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:1.7.1.1 (nitrate reductase)
3,728 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Soybean plants were planted in pots to investigate the effects of soil available silicon on their growth, development and physiological functions. When the content of soil available silicon was 55.1-202.8 mg.kg-1, the protease and lipase activities of germinating seed were increased with increasing soil available silicon content, amylase activity had no obvious change, and the respiration rate of seedlings was accelerated. The bioactivity of seed was increased, but the germination rate had no significant change. The photosynthesis rate, root activity, and nitrate reductase activity of soybean seedlings were enhanced, but the chlorophyll content in leaves had no significant change during seedling growth. The transpiration rate was decreased, while the water utilization efficiency and leaf water content were increased, and the capacity of drought-resistance was promoted. When the available silicon content was > 202.8 mg.kg-1, the abovementioned physiological functions had no significant changes. There was a positively linear relationship between the silicon content in soybean seedlings and the available silicon content in soil (r = 0.994). It could be concluded that the silicon absorbed from soil improved the physiological functions of soybean germinating seed and seedlings. As a result, the seed germination and seedlings growth rate were enhanced.
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PMID:[Effects of soil available silicon on growth, development and physiological functions of soybean]. 1513 91

The enzyme-catalysed reduction of nitrate was studied utilising Aspergillus niger nitrate reductase (NR) and phenosafranin in solution as the enzyme regenerator, working at lower potentials than that of the more common methyl viologen mediator. Cyclic voltammograms when enzyme, phenosafranin and substrate were together put in evidence the enzyme-catalysed reduction of nitrate, although with a relatively slow kinetics. From slope values not dependent on mediator concentration, the apparent Michaelis-Menten constant was evaluated. Analytical parameters for the enzyme-modified electrode in the presence of phenosafranin for the determination of nitrate content in water were assessed, including a recovery assay for nitrate added to a river water sample. The stability of the electrode was checked.
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PMID:An amperometric nitrate reductase-phenosafranin electrode: kinetic aspects and analytical applications. 1521 48

Nitrogen metabolism is not only one of the basic processes of plant physiology, but also one of the important parts of global chemical cycle. Plant nitrogen assimilation directly takes part in the synthesis and conversion of amino acid through the reduction of nitrate. During this stage, some key enzymes, e.g., nitrate reductase (NR), glutamine synthetase (GS), glutamate dehydrogenase (GDH), glutamine synthase (GOGAT), aspargine synthetase (AS), and asparate aminotransferase (AspAT) participate these processes. The protein is assimilated in plant cell through amino acid, and becomes a part of plant organism through modifying, classifying, transporting and storing processes, etc. The nitrogen metabolism is associated with carbonic metabolism through key enzyme regulations and the conversion of products, which consists of basic life process. Among these amino acids in plant cell, glutamic acid (Glu), glutamine (Gln), aspartic acid (Asp) and asparagines (Asn), etc., play a key role, which regulates their conversion each other and their contents in the plant cell through regulating formation and activity of those key enzymes. Environmental factors also affect the conversion and recycle of the key amino acids through regulating gene expression of the key enzymes and their activities. Nitrate and light intensity positively regulate the gene transcription of NR, but ammonium ions and Glu, Gln do the negative way. Water deficit is a very serious constraint on N2 fixation rate and soybean (Glycine max Merr.) grain yield, in which, ureide accumulation and degradation under water deficit appear to be the key issues of feedback mechanism on nitrogen fixation. Water stress decreases NR activity, but increases proteinase activity, and thus, they regulate plant nitrogen metabolism, although there are some different effects among species and cultivars. Water stress also decreases plant tissue protein content, ratio of protein and amino acid, and reduces the absorption of amino acid by plant. On the contrary, soil flooding decreases the content and accumulation amount of root nitrogen in winter wheat by 11.9% from booting to flowering stages and 39.1% during grain filling stage, and reduces the ratio of carbon and nitrogen by 79.6%. The results misadjust the metabolism between carbon and nitrogen, and result in the end of the root growth. Elevated CO2 level could decrease plant leaf nitrogen content under well-watered condition, but almost maintain stable under water deficit condition. The radiation of UV-B significantly reduces the partitioning coefficient and synthetic rate of Rubisco, which significantly decreases the photosynthetic rate. This paper reviewed the pathway of plant nitrogen assimilation, characteristics of key enzymes and their regulating mechanisms with picturing the regulating mode of NR, and described the signal sensing and conduct of plant nitrogen metabolism and the formation, transportation, storage and degradation of plant cell protein with picturing the schedule of protein transport of membrane system in plant cell. Seven key tasks are emphasized in this paper in terms of the review on the effects and mechanisms of key ecological factors including water stress on plant nitrogen metabolism. They are: 1) the absorption mechanism of plant based on different nitrogen sources and environmental regulations, 2) the localization and compartmentalization of the key enzymes of nitrogen mechanism in plant cell, 3) the gene and environmental regulating model and their relationships in various key enzymes of nitrogen metabolism, 4) the function of main cell organs and their responses to environmental factors in nitrogen metabolism process, 5) physiological and chemical mechanism of nitrogen and the relationship between the mechanism and protein formation during crop grain filling, 6) improving gene structure of special species or cultivars using gene engineering methods to enhance the resistance to environmental factor stress and the efficiency of absorption and transportation of nitrogen, and 7) the mechanism of natural nitrogen cycle and its response to human activity disturbance.
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PMID:[Research advance in nitrogen metabolism of plant and its environmental regulation]. 1522 8

The Central Asian Taklamakan desert is characterized by a hyperarid climate with less than 50 mm annual precipitation but a permanent shallow groundwater table. The perched groundwater (2-16 m) could present a reliable and constant source of nitrogen throughout the growing season and help overcome temporal nitrogen limitations that are common in arid environments. We investigated the importance of groundwater and nitrogen fixation in the nitrogen metabolism of desert plants by assessing the possible forms and availability of soil N and atmospheric N and the seasonal variation in concentration as well as isotopic composition of plant N. Water availability was experimentally modified in the desert foreland through simulated flooding to estimate the contribution of surface water and temporally increased soil moisture for nutrient uptake and plant-water relations. The natural vegetation of the Taklamakan desert is dominated by plants with high foliar nitrogen concentrations (2-3% DM) and leaf nitrate reductase activity (NRA) (0.2-1 micromol NO2- g(-1) FW h(-1)). There is little evidence that nitrogen is a limiting resource as all perennial plants exhibited fast rates of growth. The extremely dry soil conditions preclude all but minor contributions of soil N to total plant N so that groundwater is suggested as the dominant source of N with concentrations of 100 microM NO3-. Flood irrigation had little beneficial effect on nitrogen metabolism and growth, further confirming the dependence on groundwater. Nitrogen fixation was determined by the 15N natural abundance method and was a significant component of the N-requirement of the legume Alhagi, the average contribution of biologically fixed nitrogen in Alhagi was 54.8%. But nitrogen fixing plants had little ecological advantage owing to the more or less constant supply of N available from groundwater. From our data we conclude that the perennial species investigated have adapted to the environmental conditions through development of root systems that access groundwater to satisfy demands for both water and nutrients. This is an ecologically favourable strategy since only groundwater is a predictable and stable resource.
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PMID:Nitrogen fixation and metabolism by groundwater-dependent perennial plants in a hyperarid desert. 1537 87

A number of biochemically distinct systems have been characterized for the microbial reduction of the oxyanions, selenate (SeO(4)(2-)) and nitrate (NO(3)(-)). Two classes of molybdenum-dependent nitrate reductase catalyse the respiratory-linked reduction of nitrate (NO(3)(-)) to nitrite (NO(2)(-)). The main respiratory nitrate reductase (NAR) is membrane-anchored, with its active site facing the cytoplasmic compartment. The other enzyme (NAP) is water-soluble and located in the periplasm. In recent years, our understanding of each of these enzyme systems has increased significantly. The crystal structures of both NAR and NAP have now been solved and they provide new insight into the structure, function and evolution of these respiratory complexes. In contrast, our understanding of microbial selenate (SeO(4)(2-)) reduction and respiration is at an early stage; however, similarities to the nitrate reductase systems are emerging. This review will consider some of the common themes and variations between the different classes of nitrate and selenate reductases.
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PMID:Microbial reduction of selenate and nitrate: common themes and variations. 1566 98

Piriformospora indica, an endophytic fungus of the Sebacinaceae family, promotes growth of Arabidopsis and tobacco seedlings and stimulates nitrogen accumulation and the expression of the genes for nitrate reductase and the starch-degrading enzyme glucan-water dikinase (SEX1) in roots. Neither growth promotion nor stimulation of the two enzymes requires heterotrimeric G proteins. P. indica also stimulates the expression of the uidA gene under the control of the Arabidopsis nitrate reductase (Nia2) promoter in transgenic tobacco seedlings. At least two regions (-470/-439 and -103/-89) are important for Nia2 promoter activity in tobacco roots. One of the regions contains an element, ATGATAGATAAT, that binds to a homeodomain transcription factor in vitro. The message for this transcription factor is up-regulated by P. indica. The transcription factor also binds to a CTGATAGATCT segment in the SEX1 promoter in vitro. We propose that the growth-promoting effect initiated by P. indica is accompanied by a co-regulated stimulation of enzymes involved in nitrate and starch metabolisms.
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PMID:The endophytic fungus Piriformospora indica stimulates the expression of nitrate reductase and the starch-degrading enzyme glucan-water dikinase in tobacco and Arabidopsis roots through a homeodomain transcription factor that binds to a conserved motif in their promoters. 1571 Jun 7

Nitrate assimilation in autotrophs provides most of the reduced nitrogen on earth. In eukaryotes, reduction of nitrate to nitrite is catalyzed by the molybdenum-containing NAD(P)H:nitrate reductase (NR; EC 1.7.1.1-3). In addition to the molybdenum center, NR contains iron-heme and flavin adenine dinucleotide as redox cofactors involved in an internal electron transport chain from NAD(P)H to nitrate. Recombinant, catalytically active Pichia angusta nitrate-reducing, molybdenum-containing fragment (NR-Mo) was expressed in P. pastoris and purified. Crystal structures for NR-Mo were determined at 1.7 and 2.6 angstroms. These structures revealed a unique slot for binding nitrate in the active site and identified key Arg and Trp residues potentially involved in nitrate binding. Dimeric NR-Mo is similar in overall structure to sulfite oxidases, with significant differences in the active site. Sulfate bound in the active site caused conformational changes, as compared with the unbound enzyme. Four ordered water molecules located in close proximity to Mo define a nitrate binding site, a penta-coordinated reaction intermediate, and product release. Because yeast NAD(P)H:NR is representative of the family of eukaryotic NR, we propose a general mechanism for nitrate reduction catalysis.
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PMID:Structural basis of eukaryotic nitrate reduction: crystal structures of the nitrate reductase active site. 1577 87

The results showed that when Thellungiella halophila was treated with NaCl, the fresh and dry weight, the water content, the succulency of whole plant and the root/shoot ratio were decreased (Figs. 2-4, 7); the organic matter content in roots was increased and the inorganic matter content in roots was decreased, while those in shoots changed in the opposite direction (Fig. 6); osmotic adjustment ability, the Na+ content, the root activity were increased (Figs. 5, 7, 8); the nitrate reductase activity increased significantly; the O(-)(2*) content decreased at about NaCl 50 mmol/L but increased at about NaCl 100-400 mmol/L (Fig. 10). The micrographs of T. halophila leaf surface by scanning electron microscope (SEM) indicate that there is no salt gland or bladder on the surface of T. halophila (Fig. 1), so it is not a salt-secreting halophyte. The determination of growth parameters, the Na(+) content and Na(+) X-ray (Table 1) microanalysis of T. halophila indicate that T. halophila is not a salt-exclusing halophyte but it probability is a salt-dilution halophyte.
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PMID:[Effects of salt stress on the growth and the nitrate reductase activity in Thellungiella halophila]. 1622 88

Analogue reaction systems of selenate reductase, which reduces substrate in the overall enzymatic reaction SeO4(2-) + 2H+ + 2e- --> SeO3(2-) + H2O, have been developed using bis(dithiolene) complexes of Mo(IV) and W(IV). On the basis of the results of EXAFS analysis of the oxidized and reduced enzyme, the minimal reaction Mo(IV)OH + SeO4(2-) --> Mo(VI)O(OH) + SeO3(2-) is probable. The square pyramidal complexes [M(OMe)(S2C2Me2)2](1-) (M = Mo, W) were prepared as structural analogues of the reduced enzyme site. The systems, [ML(S2C2Me2)2](1-)/SeO4(2-) (L = OMe, OPh, SC6H2-2,4,6-Pr(i)3) in acetonitrile, cleanly reduce selenate to selenite in second-order reactions whose negative entropies of activation implicate associative transition states. Rate constants at 298 K are in the 10(-2)-10(-4) M(-1) s(-1) range with DeltaS++ = -12 to -34 eu. When rate constants are compared with previous data for the reduction of (CH2)4SO, Ph3AsO, and nitrate by oxygen atom transfer, reactivity trends dependent on the metal, axial ligand L, and substrate are identified. As in all other cases of substrate reduction by oxo transfer, the kinetic metal effect k(2)W > k(2)Mo holds. A proposal from primary sequence alignments suggesting that a conserved Asp residue is a likely ligand in the type II enzymes in the DMSO reductase family has been pursued by synthesis of the [Mo(IV)(O2CR)(S2C2Me2)2](1-) (R = Ph, Bu(t)) complexes. The species display symmetrical eta2-carboxylate binding and distorted trigonal prismatic stereochemistry. They serve as possible structural analogues of the reduced sites of nitrate, selenate, and perchlorate reductases under the proposed aspartate coordination. Carboxylate binding has been crystallographically demonstrated for one nitrate reductase, but not for the other two enzymes.
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PMID:Analogue reaction systems of selenate reductase. 1656 54

Previous studies reported that the total flavonoids from the stems and leaves of Scutellaria baicalensis Georgi (TFSS) could enhance and improve learning and memory abilities in experimental animals, and reduce the neuronal pathologic alterations induced by some reagents in mice. The present study examined whether TFSS can improve memory dysfunction, neuronal damage, and abnormal free radicals induced by permanent cerebral ischemia in rats. The permanent cerebral ischemic model in rats was produced by bilateral ligation of the common carotid arteries. The influence of permanent cerebral ischemia on learning and memory was determined in the Morris water maze. The neuronal damage in the hippocampus and cerebral cortex was assessed by the neuronal morphologic observations. The contents of malondialdehyde (MDA) and nitric oxide (NO), and the activities of superoxide dismutase (SOD) and catalase (CAT) in the hippocampus and cerebral cortex were measured using thiobarbituric acid, nitrate reductase, xanthine-xanthine oxidase, and ammonium molybdate spectrophotometric methods, respectively. In learning and memory performance tests, cerebral ischemic rats always required a longer latency time to find the hidden platform and spent a shorter time in the target quadrant in the Morris water maze. TFSS 17.5-70 mg.kg(-1) daily orally administered to ischemic rats for 20 d, from day 16-35 after operation differently reduced the prolonged latency and increased swimming time spent in the target quadrant. In neuronal morphologic observations, daily oral TFSS 17.5-70 mg.kg(-1) for 21 d, from day 16-36 after operation markedly inhibited the ischemia-induced neuronal damage. In addition, the increased contents of MDA and NO, and SOD activity, and the decreased activity of CAT in the hippocampus and cerebral cortex induced by cerebral ischemia were differently reversed. The reference drug piracetam (140 mg.kg(-1) per day for 20-21 d) similarly improved impaired memory and neuronal damage but had no significant effects on free radicals in ligated rats. TFSS can improve memory deficits and neuronal damage in rats after permanent cerebral ischemia, which may be beneficial in the treatment of cerebrovascular dementia.
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PMID:Effects of amelioration of total flavonoids from stems and leaves of Scutellaria baicalensis Georgi on cognitive deficits, neuronal damage and free radicals disorder induced by cerebral ischemia in rats. 1659 23


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