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

---

Query: EC:1.7.1.2 (nitrate reductase)
3,861 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Soybean (Glycine max [L.] Merr.) seeds were imbibed and germinated with or without NO(3) (-), tungstate, and norflurazon (San 9789). Norflurazon is a herbicide which causes photobleaching of chlorophyll by inhibiting carotenoid synthesis and which impairs normal chloroplast development. After 3 days in the dark, seedlings were placed in white light to induce extractable nitrate reductase activity. The induction of maximal nitrate reductase activity in greening cotyledons did not require NO(3) (-) and was not inhibited by tungstate. Induction of nitrate reductase activity in norflurazon-treated cotyledons had an absolute requirement for NO(3) (-) and was completely inhibited by tungstate. Nitrate was not detected in seeds or seedlings which had not been treated with NO(3) (-). The optimum pH for cotyledon nitrate reductase activity from norflurazon-treated seedlings was at pH 7.5, and near that for root nitrate reductase activity, whereas the optimum pH for nitrate reductase activity from greening cotyledons was pH 6.5. Induction of root nitrate reductase activity was also inhibited by tungstate and was dependent on the presence of NO(3) (-), further indicating that the isoform of nitrate reductase induced in norflurazon-treated cotyledons is the same or similar to that found in roots. Nitrate reductases with and without a NO(3) (-) requirement for light induction appear to be present in developing leaves. In vivo kinetics (light induction and dark decay rates) and in vitro kinetics (Arrhenius energies of activation and NADH:NADPH specificities) of nitrate reductases with and without a NO(3) (-) requirement for induction were quite different. K(m) values for NO(3) (-) were identical for both nitrate reductases.
...
PMID:Differential light induction of nitrate reductases in greening and photobleached soybean seedlings. 1666 85

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.
...
PMID:Development of Nitrogen Assimilation Enzymes during Photoautotrophic Growth of Chenopodium rubrum Suspension Cultures. 1666 39

NADH:nitrate reductase (EC 1.6.6.1) and NAD(P)H:nitrate reductase (EC 1.6.6.2) were purified from wild-type soybean (Glycine max [L.] Merr., cv Williams) and nr(1)-mutant soybean plants. Purification included Blue Sepharose- and hydroxylapatite-column chromatography using acetone powders from fully expanded unifoliolate leaves as the enzyme source.Two forms of constitutive nitrate reductase were sequentially eluted with NADPH and NADH from Blue Sepharose loaded with extract from wild-type plants grown on urea as sole nitrogen source. The form eluted with NADPH was designated c(1)NR, and the form eluted with NADH was designated c(2)NR. Nitrate-grown nr(1) mutant soybean plants yielded a NADH:nitrate reductase (designated iNR) when Blue Sepharose columns were eluted with NADH; NADPH failed to elute any NR form from Blue Sepharose loaded with this extract. Both c(1)NR and c(2)NR had similar pH optima of 6.5, sedimentation behavior (s(20,w) of 5.5-6.0), and electrophoretic mobility. However, c(1)NR was more active with NADPH than with NADH, while c(2)NR preferred NADH as electron donor. Apparent Michaelis constants for nitrate were 5 millimolar (c(1)NR) and 0.19 millimolar (c(2)NR). The iNR from the mutant had a pH optimum of 7.5, s(20,w) of 7.6, and was less mobile on polyacrylamide gels than c(1)NR and c(2)NR. The iNR preferred NADH over NADPH and had an apparent Michaelis constant of 0.13 millimolar for nitrate.Thus, wild-type soybean contains two forms of constitutive nitrate reductase, both differing in their physical properties from nitrate reductases common in higher plants. The inducible nitrate reductase form present in soybeans, however, appears to be similar to most substrateinduced nitrate reductases found in higher plants.
...
PMID:Nitrate Reductases from Wild-Type and nr(1)-Mutant Soybean (Glycine max [L.] Merr.) Leaves : I. Purification, Kinetics, and Physical Properties. 1666 14

Two nitrate reductase (NR) mutants were selected for low nitrate reductase (LNR) activity by in vivo NR microassays of M(2) seedlings derived from nitrosomethylurea-mutagenized soybean (Glycine max [L.] Merr. cv Williams) seeds. The mutants (LNR-5 and LNR-6) appeared to have normal nitrate-inducible NR activity. Both mutants, however, showed decreased NR activity in vivo and in vitro compared with the wild-type. In vitro FMNH(2)-dependent nitrate reduction and Cyt c reductase activity of nitrate-grown plants, and nitrogenous gas evolution during in vivo NR assays of urea-grown plants, were also decreased in the mutants. The latter observation was due to insufficient generation of nitrite substrate, rather than some inherent difference in enzyme between mutant and wild-type plants. When grown on urea, crude extracts of LNR-5 and LNR-6 lines had similar NADPH:NR activities to that of the wild type, but both mutants had very little NADH:NR activity, relative to the wild type. Blue Sepharose columns loaded with NR extract of urea-grown mutants and sequentially eluted with NADPH and NADH yielded a NADPH:NR peak only, while the wild-type yielded both NADPH: and NADH:NR peaks. Activity profiles confirmed the lack of constitutive NADH:NR in the mutants throughout development. The results provide additional support to our claim that wild-type soybean contains three NR isozymes, namely, constitutive NADPH:NR (c(1)NR), constitutive NADH:NR (c(2)NR), and nitrate-inducible NR (iNR).
...
PMID:Biochemical Characterization of Soybean Mutants Lacking Constitutive NADH:Nitrate Reductase. 1666 62

Chlorella autotrophica, a euryhaline marine alga, and Stichococcus bacillaris, a salt-tolerant soil alga, grow in the presence of methionine sulfoximine (MSX), an inhibitor of glutamine synthetase, by maintaining high levels of NADPH-glutamate dehydrogenase. Nitrate reductase showed no change in MSX-adapted cells. For both species, MSX-adapted cells retained their capacity to accumulate proline in response to salinity, and in S. bacillaris no major shift was observed in the presence of MSX toward the accumulation of sorbitol. Following transfer from 33 to 150% artificial seawater (ASW), both algae exhibited increases in organic solute levels without a lag. Within 6 h of this sudden increase in salinity, the levels of proline in C. autotrophica and of proline and sorbitol in S. bacillaris were similar to those found in steady state 150% ASW cultures. Following transfer from 33 to 150% ASW, S. bacillaris continued [(14)C] bicarbonate photoassimilation at a normal rate and maintained active enzymes of nitrogen assimilation. The incorporation of [(14)C]phenylalanine into proteins was inhibited for about 30 minutes in MSX-free cells and 90 minutes in MSX-adapted cells following transfer from 33 to 150% ASW; the recovery after these lag periods was almost complete.
...
PMID:The Relationship between Inorganic Nitrogen Metabolism and Proline Accumulation in Osmoregulatory Responses of Two Euryhaline Microalgae. 1666 6

A two-step purification protocol was used in an attempt to separate the constitutive NAD(P)H-nitrate reductase [NAD(P)H-NR, pH 6.5; EC 1.6.6.2] activity from the nitric oxide and nitrogen dioxide (NO((x))) evolution activity extracted from soybean (Glycine max [L.] Merr.) leaflets. Both of these activities were eluted with NADPH from Blue Sepharose columns loaded with extracts from either wild-type or LNR-5 and LNR-6 (lack constitutive NADH-NR [pH 6.5]) mutant soybean plants regardless of nutrient growth conditions. Fast protein liquid chromatography-anion exchange (Mono Q column) chromatography following Blue Sepharose affinity chromatography was also unable to separate the two activities. These data provide strong evidence that the constitutive NAD(P)H-NR (pH 6.5) in soybean is the enzyme responsible for NO((x)) formation. The Blue Sepharose-purified soybean enzyme has a pH optimum of 6.75, an apparent K(m) for nitrite of 0.49 millimolar, and an apparent K(m) for NADPH and NADH of 7.2 and 7.4 micromolar, respectively, for the NO((x)) evolution activity. In addition to NAD(P)H, reduced flavin mononucleotide (FMNH(2)) and reduced methyl viologen (MV) can serve as electron donors for NO((x)) evolution activity. The NADPH-, FMNH(2)-, and reduced MV-NO((x)) evolution activities were all inhibited by cyanide. The NADPH activity was also inhibited by p-hydroxymer-curibenzoate, whereas, the FMNH(2) and MV activities were relatively insensitive to inhibition. These data indicate that the terminal molybdenum-containing portion of the enzyme is involved in the reduction of nitrite to NO((x)). NADPH eluted both NR and NO((x)) evolution activities from Blue Sepharose columns loaded with extracts of either nitrate- or zero N-grown winged bean (Psophocarpus tetragonolobus [L.]), whereas NADH did not elute either type of activity. Winged bean appears to contain only one type of NR enzyme that is similar to the constitutive NAD(P)H-NR (pH 6.5) enzyme of soybean.
...
PMID:The Conversion of Nitrite to Nitrogen Oxide(s) by the Constitutive NAD(P)H-Nitrate Reductase Enzyme from Soybean. 1666 14

Nitric oxide (NO) produced from NO synthase(s) (NOS) is an important cell signaling molecule in physiology and pathophysiology. It remains challenging, however, to measure NO accurately and reproducibly in many cell types producing relatively low levels of NO from the enzymes such as endothelial NO synthase (eNOS). In the present study, we describe a very sensitive and convenient analytical method that affords measurement of 1 to 2 nM concentration of NO(x) (nitrite plus nitrate) in culture media. In the present study, we used an ultra-sensitive NO-selective electrochemical sensor (AmiNO700) in combination with a highly efficient nitrate conversion method, which coupled the nitrate reductase step with the glucose-6-phosphate dehydrogenase system. An aliquot of conditioned culture media was first treated with nitrate reductase, NADPH, glucose-6-phosphate dehydrogenase and glucose-6-phosphate to convert nitrate to nitrite quantitatively. The nitrite (that is present originally plus the reduced nitrate) was then reduced to equimolar NO in an acidic iodide bath while NO was being detected by the sensor. With this analytical method, we can quantitatively and reliably measure basal and stimulated NO release from cultured endothelial cells. We believe this improved assay should be useful in measuring a wide range of NO levels, especially the low but physiologically relevant levels, in many cell types.
...
PMID:An improved method to measure nitrate/nitrite with an NO-selective electrochemical sensor. 1705 88

Temperature responses of nitrate reductase (NR) were studied in the psychrophilic unicellular alga, Koliella antarctica, and in the mesophilic species, Chlorella sorokiniana. Enzymes from both species were purified to near homogeneity by Blue Sepharose (Pharmacia, Uppsala, Sweden) affinity chromatography and high-resolution anion-exchange chromatography (MonoQ; Pharmacia; Uppsala, Sweden). Both enzymes have a subunit molecular mass of 100 kDa, and K. antarctica NR has a native molecular mass of 367 kDa. NR from K. antarctica used both NADPH and NADH, whereas NR from C. sorokiniana used NADH only. Both NRs used reduced methyl viologen (MVH) or benzyl viologen (BVH). In crude extracts, maximal NADH and MVH-dependent activities of cryophilic NR were found at 15 and 35 degrees C, respectively, and retained 77 and 62% of maximal activity, respectively, at 10 degrees C. Maximal NADH and MVH-dependent activities of mesophilic NR, however, were found at 25 and 45 degrees C, respectively, with only 33 and 23% of maximal activities being retained at 10 degrees C. In presence of 2 microM flavin adenine dinucleotide (FAD), activities of cryophilic NADH:NR and mesophilic NADH:NR were stable up to 25 and 35 degrees C, respectively. Arrhenius plots constructed with cryophilic and mesophilic MVH:NR rate constants, in both presence or absence of FAD, showed break points at 15 and 25 degrees C, respectively. Essentially, similar results were obtained for purified enzymes and for activities measured in crude extracts. Factors by which the rate increases by raising temperature 10 degrees C (Q10) and apparent activation energy (E(a)) values for NADH and MVH activities measured in enzyme preparations without added FAD differed slightly from those measured with FAD. Overall thermal features of the NADH and MVH activities of the cryophilic NR, including optimal temperatures, heat inactivation (with/without added FAD) and break-point temperature in Arrhenius plots, are all shifted by about 10 degrees C towards lower temperatures than those of the mesophilic enzyme. Transfer of electrons from NADH to nitrate occurs via all three redox centres within NR molecule, whereas transfer from MVH requires Mo-pterin prosthetic group only; therefore, our results strongly suggest that structural modification(s) for cold adaptation affect thermodynamic properties of each of the functional domains within NR holoenzyme in equal measure.
...
PMID:Temperature dependence of nitrate reductase in the psychrophilic unicellular alga Koliella antarctica and the mesophilic alga Chlorella sorokiniana. 1708 Sep 61

Synthesis of silver nanoparticles using alpha-NADPH-dependent nitrate reductase and phytochelatin in vitro has been demonstrated for the first time. The silver ions were reduced in the presence of nitrate reductase, leading to the formation of a stable silver hydrosol 10-25 nm diam. and stabilized by the capping peptide. The nanoparticles were characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy and UV-Vis absorption. These studies will help in designing a rational enzymatic strategy for the synthesis of nanomaterials of different chemical composition, shapes and sizes as well as their separation.
...
PMID:Nitrate reductase-mediated synthesis of silver nanoparticles from AgNO3. 1723 73

Trehalose fulfils a wide variety of functions in cells, acting as a stress protectant, storage carbohydrate and compatible solute. Recent evidence, however, indicates that trehalose metabolism may exert important regulatory roles in the development of multicellular eukaryotes. Here, we show that in the plant pathogenic fungus Magnaporthe grisea trehalose-6-phosphate (T6P) synthase (Tps1) is responsible for regulating the pentose phosphate pathway, intracellular levels of NADPH and fungal virulence. Tps1 integrates glucose-6-phosphate (G6P) metabolism with nitrogen source utilisation, and thereby regulates the activity of nitrate reductase. Activity of Tps1 requires an associated regulator protein Tps3, which is also necessary for pathogenicity. Tps1 controls expression of the nitrogen metabolite repressor gene, NMR1, and is required for expression of virulence-associated genes. Functional analysis of Tps1 indicates that its regulatory functions are associated with binding of G6P, but independent of Tps1 catalytic activity. Taken together, these results demonstrate that Tps1 is a central regulator for integration of carbon and nitrogen metabolism, and plays a pivotal role in the establishment of plant disease.
...
PMID:Tps1 regulates the pentose phosphate pathway, nitrogen metabolism and fungal virulence. 1764 90


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---