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)

Soybean (Glycine max L. Merr.) leaves contain two forms of nitrate reductase (NR)-NAD(P)H:NR and NADH:NR. Wild-type (cv Williams), nr(1) mutant and an unrelated cultivar (Prize) were grown with either no N source or with nitrate. Crude extracts were assayed for NR activities and the enzyme forms were purified on blue Sepharose. Analyses were done by polyacrylamide gel electrophoresis and ;Western blotting' using antibodies specific for NR. NAD(P)H:NR was identified as the constitutive NR present in wild-type and Prize, but was absent from the mutant. All three soybean lines contained nitrate-inducible NADH:NR with highest activity at pH 7.5. The results showed that NAD(P)H:NR and constitutive NR were one in the same and confirmed the presence of NADH:NR with pH 7.5 optimum.
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PMID:Immunochemical Characterization of Nitrate Reductase Forms from Wild-Type (cv Williams) and nr(1) Mutant Soybean. 1666 16

The synthesis and accumulation of nitrite has been suggested as a causative factor in the inhibition of legume nodules supplied with nitrate. Plants were grown in sand culture with a moderate level of nitrate (2.1 to 6.4 millimolar) supplied continuously from seed germination to 30 to 50 days after planting. In a comparison of nitrate treatments, a highly significant negative correlation between nitrite concentration in soybean (Glycine max [L.] Merr.) nodules and nodule fresh weight per shoot dry weight was found even when bacteroids lacked nitrate reductase (NR). However, in a comparison of two Rhizobium japonicum strains, there was only 12% as much nitrite in nodules formed by NR(-)R. japonicum as in nodules formed by NR(+)R. japonicum, and growth and acetylene reduction activity of both types of nodules was about equally inhibited. In a comparison of eight other NR(+) and NR(-)R. japonicum strains, and a comparison of G. max, Phaseolus vulgaris, and Pisum sativum, the concentration of nitrite in nodules was unrelated to nodule weight per plant or to specific acetylene reduction activity. The very small concentration of nitrite found in P. vulgaris nodules (0.05 micrograms NO(2) (-)-N per gram fresh weight) was probably below that required for the inhibition of nitrogenase based on published in vitro experiments, and yet the specific acetylene reduction activity was inhibited 83% by nitrate. The overall results do not support the idea that nitrite plays a role in the inhibition of nodule growth and nitrogenase activity by nitrate.
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PMID:Nitrate inhibition of legume nodule growth and activity : I. Long term studies with a continuous supply of nitrate. 1666 51

Soybean plants (Glycine max [L.] Merr) were grown in sand culture with 2 millimolar nitrate for 37 days and then supplied with 15 millimolar nitrate for 7 days. Control plants received 2 millimolar nitrate and 13 millimolar chloride and, after the 7-day treatment period, all plants were supplied with nil nitrate. The temporary treatment with high nitrate inhibited nitrogenase (acetylene reduction) activity by 80% whether or not Rhizobium japonicum bacteroids had nitrate reductase (NR) activity. The pattern of nitrite accumulation in nodules formed by NR(+) rhizobia was inversely related to the decrease and recovery of nitrogenase activity. However, nitrite concentration in nodules formed by NR(-) rhizobia appeared to be too low to explain the inhibition of nitrogenase. Carbohydrate composition was similar in control nodules and nodules receiving 15 millimolar nitrate suggesting that the inhibition of nitrogenase by nitrate was not related to the availability of carbohydrate.Nodules on plants treated with 15 millimolar nitrate contained higher concentrations of amino N and, especially, ureide N than control nodules and, after withdrawal of nitrate, reduced N content of treated and control nodules returned to similar levels. The accumulation of N(2) fixation products in nodules in response to high nitrate treatment was observed with three R. japonicum strains, two NR(+) and one NR(-). The high nitrate treatment did not affect the allantoate/allantoin ratio or the proportion of amino N or ureide N in bacteroids (4%) and cytosol (96%).
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PMID:Nitrate Inhibition of Legume Nodule Growth and Activity : II. Short Term Studies with High Nitrate Supply. 1666 52

The objectives of this study were to determine the effect of light enhancement and hastened reproductive development on nitrogen and dry matter accumulation by field-grown soybean (Glycine max [L.] Merr.). The impacts of photosynthate supply and reproductive development on change in the season-long profiles of in vivo leaf nitrate reductase (NR) activity and root nodule acetylene reduction (AR) activity were evaluated.Light enhancement resulted in significant increases in dry matter accumulation, root nodule fresh weight and AR activity. Seed yield was increased in both light enhanced treatments in 1978 and in one in 1979.Hastened flowering and seed development was accomplished through photoperiod manipulation within a single genotype. Seasonal decline in leaf NR activity was most rapid in plants entering reproductive development early. An early increase in root nodule fresh weight and AR activity was also observed in response to this treatment and was followed similarly by early decline.The addition of high levels of soil-applied nitrogen increased leaf NR activity and delayed late season decline in NR activity for both control and early reproductive plants. Nitrate supply was therefore implicated as limiting to leaf NR activity during the decline associated with flowering and early seed development. A limited additional increase in leaf NR activity was observed in response to light enhancement plus soil-applied nitrogen. As no significant increase in leaf NR activity was observed in response to light enhancement alone, leaf nitrate supply was further implicated as more limiting to leaf NR activity than was photosynthate supply during flowering and early seed development.
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PMID:Effect of multiple factor source-sink manipulation on nitrogen and carbon assimilation by soybean. 1666 8

The objectives of this study were to determine the effect of pod and seed development on leaf chlorophyll concentration, and on activities of leaf ribulose bisphosphate carboxylase, leaf nitrate reductase, and root nodule acetylene reduction in field-grown soybean (Glycine max [L.] Merr.). Two genetic male-sterile lines and their fertile counterparts (Williams and Clark 63) were compared in both 1978 and 1979. Two additional lines (Wells x Beeson and Wells x Corsoy) were compared in 1979.The expression of male-sterile character was nearly complete as very little outcrossing due to insect pollinators was observed. Male-sterile plants showed a delayed late season decline in leaf chlorophyll content and ribulose bisphosphate carboxylase activity when compared with fertile plants. A slight delay in the loss of in vivo leaf nitrate reductase activity was also observed for male-sterile plants. Root nodule fresh weight and acetylene reduction activity declined slightly more rapidly for fertile lines than for male-sterile lines in both years with differences significant on the last two to three sampling dates as leaf loss occurred in the control plants.Seed development was found to increase slightly, the rate of decline of metabolic activity in fertile lines compared with that of male-sterile lines. However, pod development was not an a priori requirement for leaf and root nodule senescence. Male-sterile plants also lost photosynthetic and nitrogen metabolic competence, but at a slower rate. These results support the concept that pod and seed development does not signal monocarpic senescence per se but rather affects the rate at which senescence occurs after flowering.
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PMID:Leaf Nitrate Reductase, d-Ribulose-1,5-bisphosphate Carboxylase, and Root Nodule Development of Genetic Male-Sterile and Fertile Soybean Isolines. 1666 9

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.
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PMID:Nitrate Reductases from Wild-Type and nr(1)-Mutant Soybean (Glycine max [L.] Merr.) Leaves : I. Purification, Kinetics, and Physical Properties. 1666 14

Soybean (Glycine max [L.] Merr.) leaves have been shown to contain three forms of nitrate reductase (NR). Two of the forms, which are present in leaves of wild-type (cv. Williams) plants grown in the absence of NO(3) (-), are termed constitutive and designated c(1)NR and c(2)NR. The third form, which is present in NO(3) (-)-grown mutant (nr(1)) plants lacking the constitutive forms, is termed inducible and designated iNR. Samples of c(1)NR, c(2)NR, and iNR obtained from appropriately treated plants were analyzed for the presence of partial activities, response to inhibitors, and ability to complement a barley NR which lacks the molybdenum cofactor (MoCo) but is otherwise active.The three forms were similar to most assimilatory NR enzymes in that they (a) exhibited NADH-cytochrome c reductase, reduced flavin mononucleotide-NR, and reduced methyl viologen-NR partial activities; (b) were inhibited by p-hydroxymercuribenzoate at the site of initial electron transport through each enzyme; (c) were more inhibited by CN(-) in their reduced enzyme state as compared with their oxidized state; and (d) complemented a MoCo-defective NR (e.g. contained cofactors with characteristics similar to the MoCo found in barley NR and commercial xanthine oxidase). However, among themselves, they showed dissimilarities in their response to treatment with HCO(3) (-) and CN(-), and in their absolute ability to complement the barley NR. The site of effect for these treatments was the terminal cofactor-containing portion of each enzyme. This indicated that, although a terminal cofactor (presumably a MoCo) was present in each form, structural or conformational differences existed in the terminal cofactor-protein complex of each form.
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PMID:Nitrate Reductases from Wild-Type and nr(1)-Mutant Soybean (Glycine max [L.] Merr.) Leaves : II. Partial Activity, Inhibitor, and Complementation Analyses. 1666 11

The objective of this study was to identify factors which limit leaf nitrate reductase (NR) activity as decline occurs during flowering and beginning seed development in soybean (Glycine max [L.] Merr. cv Clark). Level of NR enzyme activity, level of reductant, and availability of NO(3) (-) as substrate were evaluated for field-grown soybean from flowering through leaf senescence. Timing of reproductive development was altered within one genotype by (a) exposure of Clark to an artificially short photoperiod to hasten flowering and podfill, and (b) the use of an early flowering isoline. Nitrogen (N) was soil-applied to selected plots at 500 kilograms per hectare as an additional variable. Stem NO(3) (-) concentration and in vivo leaf NR activity were significantly correlated (R(2) = 0.69 with nitrate in the assay medium and 0.74 without nitrate in the medium at P = 0.001) across six combinations of reproductive and soil N-treatment. The supply of NO(3) (-) from the root to the leaf tissue was the primary limitation to leaf NR activity during flowering and podfill. Levels of NR enzyme and reductant were not limiting to leaf NR activity during this period.
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PMID:Limitations on Leaf Nitrate Reductase Activity during Flowering and Podfill in Soybean. 1666 42

Two nitrate reductase deficient mutants of soybean (Glycine max [L.] Merr. cv Bragg) were isolated from approximately 10,000 M(2) seedlings, using a direct enzymic assay in microtiter plates. Stable inheritance of NR345 and NR328 phenotypes has been demonstrated through to the M(5) generation. Both mutants were affected in constitutive nitrate reductase activity. Assayable activities of cNR in nitrate-free grown seedlings was about 3 to 4% of the control for NR345 and 14 to 16% of the control for NR328. Both mutants expressed inducible NR during early plant development and were sensitive to nitrate and urea inhibition of nodulation. These new mutants will allow an extension of the characterization of nitrate reductases and their function in soybean. Preliminary evidence indicates that NR345 is similar to the previously isolated mutant nr(1), while NR328 is different.
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PMID:Isolation and Initial Characterization of Constitutive Nitrate Reductase-Deficient Mutants NR328 and NR345 of Soybean (Glycine max). 1666 58

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).
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PMID:Biochemical Characterization of Soybean Mutants Lacking Constitutive NADH:Nitrate Reductase. 1666 62


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