Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.7.1.1 (nitrate reductase)
 3,728 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Germinating cotton (Gossypium hirsutum L. cv. Deltapine 16) cotyledons developed two peaks of in vitro nitrate reductase activity; the first was stable in vitro and appeared 24 hours after imbibition; and the second, which was extremely labile in vitro, began to develop after the seedlings had emerged and developed chlorophyll. Nitrite reductase activity peaked only after the seedlings had emerged. Dowex 1-Cl (10%, w/v) and bovine serum albumin (3%, w/v) significantly improved the activity of extracted enzyme; greater improvement occurred as expansion of the cotyledons progressed. The major effect of bovine serum albumin on nitrate reductase activity in cotyledon extracts appeared to be that of making the extracted enzyme more active rather than increasing the amount of nitrate reductase extracted or improving the stability of the extracted enzyme.Attempts to correlate protease activity with the increasingly labile nitrate reductase activity in expanding cotyledons were unsuccessful. Instead, when extracts containing stable nitrate reductase were mixed with extracts containing labile nitrate reductase, the latter was stabilized. The nature of the "protector" in the stable extracts is not known. It is heat-stable, but apparently does not function in vivo since nitrate reductase in germinating cotton seedlings rapidly declines following a peak of activity at 24 hours. We suggest that the protector may function by preventing nitrate reductase from dissociating into inactive subunits.
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PMID:In Vitro Studies of Nitrate Reductase Activity in Cotton Cotyledons: Effects of Dowex 1-Cl and BSA. 1665 29

Protoplasts obtained from expanded leaves of Pisum sativum have been used for the isolation of cell organelles and the subsequent study of the intracellular distribution of the enzymes of nitrate assimilation. The protoplasts were ruptured in a suitable medium and the total lysate subjected to sucrose density gradient centrifugation. Of the total chlorophyll more than 80% was recovered in intact chloroplasts. Nitrite reductase and glutamate synthase were found to be located wholly in the chloroplast. Glutamine synthetase was distributed between the chloroplast and the cytoplasm, with a maximum of 60% of the former. A possible role of the cytoplasmic enzyme is discussed in relation to photorespiration. There was no evidence for the association of nitrate reductase with any cell organelle or membrane fraction.
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PMID:Distribution of the Enzymes of Nitrogen Assimilation within the Pea Leaf Cell. 1666 Jul 3

The nitrite-reducing activity of the normal susceptible biotype of lambsquarters (Chenopodium album L.) was strongly inhibited by atrazine in the assay medium, both in the case of the in vivo assays of leaf discs in light, and in vitro photoreduction assays of crude extracts. In vitro assays of crude extracts with methylviologen or ferredoxin supplying the reducing potential were not inhibited by atrazine. In the resistant biotype, inhibition of nitrite reduction did not occur with any of the above assays. Thus, it appears that atrazine does not inhibit nitrite reductase itself, but rather the availability of photosynthetically supplied electrons for the reduction. Atrazine had no effect when added to the media for either in vivo or in vitro assays of nitrate reduction by either the susceptible or resistant biotype.Young lambsquarters plants were treated with atrazine by spraying the leaves at a rate which was lethal for susceptible plants after 5 or 6 days, but had little effect on the resistant biotype. Nitrite did not accumulate in either biotype, but remained present at the level of about 0.1 microgram nitrite N per gram fresh weight. The nitrate content of susceptible-type leaves did increase to two or three times the initial level, during the first four days after spraying. Usually the only visible effect on the plants during this time was a decreased growth rate. Twenty-four hours after spraying the following activities had fallen to 25% or less of the activities of solvent-sprayed control plants: in vivo nitrite reductase, in vivo nitrate reductase, in vitro NADH-nitrate reductase, in vitro reduced flavin mononucleotidenitrate reductase, and in vitro NADH-diaphorase. In these atrazine-treated plants, in vitro nitrite reductase activity with reducing potential supplied by methylviologen was not affected, nor were any of the above activities in leaves of atrazine-treated resistant plants. The abrupt fall in nitrate reductase represents an effect of atrazine not directly related to inhibition of photosynthesis.
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PMID:Reduction of Nitrate and Nitrite in Lambsquarters (Chenopodium album) Biotypes Resistant and Susceptible to Atrazine Toxicity. 1666 20

A comparative study has been carried out of the growth of two lines of Datura innoxia (Mill.) cells, designated DI-6 and NR1, their resistance to chlorate, and their ability to assimilate nitrate in sterile culture. The NR1 cell line was isolated from DI-6 cultures by first growing the latter in a nitrate-based medium for 5 days and then transferring the cells to a medium containing 2 grams liter(-1) of casein hydrolysate as the sole N source and 49 millimolar KClO(3) for a 6-week incubation period. Cells which survived the chlorate treatment then were transferred to casein hydrolysate medium and have been cultured in the absence of chlorate for more than 18 months (NR1).DI-6 cells can grow in a nitrate-based medium, whereas NR1 cells can take up nitrate but cannot use it as a N source. The inability of NR1 to assimilate nitrate appears to be due to the lack of an active nitrate reductase in these cells. Through the use of a variety of electron donors and acceptors, the lack of nitrate reductase activity in NR1 cells was shown to be due to the absence of, or a defect in, that component of the enzyme which mediates the reduction of nitrate to nitrite.In other experiments, DI-6 and NR1 were grown on a solid medium containing casein hydrolysate (2 grams liter(-1)) as the sole N source. Under these culture conditions, neither cell line contained an active nitrate reductase. The growth on this medium was compared to that on the same medium containing chlorate at concentrations from 0 to 100 millimolar. DI-6 culture growth was inhibited by 70% at a chlorate concentration of 30 micromolar, whereas growth of NR1 was stimulated by more than 60% on the same medium and by 100% at a chlorate concentration of 30 millimolar. In the presence of 100 millimolar chlorate, the growth of both cell lines was completely inhibited. This clear difference between the response of DI-6 and NR1 cells to chlorate even in the absence of nitrate lends support to the observations by others that chlorate inhibits cells by a mechanism other than, or in addition to, its nitrate reductase-catalyzed conversion to chlorite.Nitrite reductase was induced by nitrate in NR1 cells as well as in DI-6. This observation is a further confirmation of the fact that nitrate, not nitrite, is the true inducer of the nitrate assimilatory pathway in higher plants.
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PMID:A Nitrate Reductase-less Variant Isolated from Suspension Cultures of Datura innoxia (Mill.). 1666 93

Experiments were performed to establish a procedure for in vivo measurement of nitrite utilization by leaf tissue of bean (Phaseolus vulgaris L. cv. Top Crop).To measure light-dependent nitrite disappearance, a single disc of leaf tissue was exposed to light for 1 hour at 30 C while immersed in incubation medium (approximately 0.11 milliliter per square centimeter of leaf area) in the bottom of a tall-form glass beaker. The incubation medium was 100 millimolar phosphate buffer (pH 7.5) with added wetting agent and nitrite. The wetting agent combination of 1% 1-propanol plus 0.05% Neutronyx-600 was used in some experiments for compatibility with established in vivo nitrate reductase (NR) assays; however, 0.05% Neutronyx-600 alone was found to be a suitable substitute. Parallel assays run in the dark on related tissue are recommended as a means to determine the amount of nitrite synthesized within the tissue by the NR system. Adding the results of the two assays gives an estimate of total nitrite utilization by the leaf tissue. It was found that 20 millimolar nitrite in the incubation medium was the most suitable level of external nitrite for promoting light-dependent nitrite disappearance. This was also found to reduce, sometimes to zero, the rate of synthesis of nitrite by NR. NR activity declined steadily with advancing age. Except for very young tissue, the rate of nitrite disappearance was independent of age. Nitrite disappearance was completely blocked by diuron.
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PMID:In Vivo Nitrite Reduction in Leaf Tissue of Phaseolus vulgaris L. 1666 53

1. Possible mechanisms regulating the activities of three enzymes involved in nitrate assimilation, nitrate reductase, nitrite reductase and glutamate dehydrogenase, were studied in radish cotyledons. 2. Nitrate-reductase and nitrite-reductase activities are low in nitrogen-deficient cotyledons, and are induced by their substrates. 3. Glutamate dehydrogenase is present regardless of the nitrogen status, and the enzyme can be increased only slightly by long-term growth on ammonia. 4. Although nitrate is the best inducer of nitrate reductase, lower levels of induction are also obtained with nitrite and ammonia. The experiments did not distinguish between direct or indirect induction by these two molecules. 5. Nitrite reductase is induced by nitrite and only indirectly by nitrate. 6. The induction of both nitrate reductase and nitrite reductase is prevented by the inhibitors actinomycin D, puromycin and cycloheximide, indicating a requirement for the synthesis of RNA and protein. 7. The decay of nitrate reductase, determined after inhibition of protein synthesis, is slower than the synthesis of the enzyme. Nitrite reductase is much more stable than nitrate reductase. 8. The synthesis of nitrate reductase is not repressed by ammonia, but is repressed by growth on a nitrite medium. 9. There is no inhibition of nitrate reductase, nitrite reductase or glutamate dehydrogenase by the normal end products of assimilation, but cyanate is a fairly specific inhibitor of nitrate reductase.
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PMID:The regulation of activity of the enzymes involved in the assimilation of nitrate by higher plants. 1674 12

Desulfovibrio desulfuricans ATCC 27774 is a sulfate reducer that can adapt to nitrate respiration, inducing the enzymes required to utilize this alternative metabolic pathway. Nitrite reductase from this organism has been previously isolated and characterized, but no information was available on the enzyme involved in the reduction of nitrate. This is the first report of purification to homogeneity of a nitrate reductase from a sulfate reducing organism, thus completing the enzymatic system required to convert nitrate (through nitrite) to ammonia. D. desulfuricans nitrate reductase is a monomeric (circa 70 kDa) periplasmic enzyme with a specific activity of 5.4 K(m) for nitrate was estimated to be 20 microM. EPR signals due to one [4Fe-4S] cluster and Mo(V) were identified in dithionite reduced samples and in the presence of nitrate.
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PMID:Isolation and preliminary characterization of a soluble nitrate reductase from the sulfate reducing organism Desulfovibrio desulfuricans ATCC 27774. 1688 8

Tomato plants (Lycopersicon esculentum Mill, cv. Chibli F1) grown for 10 days on control medium were exposed to differing concentrations of NaCl (0, 25, 50, and 100mM). Increasing salinity led to a decrease of dry weight (DW) production and protein contents in the leaves and roots. Conversely, the root to shoot (R/S) DW ratio was increased by salinity. Na(+) and Cl(-) accumulation were correlated with a decline of K(+) and NO(3)(-) in the leaves and roots. Under salinity, the activities of nitrate reductase (NR, EC 1.6.6.1) and glutamine synthetase (GS, EC 6.3.1.2) were repressed in the leaves, while they were enhanced in the roots. Nitrite reductase (NiR, EC 1.7.7.1) activity was decreased in both the leaves and roots. Deaminating activity of glutamate dehydrogenase (GDH, EC 1.4.1.2) was inhibited, whereas the aminating function was significantly stimulated by salinity in the leaves and roots. At a high salt concentration, the nicotinamide adenine dinucleotide reduced (NADH)-GDH activity was stimulated concomitantly with the increasing NH(4)(+) contents and proteolysis activity in the leaves and roots. With respect to salt stress, the distinct sensitivity of the enzymes involved in nitrogen assimilation is discussed.
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PMID:NaCl stress effects on enzymes involved in nitrogen assimilation pathway in tomato "Lycopersicon esculentum" seedlings. 1712 28

Anaerobic induction of nitrate reductase in subcellular fractions of Bradyrhizobium sp. strain USDA 3045 showed fivefold increase of the enzyme activity in spheroplasts, considered as the source of intact-membrane-bound nitrate reductase, within a 3 h time frame after nitrate addition. Such a dynamics was confirmed at the protein level, with antibodies specific to membrane-bound nitrate reductase. Nitrate reductase activity in the periplasm was one order of magnitude lower and significant only at initial 3 h of induction, within a narrow range of nitrate added. Nitrite induced the membrane-bound nitrate reductase at least 70% as effectively as nitrate, as judged from its activity pattern and Western blot analysis. The limited ability of Bradyrhizobium sp. to dissimilate > or =5 mM nitrate is not due to direct inhibition of respiratory nitrate reductase by accumulated nitrite. Moreover, a synergistic induction of membrane-bound nitrate reductase by nitrate and nitrite was indicated due to a twofold higher protein synthesis after simultaneous addition of these N oxyanions than when they were given separately.
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PMID:Effect of N oxyanions on anaerobic induction of nitrate reductase in subcellular fractions of Bradyrhizobium sp. (Lupinus). 1911 69

The nitrate-nitrite-NO pathway is emerging as an alternative to the l-arginine/NO-synthase pathway for the generation of NO in mammals. Bioactivation of the stable nitrate anion involves initial reduction to nitrite by commensal bacteria in the gastrointestinal tract. Nitrite is then further metabolized in blood and tissues to form nitric oxide (NO) and other bioactive nitrogen oxides. In addition to nitrate reduction by bacteria, a functional mammalian nitrate reductase activity was recently explored. It was demonstrated that xanthine oxidoreductase (XOR) and possibly other enzymes can catalyze nitrate reduction under normoxic conditions in vivo. In the present study, we compared nitrate reduction in germ free (GF) and conventional mice. One aim was to see if the complete lack of bacterial nitrate reduction in the GF mice would be associated with an upregulation of mammalian nitrate reductase activity. Sodium nitrate (NaNO(3)) or placebo (NaCl) was injected intraperitoneally and blood and tissues were collected 1.5-2h later for measurements of nitrate and nitrite and in some cases analyses of protein expression. Tissue and plasma levels of nitrate increased to a similar extent in conventional and GF animals after nitrate administration. Plasma nitrite was 3-fold higher in GF mice receiving nitrate compared to placebo while this effect of nitrate was absent in the conventional mice. In GF mice pretreated with the xanthine oxidase inhibitor allopurinol the increase in nitrite was attenuated. The levels of nitrite in the liver and small intestine increased after the nitrate load in GF mice but not in the conventional mice. Anaerobic nitrate reduction to nitrite in intestinal tissue homogenates was also accelerated in GF mice. Studies of tissue protein levels revealed increased expression of XOR in the livers of GF animals. We conclude that XOR expression in tissues is enhanced in germ free mice and this may explain the apparently greater tissue nitrate reductase activity observed in these animals. Future studies will reveal if this represents a compensatory functional response to uphold nitrite homeostasis in the absence of commensal bacteria.
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PMID:Enhanced xanthine oxidoreductase expression and tissue nitrate reduction in germ free mice. 2014 47


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