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 Collaborative Research Center (CRC) 436 'Metal-Mediated Reactions Modeled after Nature' was founded for the express purpose of analyzing the catalytic principles of metallo-enzymes in order to construct efficient catalysts on a chemical basis. The structure of the active center and neighboring chemical environment in enzymes serves as a focal point for developing reactivity models for the chemical redesign of catalysts. Instead of simply copying enzyme construction, we strive to achieve new chemical intuition based on the results of long-lasting natural evolution. We hope for success, since nature uses a limited set of building blocks, whereas we can apply the full repertoire of chemistry. Key substrates in this approach are small molecules, such as CO2, O2 NO3- and N2. Nature complexes these substrates, activates them and performs chemical transformations--all within the active center of a metalloenzyme. In this article, we report on some aspects and first results of the Collaborative Research Center (CRC) 436, such as nitrate reductase, sphingolipid desaturase, carbonic anhydrase, leucine aminopeptidase and dopamine beta-monooxygenase.
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PMID:Metal-mediated reactions modeled after nature. 1206 95

We characterized three Arabidopsis genes, AtpOMT1, AtpDCT1 and AtpDCT2, localized on chromosome 5 and homologous to spinach chloroplastic 2-oxoglutarate/malate transporter (OMT) gene. The yeast-expressed recombinant AtpOMT1 protein transported malate and 2-oxoglutarate but not glutamate. By contrast, the recombinant AtpDCT1 protein transported 2-oxoglutarate and glutamate at similar affinities in exchange for malate. These findings suggested that AtpOMT1 is OMT and AtpDCT1 is a general dicarboxylate transporter (DCT). The recombinant proteins could also transport oxaloacetate at the same binding sites for dicarboxylates. In particular, the AtpOMT1 had a K(m) value for oxaloacetate one order of magnitude lower than those for malate and 2-oxoglutarate. Although the transcripts for the three genes were accumulated in all tissues examined, the expression of the genes in leaf tissues was light inducible. The expression of the three genes was also induced by nitrate supplement but the induction was most prominent and transient in AtpOMT1 similar to nitrate reductase gene. These findings lead to a proposition that AtpOMT1 functions as an oxaloacetate transporter in the malate-oxaloacetate shuttle across chloroplast membranes. We identified T-DNA insertional mutants of AtpOMT1 and AtpDCT1. Although the AtpOMT1 mutants could grow normally in normal air, the AtpDCT1 mutants were non-viable under the same conditions. The AtpDCT1 mutants were able to grow under the high CO2 condition to suppress photorespiration. These findings suggested that at least AtpDCT1 is a necessary component for photorespiratory nitrogen recycling.
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PMID:Identifying and characterizing plastidic 2-oxoglutarate/malate and dicarboxylate transporters in Arabidopsis thaliana. 1215 33

The activity of nitrate reductase (NR) in leaves is regulated by light and photosynthesis at transcriptional and posttranscriptional levels. To understand the physiological role of these controls, we have investigated the effects of light and CO2 on in vivo NO3- reduction in transgenic plants of Nicotiana plumbaginifolia lacking either transcriptional regulation alone or transcriptional and posttranscriptional regulation of NR. The abolition of both levels of NR regulation did not modify the light/dark changes in exogenous 15NO3- reduction in either intact plants or detached leaves. The same result was obtained for 15N incorporation into free amino acids in leaves after 15NO3- was supplied to the roots, and for reduction of endogenous NO3- after transfer of the plants to an N-deprived solution. In the light, however, deregulation of NR at the posttranscriptional level partially prevented the inhibition of leaf 15NO3- reduction resulting from the removal of CO2 from the atmosphere We concluded from these observations that in our conditions deregulation of NR in the transformants investigated had little impact on the adverse effect of darkness on leaf NO3- reduction, and that posttranscriptional regulation of NR is one of the mechanisms responsible for the short-term coupling between photosynthesis and leaf NO3- reduction in the light.
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PMID:Abolition of Posttranscriptional Regulation of Nitrate Reductase Partially Prevents the Decrease in Leaf NO3- Reduction when Photosynthesis Is Inhibited by CO2 Deprivation, but Not in Darkness. 1222 31

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

The leaves of C(4) plants possess a superior metabolic efficiency not only in terms of photosynthetic carbon assimilation, but also in terms of inorganic nitrogen assimilation, when compared to C(3)plants. In vivo nitrate assimilation efficiency of leaves is dependent on light, but the obligatory presence of light has been debated and its role remains confounded. This problem has not been addressed from the standpoint of the C(3) vs. C(4) nature of the species investigated, which may actually hold the key to resolve the controversy. Here, we present the first report providing evidence for differential photo-regulation of leaf nitrate reduction in barley ( Hordeum vulgare L.) vs. maize ( Zea mays L.) plants, which may help explain the superior nitrogen-use efficiency (and hence superior productivity) of maize plants. The novel finding that carbohydrate-depleted maize leaves were able to reduce nitrate when photosynthesis was inhibited by 3-(3',4'-dichlorophenyl)-1,1'-dimethylurea (DCMU) in the presence of light, raises a very important question about the possibilities of a new photo-regulatory mechanism for supporting nitrate reduction in maize leaves operating independently of photosynthetic carbon dioxide fixation. On the other hand, leaves of barley could not carry out any in vivo nitrate assimilation, whatsoever, under these conditions. We find another fundamental difference between the two species in terms of differential regulation of nitrate reductase (NR; EC 1.6.6.1). In barley leaves, NR activity and activation state remained unaffected due to DCMU, but in sharp contrast, both were appreciably upregulated in maize. Collectively, the results indicate that enzyme capacity is not limiting for nitrate reduction in leaves, as the NR activity was higher in barley than in maize. The maize leaves may have had a selective advantage due to C(4) morphology/metabolism in terms of maintaining a better reductant/carbon skeleton supply for nitrate reduction.
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PMID:DCMU inhibits in vivo nitrate reduction in illuminated barley (C(3)) leaves but not in maize (C(4)): a new mechanism for the role of light? 1224 52

The study on the response of a mutant and a wild-type of Arabidopsis to 660 microliters.L-1 CO2 and ambient CO2 showed that under elevated CO2, the stomatal numbers of the mutant increased, while those of the wild-type decreased. The chlorophyll content and NR (nitrate reductase) activity of the mutant increased, but those of the wild-type had no obvious response. The mutant was not reproductively mature after the continuous exposure to increased CO2 for five months. The results provided evidence of plant response to the changes of atmospheric CO2 concentration, and the clues to related studies on other plants.
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PMID:[Response of an Arabidopsis mutant to elevated CO2 concentration]. 1503 51

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

A total of 1246 Pseudomonas strains were isolated from the rhizosphere of two perennial grasses (Lolium perenne and Molinia coerulea) with different nitrogen requirements. The plants were grown in their native soil under ambient and elevated atmospheric CO2 content (pCO2) at the Swiss FACE (Free Air CO2 Enrichment) facility. Root-, rhizosphere-, and non-rhizospheric soil-associated strains were characterized in terms of their ability to reduce nitrate during an in vitro assay and with respect to the genes encoding the membrane-bound (named NAR) and periplasmic (NAP) nitrate reductases so far described in the genus Pseudomonas. The diversity of corresponding genes was assessed by PCR-RFLP on narG and napA genes, which encode the catalytic subunit of nitrate reductases. The frequency of nitrate-dissimilating strains decreased with root proximity for both plants and was enhanced under elevated pCO2 in the rhizosphere of L. perenne. NAR (54% of strains) as well as NAP (49%) forms were present in nitrate-reducing strains, 15.5% of the 439 strains tested harbouring both genes. The relative proportions of narG and napA detected in Pseudomonas strains were different according to root proximity and for both pCO2 treatments: the NAR form was more abundant close to the root surface and for plants grown under elevated pCO2. Putative denitrifiers harbored mainly the membrane-bound (NAR) form of nitrate reductase. Finally, both narG and napA sequences displayed a high level of diversity. Anyway, this diversity was correlated neither with the root proximity nor with the pCO2 treatment.
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PMID:Frequency and diversity of nitrate reductase genes among nitrate-dissimilating Pseudomonas in the rhizosphere of perennial grasses grown in field conditions. 1565 Sep 15

Understanding of the influences of root-zone CO2 concentration on nitrogen (N) metabolism is limited. The influences of root-zone CO2 concentration on growth, N uptake, N metabolism and the partitioning of root assimilated 14C were determined in tomato (Lycopersicon esculentum). Root, but not leaf, nitrate reductase activity was increased in plants supplied with increased root-zone CO2. Root phosphoenolpyruvate carboxylase activity was lower with NO3(-)- than with NH4(+)-nutrition, and in the latter, was also suppressed by increased root-zone CO2. Increased growth rate in NO3(-)-fed plants with elevated root-zone CO2 concentrations was associated with transfer of root-derived organic acids to the shoot and conversion to carbohydrates. With NH4(+)-fed plants, growth and total N were not altered by elevated root-zone CO2 concentrations, although 14C partitioning to amino acid synthesis was increased. Effects of root-zone CO2 concentration on N uptake and metabolism over longer periods (> 1 d) were probably limited by feedback inhibition. Root-derived organic acids contributed to the carbon budget of the leaves through decarboxylation of the organic acids and photosynthetic refixation of released CO2.
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PMID:The influence of root assimilated inorganic carbon on nitrogen acquisition/assimilation and carbon partitioning. 1572 Jun 30

Effects of atmospheric carbon dioxide enrichment on nitrogen metabolism were studied in barley primary leaves (Hordeum vulgare L. cv. Brant). Seedlings were grown in chambers under ambient (36 Pa) and elevated (100 Pa) carbon dioxide and were fertilized daily with complete nutrient solution providing 12 millimolar nitrate and 2.5 millimolar ammonium. Foliar nitrate and ammonium were 27% and 42% lower (P </= 0.01) in the elevated compared to ambient carbon dioxide treatments, respectively. Enhanced carbon dioxide affected leaf ammonium levels by inhibiting photorespiration. Diurnal variations of total nitrate were not observed in either treatment. Total and Mg(2+)inhibited nitrate reductase activities per gram fresh weight were slightly lower (P </= 0.01) in enhanced compared to ambient carbon dioxide between 8 and 15 DAS. Diurnal variations of total nitrate reductase activity in barley primary leaves were similar in either treatment except between 7 and 10 h of the photoperiod when enzyme activities were decreased (P </= 0.05) by carbon dioxide enrichment. Glutamate was similar and glutamine levels were increased by carbon dioxide enrichment between 8 and 13 DAS. However, both glutamate and glutamine were negatively impacted by elevated carbon dioxide when leaf yellowing was observed 15 and 17 DAS. The above findings showed that carbon dioxide enrichment produced only slight modifications in leaf nitrogen metabolism and that the chlorosis of barley primary leaves observed under enhanced carbon dioxide was probably not attributable to a nutritionally induced nitrogen limitation.
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PMID:Responses of nitrogen metabolism in N-sufficient barley primary leaves to plant growth in elevated atmospheric carbon dioxide. 1622 42


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