon among some common fungi was studied. Results indicated that (i) the reduction of ferric iron to the ferrous state by fungi seems to be restricted to nitrate reductase-inducible strains such as Actinomucor repens, Alternaria tenuis, Fusarium oxysporum, and F. solani and (ii) the amount of dissolved ferrous iron may be reduced progressively by increasing the amount of nitrate added to the medium. Compared with a complex medium (Sabouraud medium), less iron became reduced if NO(3) was the only nitrogen source (Czapek Dox medium). These data strongly support the view that ferric iron is acting as an hydrogen acceptor in respiration, competing with nitrate for electrons that are mediated by the enzyme nitrate reductase. The significance of this property from an ecological viewpoint is discussed.
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PMID:Enzymatic reduction of iron oxide by fungi. 1634 55

Nitric oxide (NO) and hydrogen peroxide (H(2)O(2)) are key signalling molecules produced in response to various stimuli and involved in a diverse range of plant signal transduction processes. Nitric oxide and H(2)O(2) have been identified as essential components of the complex signalling network inducing stomatal closure in response to the phytohormone abscisic acid (ABA). A close inter-relationship exists between ABA and the spatial and temporal production and action of both NO and H(2)O(2) in guard cells. This study shows that, in Arabidopsis thaliana guard cells, ABA-mediated NO generation is in fact dependent on ABA-induced H(2)O(2) production. Stomatal closure induced by H(2)O(2) is inhibited by the removal of NO with NO scavenger, and both ABA and H(2)O(2) stimulate guard cell NO synthesis. Conversely, NO-induced stomatal closure does not require H(2)O(2) synthesis nor does NO treatment induce H(2)O(2) production in guard cells. Tungstate inhibition of the NO-generating enzyme nitrate reductase (NR) attenuates NO production in response to nitrite in vitro and in response to H(2)O(2) and ABA in vivo. Genetic data demonstrate that NR is the major source of NO in guard cells in response to ABA-mediated H(2)O(2) synthesis. In the NR double mutant nia1, nia2 both ABA and H(2)O(2) fail to induce NO production or stomatal closure, but in the nitric oxide synthase deficient Atnos1 mutant, responses to H(2)O(2) are not impaired. Importantly, we show that in the NADPH oxidase deficient double mutant atrbohD/F, NO synthesis and stomatal closure to ABA are severely reduced, indicating that endogenous H(2)O(2) production induced by ABA is required for NO synthesis. In summary, our physiological and genetic data demonstrate a strong inter-relationship between ABA, endogenous H(2)O(2) and NO-induced stomatal closure.
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PMID:ABA-induced NO generation and stomatal closure in Arabidopsis are dependent on H2O2 synthesis. 1636 58

Plants have four nitric oxide synthase (NOS) enzymes. NOS1 appears mitochondrial, and inducible nitric oxide synthase (iNOS) chloroplastic. Distinct peroxisomal and apoplastic NOS enzymes are predicted. Nitrite-dependent NO synthesis is catalyzed by cytoplasmic nitrate reductase or a root plasma membrane enzyme, or occurs nonenzymatically. Nitric oxide undergoes both catalyzed and uncatalyzed oxidation. However, there is no evidence of reaction with superoxide, and S-nitrosylation reactions are unlikely except during hypoxia. The only proven direct targets of NO in plants are metalloenzymes and one metal complex. Nitric oxide inhibits apoplastic catalases/ascorbate peroxidases in some species but may stimulate these enzymes in others. Plants also have the NO response pathway involving cGMP, cADPR, and release of calcium from internal stores. Other known targets include chloroplast and mitochondrial electron transport. Nitric oxide suppresses Fenton chemistry by interacting with ferryl ion, preventing generation of hydroxyl radicals. Functions of NO in plant development, response to biotic and abiotic stressors, iron homeostasis, and regulation of respiration and photosynthesis may all be ascribed to interaction with one of these targets. Nitric oxide function in drought/abscisic acid (ABA)-induction of stomatal closure requires nitrate reductase and NOS1. Nitric oxide synthasel likely functions to produce sufficient NO to inhibit photosynthetic electron transport, allowing nitrite accumulation. Nitric oxide is produced during the hypersensitive response outside cells undergoing programmed cell death immediately prior to loss of plasma membrane integrity. A plasma membrane lipid-derived signal likely activates apoplastic NOS. Nitric oxide diffuses within the apoplast and signals neighboring cells via hydrogen peroxide (H2O2)-dependent induction of salicylic acid biosynthesis. Response to wounding appears to involve the same NOS and direct targets.
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PMID:Nitric oxide signaling in plants. 1649 76

This work is concerned with the metabolism of Caldithrix abyssi-an anaerobic, moderately thermophilic bacterium isolated from deep-sea hydrothermal vents of the Mid-Atlantic Ridge and representing a new, deeply deviated branch within the domain Bacteria. Cells of C. abyssi grown on acetate and nitrate, which was reduced to ammonium, possessed nitrate reductase activity and contained cytochromes of the b and c types. Utilization of acetate occurred as a result of the operation of the TCA and glyoxylate cycles. During growth of C. abyssi on yeast extract, fermentation with the formation of acetate, propionate, hydrogen, and CO2 occurred. In extracts of cells grown on yeast extract, acetate was produced from pyruvate with the involvement of the following enzymes: pyruvate:ferredoxin oxidoreductase (2.6 micromol/(min mg protein)), phosphate acetyltransferase (0.46 micromol/(min mg protein)), and acetate kinase (0.3 micromol/(min mg protein)). The activity of fumarate reductase (0.14 micromol/(min mg protein)), malate dehydrogenase (0.17 micromol/(min mg protein)), and fumarate hydratase (1.2 micromol/(min mg protein)), as well as the presence of cytochrome b, points to the formation of propionate via the methyl-malonyl-CoA pathway. The activity of antioxidant enzymes (catalase and superoxide dismutase) was detected. Thus, enzymatic mechanisms have been elucidated that allow C. abyssi to switch from fermentation to anaerobic respiration and to exist in the gradient of redox conditions characteristic of deep-sea hydrothermal vents.
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PMID:[Investigation of the catabolism of acetate and peptides in the new anaerobic thermophilic bacterium Caldithrix abyssi]. 1675 61

In cyanobacterial membranes photosynthetic light reaction and respiration are intertwined. It was shown that the single hydrogenase of Synechocystis sp. PCC 6803 is connected to the light reaction. We conducted measurements of hydrogenase activity, fermentative hydrogen evolution and photohydrogen production of deletion mutants of respiratory electron transport complexes. All single, double and triple mutants of the three terminal respiratory oxidases and the ndhB-mutant without a functional complex I were studied. After activating the hydrogenase by applying anaerobic conditions in the dark hydrogen production was measured at the onset of light. Under these conditions respiratory capacity and amount of photohydrogen produced were found to be inversely correlated. Especially the absence of the quinol oxidase induced an increased hydrogenase activity and an increased production of hydrogen in the light compared to wild type cells. Our results support that the hydrogenase as well as the quinol oxidase function as electron valves under low oxygen concentrations. When the activities of photosystem II and I (PSII and PSI) are not in equilibrium or in case that the light reaction is working at a higher pace than the dark reaction, the hydrogenase is necessary to prevent an acceptor side limitation of PSI, and the quinol oxidase to prevent an overreduction of the plastoquinone pool (acceptor side of PSII). Besides oxygen, nitrate assimilation was found to be an important electron sink. Inhibition of nitrate reductase resulted in an increased fermentative hydrogen production as well as higher amounts of photohydrogen.
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PMID:Inhibition of respiration and nitrate assimilation enhances photohydrogen evolution under low oxygen concentrations in Synechocystis sp. PCC 6803. 1727 45

Rapid-equilibrium rate equations for enzyme-catalyzed reactions are especially useful when the mechanism involves a number of pKs, but they are also useful when some reactants have stoichiometric numbers greater than one or hydrogen ions are produced or consumed in the rate-determining step. The pH dependencies of limiting velocities, Michaelis constants, and reaction velocities for the forward reaction are discussed for two examples of reductase reactions of the type mR + O -> products, where R is the reductant and O is the oxidant. For the nitrate reductase reaction (EC 1.9.6.1), m = 2 and two hydrogen ions are consumed. For the nitrite-ferredoxin reductase reaction (EC 1.7.7.1), m = 6 and eight hydrogen ions are consumed. The expressions for the limiting velocities, Michaelis constants, and rate equations for the forward reaction are derived for two ordered mechanisms and the random mechanism. Three Mathematica programs are used to make plots of kinetic parameters as functions of pH and three-dimensional plots of rapid-equilibrium velocities as functions of [O] and [R] for arbitrary sets of input parameters.
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PMID:Three mechanisms and rapid-equilibrium rate equations for a type of reductase reaction. 1792 31

Vascular tissue was recently shown to be capable of producing nitric oxide (NO), but the production sites and sources were not precisely determined. Here, NO synthesis was analysed in the phloem of Vicia faba in response to stress- and pathogen defence-related compounds. The chemical stimuli were added to shallow paradermal cortical cuts in the main veins of leaves attached to intact plants. NO production in the bare-lying phloem area was visualized by real-time confocal laser scanning microscopy using the NO-specific fluorochrome 4,5-diaminofluorescein diacetate (DAF-2 DA). Abundant NO generation in companion cells was induced by 500 microm salicylic acid (SA) and 10 microm hydrogen peroxide (H(2)O(2)), but the fungal elicitor chitooctaose was much less effective. Phloem NO production was found to be dependent on Ca(2+) and mitochondrial electron transport and pharmacological approaches found evidence for activity of a plant NO synthase but not a nitrate reductase. DAF fluorescence increased most strongly in companion cells and was occasionally observed in phloem parenchyma cells. Significantly, accumulation of NO in sieve elements could be demonstrated. These findings suggest that the phloem perceives and produces stress-related signals and that one mechanism of distal signalling involves the production and transport of NO in the phloem.
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PMID:Nitric oxide generation in Vicia faba phloem cells reveals them to be sensitive detectors as well as possible systemic transducers of stress signals. 1831 39

Nitric oxide (NO) is a bioactive molecule involved in many biological events, and has been reported as pro-oxidant as well as anti-oxidant in plants. In the present study, the sources of NO production under water stress, the role of NO in water stress-induced hydrogen peroxide (H2O2) accumulation and subcellular activities of anti-oxidant enzymes in leaves of maize (Zea mays L.) plants were investigated. Water stress induced defense increases in the generation of NO in maize mesphyll cells and the activity of nitric oxide synthase (NOS) in the cytosolic and microsomal fractions of maize leaves. Water stress-induced defense increases in the production of NO were blocked by pretreatments with inhibitors of NOS and nitrate reductase (NR), suggesting that NO is produced from NOS and NR in leaves of maize plants exposed to water stress. Water stress also induced increases in the activities of the chloroplastic and cytosolic anti-oxidant enzymes superoxide dismutase (SOD), ascorbate peroxidase (APX), and glutathione reductase (GR), and the increases in the activities of anti-oxidant enzymes were reduced by pretreatments with inhibitors of NOS and NR. Exogenous NO increases the activities of water stress-induced subcellular anti-oxidant enzymes, which decreases accumulation of H2O2. Our results suggest that NOS and NR are involved in water stress-induced NO production and NOS is the major source of NO. The potential ability of NO to scavenge H2O2 is, at least in part, due to the induction of a subcellular anti-oxidant defense.
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PMID:Nitric oxide reduces hydrogen peroxide accumulation involved in water stress-induced subcellular anti-oxidant defense in maize plants. 1871 46

Exclusion of combined nitrogen (NaNO3) from the growth medium caused certain changes in metabolic processes leading to cessation in growth of the non-heterocystous, non nitrogen-fixing marine cyanobacterium Oscillatoria willei BDU 130511. But antioxidative enzymes, namely superoxide dismutase and peroxidase, helped the organism to survive the nitrogen stress. Prominent effects observed during nitrogen starvation/limitation were: (i) reduction of major and accessory photosynthetic pigments, (ii) impairment of photosynthesis due to loss of one major Rubisco isoenzyme, (iii) reduced synthesis of lipids and fatty acids, (iv) modifications of protein synthesis leading to the repression of three polypeptides and synthesis of two new polypeptides, (v) enhanced glutamine synthetase and reduced nitrate reductase activities, (vi) enhanced production of hydrogen peroxide and (vii) induced appearance of four new peroxidase isoenzymes. The observed metabolic changes were reversible, and the arrested growth under prolonged nitrogen deficiency could be fully restored upon subculturing in freshly prepared ASN III medium containing nitrogen (NaNO3). The present study demonstrates the capability of a non-nitrogen-fixer to withstand nitrogen stress making it an ecologically successful organism in the marine environment. The above pleiotropic effects of nitrogen deficiency also demonstrate that nitrogen plays a crucial role in growth and metabolism of marine cyanobacteria.
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PMID:Nitrogen stress induced changes in the marine cyanobacterium Oscillatoria willei BDU 130511. 1971 95

At least theoretically, plants may synthesize nitric oxide (NO) either by reduction of N in higher oxidations states, or by oxidation of more reduced N-compounds. The well established reductive pathway uses nitrite as a substrate, produced by cytosolic nitrate reductase. The only oxidative pathway described so far comprises nitric oxide synthase (NOS)-like activity, where guanidino-N from L-arginine is oxidized to NO. In our previous paper we have demonstrated yet another form of oxidative NO formation, whereby hydroxylamine (HA), but also the AOX-inhibitor salicylhydroxamate (SHAM) is oxidized to NO by tobacco suspension cells. Oxidation of HA to NO was also demonstrated in vitro by using ROS producing enzymes. Apparently superoxide radicals and/or hydrogen peroxide served as oxidants. Another unexpected observation pointed to a special role for superoxide dismutase in oxidative NO formation.
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PMID:Oxidation of hydroxylamines to NO by plant cells. 1935 30


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