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 localization of enzymes responsible for nitrate assimilation and the generation of NADH for nitrate reduction were studied in corn (Zea mays L.) leaf blades. The techniques used effectively separated mesophyll and bundle sheath cells as judged by microscopic observations, enzymic assays, chlorophyll a/b ratios and photochemical activities. Nitrate reductase, nitrite reductase, and the nitrate content of leaf blades were localized primarily in the mesophyll cells, although some nitrite reductase was found in the bundle sheath cells. Glutamine synthetase, NAD-malate dehydrogenase, NAD-glyceraldehyde-3-phosphate dehydrogenase, and NADP-glutamate dehydrogenase were found in both types of cells, however, more NADP-glutamate dehydrogenase was found in the bundle sheath cells than in the mesophyll cells. These data indicate that the mesophyll cells are the major site for nitrate assimilation in the leaf blade because they contained an ample supply of nitrate and the enzymes considered essential for the assimilation of nitrate into amino acids. Because the specific activity of nitrate reductase was severalfold lower than the other enzymes involved in nitrate assimilation, nitrate reduction is indicated as the rate-limiting step in situ. A sequence of reactions is proposed for nitrate assimilation in the mesophyll cells of corn leaves as related to the C-4 pathway of photosynthesis.
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PMID:Pathway for Nitrate Assimilation in Corn (Zea mays L.) Leaves: Cellular Distribution of Enzymes and Energy Sources for Nitrate Reduction. 1666 May 71

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 effects of thioredoxin, dithioerythrol, and mixtures of both on enzymes involved in N metabolism of Chlorella sorokiniana have been studied. Glutamine synthetase, inactivated in vivo, was activated 8-fold by thioredoxin and dithioerythrol. By the same treatment, the activity of glutamate synthase was stimulated nearly 4-fold. Thus, two key enzymes of N metabolism were shown to be regulated via thioredoxin. The enzymes of the nitrate reducing system, i.e. nitrate reductase and nitrite reductase, were not affected by thiols. From these results, a model of NO(3) (-) metabolism is put forward which considers the regulating effect of light.
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PMID:A Thioredoxin-Mediated Activation of Glutamine Synthetase and Glutamate Synthase in Synchronous Chlorella sorokiniana. 1666 28

Chenopodium rubrum cells were grown in suspension as a photoautotrophic culture with a 16 hour day. Cell growth had three phases: a 3-day lag, a 3-week logarithmic phase, and a 10-day stationary phase. Chlorophyll content increased steadily during log phase and reached a level of 0.5 to 0.6 mg Chl g(-1) fresh weight. Soluble protein of the cells increased more rapidly from day 4 to day 12 than during midlog phase. Initially, ammonium was taken up in preference to nitrate. However, during the second two weeks of growth, ammonium and nitrate were taken up simultaneously; this period of growth was the time of highest rates of N uptake by the cultured cells. Glutamine synthetase had a high specific activity (17 mumol.hour(-1) mg(-1) protein) in day 1 cells, and this level was sustained until midlog phase when it increased by 20%. Methyl viologen-dependent glutamate synthase specific activity increased rapidly in lag phase cells (day 4 = 10 mumol.hour(-1) mg(-1) protein), but decreased by day 9 to about 50% of the peak and remained constant. NADH:nitrate reductase specific activity increased rapidly in lag phase cells and reached a plateau that lasted from day 4 to 14 (1 mumol.hour(-1) mg(-1) protein). Methyl viologen-dependent nitrite reductase specific activity was high when assayed on day 5 and increased to a maximum on day 15 to 16 (12 mumol.hour(-1) mg(-1) protein). NADPH- and NADH-dependent glutamate dehydrogenase specific activities remained rather constant throughout the growth cycle. The cells appeared to have developed photosynthetic competence and to have leaf-like activities of nitrogen assimilation enzymes.
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PMID:Development of Nitrogen Assimilation Enzymes during Photoautotrophic Growth of Chenopodium rubrum Suspension Cultures. 1666 39

Infection by the fungal endophyte Acremonium coenophialum affected the accumulation of inorganic and organic N in leaf blades and leaf sheaths of KY 31 tall fescue (Festuca arundinacea Schreb.) grown under greenhouse conditions. Total soluble amino acid concentrations were increased in either the blade or sheath of the leaf from infected plants. A number of amino acids were significantly increased in the sheath, but only asparagine increased in the blade. Infection resulted in higher sheath NH(4) (+) concentrations, whereas NO(3) (-) concentrations decreased in both leaf parts. The effects on amino acid, NO(3) (-), and NH(4) (+) concentrations were dependent upon the level of N fertilization and were usually apparent only at the high rate (10 millimolar) of application. Administration of (14)CO(2) to the leaf blades increased the accumulation of (14)C in their amino acid fraction but not in the sheaths of infected plants. This may indicate that infection increased amino acid synthesis in the blade but that translocation to the sheath, which is the site of fungal colonization, was not affected. Glutamine synthetase activity was greater in leaf blades of infected plants at high and low N rates of fertilization, but nitrate reductase activity was not affected in either part of the leaf. Increased activities of glutamine synthetase together with the other observed changes in N accumulation and metabolism in endophyte-infected tall fescue suggest that NH(4) (+) reassimilation could also be affected in the leaf blade.
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PMID:Effects of the Fungal Endophyte Acremonium coenophialum on Nitrogen Accumulation and Metabolism in Tall Fescue. 1666 41

We studied the salt stress (100 mM NaCl) effects on the diurnal changes in N metabolism enzymes in tomato seedlings (Lycopersicon esculentum Mill. cv. Chibli F1) that were grown under high nitrogen (HN, 5 mM NO(3)(-)) or low nitrogen (LN, 0.1 mM NO(3)(-)). NaCl stress led to a decrease in plant DW production and leaf surface to higher extent in HN than in LN plants. Total leaf chlorophyll (Chl) content was decreased by salinity in HN plants, but unchanged in LN plants. Soluble protein content was decreased by salt in the leaves from HN and LN plants, but increased in the stems-petioles from LN plants. Nitrate reductase (NR, EC 1.6.1.6) showed an activity peak during first part of the light period, but no diurnal changes were observed for the nitrite reductase (NiR, EC 1.7.7.1) activity. Glutamine synthetase (GS, EC 6.3.1.2) and glutamate synthase (Fd-GOGAT, EC 1.4.7.1) activities increased in HN plant leaves during the second part of the light period, probably when enough ammonium is produced by nitrate reduction. NR and NiR activities in the leaves were more decreased by NaCl in LN than in HN plants, whereas the opposite response was obtained for the GS activity. Fd-GOGAT activity was inhibited by NaCl in HN plant leaves, while salinity did not shift the peak of the NR and Fd-GOGAT activities during a diurnal cycle. The induction by NaCl stress occurred for the NR and GS activities in the roots of both HN and LN plants. Glutamate dehydrogenase (GDH, EC 1.4.1.2) activity shifted from the deaminating activity to the aminating activity in all tissues of HN plants. In LN plants, both aminating and deaminating activities were increased by salinity in the leaves and roots. The differences in the sensitivity to NaCl between HN and LN plants are discussed in relation to the N metabolism status brought on by salt stress.
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PMID:Salinity-induced tissue-specific diurnal changes in nitrogen assimilatory enzymes in tomato seedlings grown under high or low nitrate medium. 1688 71

Tobacco (Nicotiana Tabaccum, Bureley v. Fb9) seedlings were grown for 30 days on control medium, and then treated for seven days with different concentrations (0, 10, 20, 50 and 100 muM) of CdCl(2). Cadmium (Cd) was mostly accumulated in the leaves. However, nitrate reductase and nitrite reductase activities (NR, EC 1.6.1.6 and NiR, EC 1.7.7.1) were more inhibited by Cd stress in the roots than in leaves. Glutamine synthetase activity (GS, EC 6.3.1.2) was inhibited by Cd treatment in roots and leaves. In both organs, aminating activity of glutamate dehydrogenase (GDH, EC 1.4.1.2) and protease activity were significantly stimulated in the leaves and roots of stressed plants. The lesser extents of Cd stress effects on leaves, despite their high Cd accumulation, suggest that: (i) tobacco leaves may evolve adaptive process to partially inactivate Cd ions; and (ii) tobacco is useful for phytoremediation.
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PMID:Tissue-specific cadmium accumulation and its effects on nitrogen metabolism in tobacco (Nicotiana tabaccum, Bureley v. Fb9). 1920 Sep 27

Glutamine synthetase activity in the ascomycete fungus Aspergillus nidulans is regulated by nitrogen source. The lowest activities are obtained when the fungus is grown on L-glutamine, and the highest activities when grown on L-glutamate + arabinose. Glutamine auxotrophs of the fungus have been isolated, and one of these mutant strains, glnA-1, has been shown to lack the enzyme glutamine synthetase. The mutation is recessive, and is located on the right arm of chromosome II. In addition to abolishing glutamine synthetase activity, the mutation results in the relief of repression for several enzyme activities normally subject to repression by ammonium. These include nitrate reductase, asparaginase, proline uptake and urea uptake.
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PMID:A single mutation leads to loss of glutamine synthetase and relief of ammonium repression in Aspergillus. 2418 46

Nitrate and nitrite reductases were both induced by adding three concentrations of nitrate to the nutrient supply of nitrate-starved barley seedlings. Enzyme induction was not proportional to the amount of nitrate introduced. Glutamine synthetase also increased above a high endogenous activity but the increase did not differ significantly between any of the three nitrate treatments. Nitrate accumulated rapidly in leaves of plants given 4.0 mM or 0.5 mM nitrate but not with 0.1 mM nitrate. In all treatments, amino acids in leaves increased for 2 d, chiefly attributable to glutamine, then declined. Transferring plants from the three nitrate treatments to nitrate-free nutrient produced an immediate decline in nitrate reductase but nitrite reductase continued to increase for 2 d, before declining. Glutamine-synthetase activity was not affected by withdrawal of nitrate, nor did nitrate withdrawal retard plant growth during the 9-d period of the experiment. The disparity between accumulated nitrate and nitrate-reducing capacity and the rapid decrease in leaf nitrate when nutrient nitrate supply was removed, indicated the presence of a nitrate-storage pool that could be called upon to maintain amino-acid production in times of nitrogen starvation.
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PMID:Some effects of nitrate abundance and starvation on metabolism and accumulation of nitrogen in barley (Hordeum vulgare L. cv Sonja). 2425 30

The taxonomic affinity of Cyanophora paradoxa and its endosymbiotically living cyanelles has not yet been resolved. In the present communication, the enzymes of assimilatory nitrate reduction are investigated in cell-free preparations from the cyanelles and from the eukaryotic host. Nitrate reductase of Cyanophora is a NADH-dependent, soluble enzyme, occurring only in the protoplasm of the eukaryotic host. In contrast, nitrite reductase is ferredoxin-dependent and bound to the thylakoids of cyanelles. Glutamine synthetase and ferredoxin-dependent glutamate synthase (GOGAT) are present both in cyanelles and the eukaryote. Activity levels of alanine dehydrogenase and glutamic acid dehydrogenase are marginal in Cyanopnora, indicating that ammonia is suggest assimilated by the glutamine synthetase GOGAT pathway. The data also that NH 4 (+) leaves the cyanelles to meet the nitrogen requirements of the eukaryote. It is concluded that the pathway of assimilatory nitrate reduction is similar in Cyanophora and photosynthetic eukaryotic cells and is different from that in byanobacteria.
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PMID:Metabolic activities in Cyanophora paradoxa and its cyanelles : I. The enzymes of assimilatory nitrate reduction. 2427 17


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