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)

In the present study nitrate uptake by maize (Zea mays L.) roots was investigated in the presence or absence of ferricyanide (hexacyanoferrate III) or dicumarol. Nitrate uptake caused an alkalization of the medium. Nitrate uptake of intact maize seedlings was inhibited by ferricyanide while the effect of dicumarol was not very pronounced. Nitrite was not detected in the incubation medium, neither with dicumarol-treated nor with control plants after application of 100 microM nitrate to the incubation solution. In a second set of experiments interactions between nitrate and ferricyanide were investigated in vivo and in vitro. Nitrate (1 or 3 mM) did neither influence ferricyanide reductase activity of intact maize roots nor NADH-ferricyanide oxidoreductase activity of isolated plasma membranes. Nitrate reductase activity of plasma-membrane-enriched fractions was slightly stimulated by 25 microM dicumarol but was not altered by 100 microM dicumarol, while NADH-ferricyanide oxidoreductase activity was inhibited in the presence of dicumarol. These data suggest that plasma-membrane-bound standard-ferricyanide reductase and nitrate reductase activities of maize roots may be different. A possible regulation of nitrate uptake by plasmalemma redox activity, as proposed by other groups, is discussed.
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PMID:Interaction between electron transport at the plasma membrane and nitrate uptake by maize (Zea mays L.) roots. 1173 41

During photoautotrophic growth under CO2-limited conditions, cells of Synechococcus sp. PCC7942 excreted into the medium about 30% of the nitrite produced by reduction of nitrate. No nitrite was excreted under CO2-sufficient conditions. After transfer of high-CO2-grown cells to CO2-limited conditions, nitrite reductase activity started to decline within 0.5 h and decreased to 50% of the initial level in 3 h, whereas nitrate reductase activity was virtually unchanged. Nitrite started to accumulate in the medium about 3 h after the transfer of the cells to CO2-limited conditions and reached a concentration of >0.4 mM at 17 h. These findings suggested that the nitrite excretion was due to an imbalance of the activities of nitrite reductase and nitrate reductase. Since ammonium, the product of nitrite reduction, was not detected in the medium, it was concluded that the step of nitrite reduction limits the rate of nitrate assimilation under CO2-limited conditions. The extent of decrease in nitrite reductase activity under CO2-limited conditions was much larger than that caused by rifampicin (an inhibitor of RNA synthesis) treatment under high-CO2 conditions. Addition of CO2, in the form of sodium bicarbonate, to the CO2-limited culture increased the nitrite reductase activity, but rifampicin inhibited this increase. These findings suggested the presence of a mechanism that irreversibly inactivates nitrite reductase under CO2-limited conditions.
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PMID:Regulation of Nitrite Reductase Activity under CO2 Limitation in the Cyanobacterium Synechococcus sp. PCC7942. 1222 4

An antisense nitrite reductase (NiR, EC 1.7.7.1) tobacco ( Nicotiana tabacum L.) transformant (clone 271) was used to gain insight into a possible correlation between nitrate reductase (NR, EC 1.6.6.1)-dependent nitrite accumulation and nitric oxide (NO(.)) production, and to assess the regulation of signal transduction in response to stress conditions. Nitrite concentrations of clone 271 leaves were 10-fold, and NO(.) emission rates were 100-fold higher than in wild type leaves. Increased protein tyrosine nitration in clone 271 suggests that high NO(.) production resulted in increased peroxynitrite (ONOO(-)) formation. Tyrosine nitration was also observed in vitro by adding peroxynitrite to leaf extracts. As in mammalian cells, NO(.) and derivatives also increased synthesis of proteins like 14-3-3 and cyclophilins, which are both involved in regulation of activity and stability of enzymes.
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PMID:Nitrite accumulation and nitric oxide emission in relation to cellular signaling in nitrite reductase antisense tobacco. 1224 35

The amino acid modifier phenylglyoxal (PG) gradually inactivated the methyl viologen-coupled nitrate reductase activity of the anoxically grown whole cells of Paracoccus denitrificans. A double log plot of the pseudo-first-order inactivation rate constant versus PG concentration was linear with a mean slope of 1.4 (0.1M sodium phosphate) or 0.87 (0.1M sodium borate). Phenylglyoxalation of cells lowered the limiting velocity (V), while hardly affecting the apparent half-saturation concentration (K(m)) of nitrate. Nitrate afforded no protection against inactivation. The inhibition by PG could be removed by the detergent Triton X-100 or by the lipid-soluble tetraphenylphosphonium countercation, suggesting that PG exerts its effect at the level of nitrate transport. Based on studies with membrane potential- and pH-sensitive fluorescent probes, the inhibition was shown not to be due to changes in the electrochemical gradient of hydrogen ions. Both K(m) and V values for nitrate uptake increased in a hyperbolic fashion in response to exogenously added nitrite. Nitrite promoted a bypass of the inhibition caused by low concentrations of the proton-conducting agent carbonyl cyanide m-chlorophenylhydrazone (CCCP), but was almost ineffective in the case of the PG block. These results are rationalized in terms of two nitrate import pathways that are comparably inhibited by PG and differ in their sensitivities to CCCP. A simplified kinetic model for phenylglyoxalation is proposed to account for the observed nonintegral reaction orders.
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PMID:Inhibition by phenylglyoxal of nitrate transport in Paracoccus denitrificans: a comparison with the effect of a protonophorous uncoupler. 1250 99

Induction, energy gain, effect on growth, and interaction of nitrate and nitrite reduction of Bradyrhizobium sp. (Lupinus) USDA 3045 were characterized. Both nitrate and nitrite were reduced in air, although nitrite reduction was insensitive to ammonium inhibition. Anaerobic reduction of both ions was shown to be linked with energy conservation. A dissimilatory ammonification process was detected, which has not been reported in rhizobia so far. Nevertheless, anaerobic conversion of nitrate to ammonium was lower than 40%, which suggests the presence of an additional, nitrite reductase of denitrifying type. Nitrite toxicity caused a non-linear relationship between biomass produced and >2 mM concentrations of each N oxyanion consumed. At > or =5 mM initial concentrations of nitrate, a stoichiometric nitrite accumulation occurred and nitrite remained in the medium. This suggests an inhibition of nitrite reductase activity by nitrate, presumably due to competition with nitrate reductase for electron donors. Lowering of growth temperature almost completely diminished nitrite accumulation and enabled consumption as high as 10 mM nitrate, which confirms such a conclusion.
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PMID:Aerobic and anaerobic nitrate and nitrite reduction in free-living cells of Bradyrhizobium sp. (Lupinus). 1455 30

The present study shows that when freezing nitrite containing biological samples in the presence of sodium and phosphate, a process of tyrosine nitration and S-nitrosocysteine formation is observed. The underlying mechanism is obviously based on the already described pH decrease in sodium phosphate buffered solutions during the freezing process and probably involves nitrous acid as an intermediate. However, in pure potassium phosphate buffer freeze-artefacts were absent. The yield of 3-nitrotyrosine from albumin-bound or free tyrosine depends not only on the concentration of nitrite, tyrosine or protein, and sodium phosphate but also on the velocity of the freezing process. Nitrite and nitrate were quantified by the Griess/nitrate reductase assay. 3-nitrotyrosine formation was quantitatively measured by HPLC analysis with optical and electrochemical detection as well as qualitatively investigated by immunohistochemistry and slot blot analysis using 3-nitrotyrosine specific antibodies. The formation of S-nitrosocysteine was detected by S-nitrosothiol specific antibodies and quantified by a fluorometric assay. Irrespective of the mechanism and although the here presented results cannot be generalized, the data warrant caution for the analysis of nitration or nitros(yl)ation products following freezing of nitrite containing biological material.
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PMID:A new pitfall in detecting biological end products of nitric oxide-nitration, nitros(yl)ation and nitrite/nitrate artefacts during freezing. 1556 66

Ynt1 is the only high-affinity nitrate uptake system in Hansenula polymorpha. Nitrate uptake was directly correlated with the Ynt1 levels and shown to be independent of nitrate reductase (NR) activity levels. Ynt1 failed to transport chlorate and, as a result, strains lacking YNT1 were sensitive to chlorate, as is the wild-type. Nitrite uptake in a wild-type strain was partially inhibited by nitrate to levels shown by a YNT1-disrupted strain in which, in turn, nitrite transport was not inhibited by nitrate. It is concluded that nitrite uptake takes place by two different transport systems: Ynt1 and a nitrite-specific transporter(s). The nitrite-specific transport system was induced by nitrate; consistently, no induction was observed in strains lacking the transcription factor YNA1, which is involved in nitrate and nitrite induction of the nitrate assimilatory structural genes. Ynt1 presents its optimal rate for nitrite uptake at pH 6, while pH 4 was optimal for the specific nitrite uptake system(s). At pH 5.5, the contribution of Ynt1 to high-affinity nitrate and nitrite uptake was around 95% and 60%, respectively. The apparent Km of Ynt1 for nitrate and nitrite is in the microM range, as is the specific nitrite uptake system for nitrite. The analysis of the effect of the reduced nitrogen sources on nitrate assimilation revealed that glutamine inactivates nitrate and nitrite transport, dependent on Ynt1, but not the nitrite-specific system.
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PMID:The role of Ynt1 in nitrate and nitrite transport in the yeast Hansenula polymorpha. 1496 31

Fluctuations in nitrate reductase activity (NRA), nitrate, nitrite, protein and total nitrogen content of bare-root Scots pine seedlings (Pinus sylvestris L.) raised outdoors were investigated during the first growing season. Nitrate reductase activity was higher in roots than in needles, whereas NO(3) (-) content was higher in needles than in roots and increased in both from June to October. Nitrate reductase activity in roots correlated more closely with NO(3) (-) N in the soil than did NO(3) (-) in the roots. In autumn, there was a closer correlation between foliar NRA and NO(3) (-) in the needles than with NO(3) (-)-N in the soil. Nitrite was not detected in the seedlings during the growing season. Total nitrogen content decreased toward the autumn, whereas protein content initially decreased but increased again in autumn. Acrylic netting placed above the seedlings increased both air and soil temperatures and apparently accelerated the use of nitrate.
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PMID:Nitrate metabolism in Scots pine seedlings during their first growing season. 1497 21

The aim of the present study was to gain further insight on the reliability of the colorimetric determination of the activity of bacterial nitrate reductase to evaluate bacterial concentrations and interaction between microorganisms and enterocyte-like cells. Nitrite produced after incubation of the samples with a nitrate-formate solution was determined with a diazotization reaction with sulphanilic acid and N-naphthyl-ethylene-diamonium dichloride. Cell association assays were performed with differentiated Caco-2 cells. A biphasic relationship was found between nitrite concentration and bacterial densities. This behavior seems to be due to the sigmoideal character of the kinetics of nitrate reduction. Association to Caco-2 cells was strongly strain dependent being Staphylococcus aureus ATCC 25923 the strain showing the highest values of association. For some strains, percentages of association calculated on the basis of the colorimetric assay were significantly higher than those calculated in terms of viable counts. Bacterial association with enterocyte-like cells can be evaluated by measures of the activity of bacterial nitrate reductase provided that the biphasic relationship between bacterial and nitrite concentrations is taken into account for the calculations. Results presented in this paper show the applicability of the colorimetric method to assess the amount of microorganisms associated to human enterocytes in culture.
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PMID:[Evaluation of a colorimetric method for studying the interaction between microorganisms and intestinal epithelial cells]. 1497 70

Excised root systems of tomato plants (early fruiting stage, 2nd flush) were subjected to a gradual transition from normoxia to anoxia by seating the hydroponic root medium while aeration was stopped. Oxygen level in the medium and respiration rate decreased and reached very low values after 12 h of treatment, indicating that the tissues were anoxic thereafter. Nitrate loss from the nutrient solution was strongly stimulated by anoxia (after 26 h) concomitantly with a release of nitrite starting only after 16 h of treatment. This effect was not observed in the absence of roots or in the presence of tungstate, but occurred with whole plants or with sterile in vitro cultured root tissues. These results indicate that biochemical processes in the root involve nitrate reductase. NR activity assayed in tomato roots increased during anoxia. This phenomenon appeared in intact plants and in root tissues of detopped plants. The stimulating effect of oxygen deprivation on nitrate uptake was specific; anoxia simultaneously entailed a release of orthophosphate, sulfate, and potassium by the roots. Anoxia enhanced nitrate reduction by root tissues, and nitrite ions were released into xylem sap and into medium culture. In terms of the overall balance, the amount of nitrite recovered represented only half of the amount of nitrate utilized. Nitrite reduction into nitric oxide and perhaps into nitrogen gas could account for this discrepancy. These results appear to be the first report of an increase in nitrate uptake by plant roots under anoxia of tomato at the early fruiting stage, and the rates of nitrite release in nutrient medium by the asphyxiated roots are the fastest yet reported.
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PMID:Nitrate uptake and nitrite release by tomato roots in response to anoxia. 1531 75


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