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 ASSIMILATORY NITRATE REDUCTASE (NADH: nitrate oxidoreductase, E.C. 1.6.6.2.) from the marine diatom Thalassiosira pseudonana, Hasle and Heimdal, has been purified 200-fold and characterized. The regulation of nitrate reductase in response to various conditions of nitrogen nutrition has been investigated.Nitrate reductase activity is repressed by the presence of ammonium in vivo, and its synthesis is derepressed when ammonium is absent. The derepression process is sensitive to cycloheximide and apparently requires protein synthesis. Repression of enzyme activity by ammonium is neither inhibited nor delayed by the presence of cycloheximide. In vitro, ammonium does not inhibit enzyme activity.NADH is the physiological electron donor for the enzyme in a flavin-dependent reaction. Spectral studies have indicated the presence of a b-type cytochrome associated with the enzyme. It is possible to observe enzymatic oxidation-reduction reactions which represent partial functions of the over-all electron transport capacity of this enzyme. Nitrate reductase will accept electrons from artificial electron donors such as reduced methyl viologen in a flavin-independent reaction. Further, dithionitereduced flavin adenine dinucleotide can donate electrons to the enzyme to reduce nitrate to nitrite. Finally, the nitrate reductase will exhibit a diaphorase activity and reduce the artificial electron acceptor mammalian cytochrome c in flavin-adeninedinucleotide-dependent reaction.Inhibition studies with potassium cyanide, sodium azide, and o-phenanthroline have yielded indirect evidence for metal component (s) of the enzyme.The inhibition of the NADH-requiring enzyme activities by p-hydroxymercuribenzoate has shown that an essential sulfhydryl group is involved in the initial portion of the electron transport. Heat treatment exerts an effect similar to the p-hydroxymercuribenzoate inhibition; namely, the NADH-requiring activities are rapidly inactivated, whereas the terminal nitrate-reducing activities are relatively stable to heat.The T. pseudonana nitrate reductase molecule has the hydrodynamic properties of an ellipsoid with a frictional coefficient of 1.69 and a molecular weight of 330,000.
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PMID:Purification and Characterization of the Nitrate Reductase from the Diatom Thalassiosira pseudonana. 1665 41

Nitrate reductase (NR)-inactivating proteins from corn roots (Wf-9 x 38-11) and rice cell suspension cultures were tested against a partially purified NR obtained from corn leaves (W64A x W182E). The corn protein was purified 921-fold and the rice protein, 1,660-fold using standard purification procedures. Approximate molecular weight values were 75,000 for the corn protein, and 150,000 for the rice protein as determined by Sephadex G-100 gel filtration. The Sephadex-treated proteins were characterized by electrophoresis on polyacrylamide gels. With a running pH of 9.4 the corn protein remained at the origin whereas the rice protein migrated with an R(F) value of 0.49. With a running pH of 4.0 the corn protein migrated with an R(F) value of 0.25. With the corn protein the activities of NR inactivation and hydrolysis of azocasein were detected in the same protein band. The rice protein, however, had no associated protease activity. From sodium dodecyl sulfate gel electrophoresis, there was one major protein band with an estimated molecular weight of 66,000 in corn protein. In rice protein four bands were observed with estimated molecular weights of 73,000, 66,000, 62,500, and 58,500, respectively.Both inactivators had an inhibitory effect on NADH-NR and NO(3) (-) induced NADH-cytochrome c reductase activities but they had less influence on the activities of FMNH(2)-NR and reduced methylviologen-NR. Inactivation of rice cell NR by rice inactivator was reversed by addition of NADH. Inactivation of corn leaf NR by rice inactivator was inhibited by the simultaneous addition of NADH, but rice inactivator-inactivated corn leaf NR could not be reactivated by NADH.
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PMID:Characteristics of Nitrate Reductase-inactivating Proteins Obtained from Corn Roots and Rice Cell Cultures. 1666 Nov 30

Effects of sodium application on sodium-deficient Amaranthus tricolor L. cv Tricolor seedlings were studied. Thirty-day-old A. tricolor seedlings grown without sodium received either 0.5 millimolar of NaCl or KCl, and the changes in the growth rate, chlorophyll concentration, photosynthetic oxygen evolution, and dark-oxygen consumption, and some enzyme activities were compared. Following the sodium treatment, the sodium concentration in the leaves increased from the initial value of 0.4 millimolar to 2 to 3 millimolar within 24 hours, and also the relative growth rate and O(2) evolution were enhanced within 24 hours. The stimulation of O(2) evolution was greater in the upper leaves than in the lower leaves. Although total chlorophyll concentration did not increase significantly, the increase in the chlorophyll a/b ratio was apparent within 24 hours. There were not significant increases in the C(4) photosynthetic enzyme activities; however, nitrate reductase activity increased by 350% by the sodium treatment within 24 hours, and this increase is considered not to be one of the consequences of the improved photosynthesis. Results suggest that the sodium treatment promoted CO(2) and nitrate assimilation resulting in the growth enhancement, and that sodium can be involved in some other functions than C(4) photosynthesis in A. tricolor plants.
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PMID:Early Responses of Sodium-Deficient Amaranthus tricolor L. Plants to Sodium Application. 1666 82

Because of controversies in the literature on nitric oxide (NO) production by plants, NO detection by the frequently used diaminofluorescein (DAF-2 and DAF-2DA) and by chemiluminescence were compared using the following systems of increasing complexity: (i) dissolved NO gas; (ii) the NO donor sodium nitroprusside (SNP); (iii) purified nitrate reductase (NR); and (iv) tobacco cell suspensions. Low (physiological) concentrations (< or =1 nM) of dissolved NO could be precisely quantified by chemiluminescence, but caused no DAF-2 fluorescence. In contrast to NO gas, SNP, NR, or cell suspensions produced both good DAF fluorescence and chemiluminescence signals which were completely (chemiluminescence) or partly (DAF fluorescence) prevented by NO scavengers. Signal strength ratios between the two methods were variable depending on the NO source, and eventually reflect variable NO oxidation. DAF fluorescence in cell suspension cultures was also increased by an as yet unidentified compound(s) released from cells into the medium. These compounds gave no chemiluminescence signal and were not produced by NR-free mutants. Their production was stimulated by anoxia, by inhibitors of mitochondrial electron transport, and by the fungal elicitor cryptogein. Thus, changes in DAF fluorescence are not necessarily indicative for NO production, but may also reflect NO oxidation and/or production of other DAF-reactive compounds.
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PMID:Nitric oxide (NO) detection by DAF fluorescence and chemiluminescence: a comparison using abiotic and biotic NO sources. 1689 78

The pivotal role of glucose-6-phosphate dehydrogenase (G-6-PDH)-mediated nitric oxide (NO) production in the tolerance to oxidative stress induced by 100 mM NaCl in red kidney bean (Phaseolus vulgaris) roots was investigated. The results show that the G-6-PDH activity was enhanced rapidly in the presence of NaCl and reached a maximum at 100 mM. Western blot analysis indicated that the increase of G-6-PDH activity in the red kidney bean roots under 100 mM NaCl was mainly due to the increased content of the G-6-PDH protein. NO production and nitrate reductase (NR) activity were also induced by 100 mM NaCl. The NO production was reduced by NaN(3) (an NR inhibitor), but not affected by N(omega)-nitro-L-arginine (L-NNA) (an NOS inhibitor). Application of 2.5 mM Na(3)PO(4), an inhibitor of G-6-PDH, blocked the increase of G-6-PDH and NR activity, as well as NO production in red kidney bean roots under 100 mM NaCl. The activities of antioxidant enzymes in red kidney bean roots increased in the presence of 100 mM NaCl or sodium nitroprusside (SNP), an NO donor. The increased activities of all antioxidant enzymes tested at 100 mM NaCl were completely inhibited by 2.5 mM Na(3)PO(4). Based on these results, we conclude that G-6-PDH plays a pivotal role in NR-dependent NO production, and in establishing tolerance of red kidney bean roots to salt stress.
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PMID:Glucose-6-phosphate dehydrogenase plays a pivotal role in nitric oxide-involved defense against oxidative stress under salt stress in red kidney bean roots. 1728 95

Aluminum (Al) is toxic to plants when solubilized into Al(3+) in acidic soils, and becomes a major factor limiting plant growth. However, the primary cause for Al toxicity remains unknown. Nitric oxide (NO) is an important signaling molecule modulating numerous physiological processes in plants. Here, we investigated the role of NO in Al toxicity to Hibiscus moscheutos. Exposure of H. moscheutos to Al(3+) led to a rapid inhibition of root elongation, and the inhibitory effect was alleviated by NO donor sodium nitroprusside (SNP). NO scavenger and inhibitors of NO synthase (NOS) and nitrate reductase had a similar inhibitory effect on root elongation. The inhibition of root elongation by these treatments was ameliorated by SNP. Aluminum inhibited activity of NOS and reduced endogenous NO concentrations. The alleviation of inhibition of root elongation induced by Al, NO scavenger and NOS inhibitor was correlated with endogenous NO concentrations in root apical cells, suggesting that reduction of endogenous NO concentrations resulting from inhibition of NOS activity could underpin Al-induced arrest of root elongation in H. moscheutos.
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PMID:Inhibition of nitric oxide synthase (NOS) underlies aluminum-induced inhibition of root elongation in Hibiscus moscheutos. 1738 95

The severity of Zn deficiency increased with increase in soil exchangeable sodium percentage (ESP) with salt sensitive variety M1-48 scoring 6 at ESP 62 as against only score 3 by salt tolerant variety Pokkali under similar soil conditions. Strikingly, zinc contents were much higher in salt tolerant variety than in salt sensitive one. Zinc application increased zinc concentration in the roots by a factor of 2.85 to 3.87 in Pokkali whereas it rose from 2.37 to 4.35 times in M1-48 depending upon ESP but in the leaves it registered increase of 1.5 to 1.8 times only. In general, the concentrations of reducing sugar were less (about 2.2%) than that of non-reducing (about 3.8%) in both the varieties under normal soil conditions. However, the concentration of reducing sugar doubled (4.2-4.4%) at the highest ESP 62, whereas the concentration of non-reducing sugar though increased (4.1 to 5.1%) but not as vigorously as reducing one. Zinc application reduced the concentration of reducing sugar but not that of non-reducing at similar ESP values. In Pokkali, the concentrations of total sugar increased from 6% at ESP 20 to 9.34% at ESP 62, whereas it registered enhancements of 5.98 to 8.6% in M1-48 under similar conditions. The nitrate reductase (NR) activity decreased with increase in soil sodicity however, the varietal differences in NR activity were wider under Zn-stress than under conditions of applied zinc with Pokkali registering higher NR activities. Carbonic anhydrase activities were higher in salt tolerant variety. Inhibition in carbonic anhydrase activity amounted to 23 and 45% in salt-sensitive variely M1-48 whereas only 19 and 33% in salt-tolerant variety Pokkali at ESP 41 and 62, respectively. The effects of zinc application at higher soil sodicity were more obvious in salt-sensitive variety than in salt-tolerant one. The findings suggest that the tolerance to Zn stress runs parallel to salt tolerance abilities of rice varieties.
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PMID:Metabolic variation in rice cultivars of contrasting salt tolerance and its improvement by zinc in sodic soil. 1740 49

The effects of nitric oxide (NO) and ethylene on Vicia faba L. stomatal movement were studied. The results showed that NO donor SNP (sodium nitroprusside) 10 micromol/L and ethylene 0.04% could induce stomatal closure distinctly and they could promote stomatal closure when treated together. When treated with AVG (an inhibitor of ethylene synthesis), c-PTIO (a specific scavenger of NO) and NaN(3) (an inhibitor of NR), the effects of NO- and ethylene-induced stomatal closure were inhibited but the inhibitor of nitric oxide synthase (NOS) had little effect. We presumed that there was coordinative effect between NO and ethylene in regulation of stomatal closure; ethylene could induce stomatal closure by regulating the production of nitrate reductase (NR)-dependent NO.
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PMID:[The role of nitric oxide in ethylene-induced stomatal closure in Vicia faba L]. 1767 59

Nitrate reductase (NR), a committed enzyme in nitrate assimilation, involves generation of nitric oxide (NO) in plants. Here we show that the NR activity was significantly enhanced by the addition of NO donors sodium nitroprusside (SNP) and NONOate (diethylamine NONOate sodium) to the culturing solution, whereas it was decreased by NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide (cPTIO). Interestingly, both NO gas and SNP directly enhanced but cPTIO inhibited the NR activities of crude enzyme extracts and purified NR enzyme. The cPTIO terminated the interaction between NR-generated NO and the NR itself. Furthermore, the NR protein content was not affected by the SNP treatment. The investigation of the partial reactions catalysed by purified NR using various electron donors and acceptors indicated that the haem and molybdenum centres in NR were the two sites activated by NO. The results suggest that the activation of NR activity by NO is regulated at the post-translational level, probably via a direct interaction mechanism. Accordingly, the concentration of nitrate both in leaves and roots was decreased after 2 weeks of cultivation with SNP. The present study identifies a new mechanism of NR regulation and nitrate assimilation, which provides important new insights into the complex regulation of N-metabolism in plants.
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PMID:Regulation of nitrate reductase by nitric oxide in Chinese cabbage pakchoi (Brassica chinensis L.). 1802 79

Nitric oxide (NO) is a gas displaying multiple physiological functions in plants, animals and bacteria. The enzymes nitrate reductase and NO synthase have been suggested to be involved in the production of NO in plants and algae, but the implication of those enzymes in NO production under physiological conditions remains obscure. Symbiodinium microadriaticum, commonly referred to as zooxanthellae, is a marine microalga commonly found in symbiotic association with a cnidarian host including reef-building corals. Here we demonstrate NO production in zooxanthellae upon supplementation of either sodium nitrite or L-arginine as a substrate. The nitrite-dependent NO production was detected electrochemically and confirmed by the application of 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), a specific NO scavenger. Cells stained with the diaminofluorescein, DAF-2 DA, an NO fluorescent probe, showed an increase in fluorescence intensity upon supplementation of both sodium nitrite and L-arginine. Microscopic observations of DAF-stained cells verified that NO was produced inside the cells. NO production in S. microadriaticum was found to increase upon exposure of cells to an acute heat stress which also caused a decline in the photosynthetic efficiency of PSII (F(v)/F(m)). This study provides substantial evidence to confirm that zooxanthellae can synthesize NO even when they are not in a symbiotic association with a coral host. The increase in NO production at high temperatures suggests that heat stress stimulates the microalgal NO production in a temperature-dependent manner. The implications of these findings are discussed in the light of the coral bleaching phenomenon which is associated with elevated sea surface temperature due to global warming.
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PMID:Heat stress stimulates nitric oxide production in Symbiodinium microadriaticum: a possible linkage between nitric oxide and the coral bleaching phenomenon. 1830 60


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