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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)

Effect of nitrate on the nitrogenase (C2H2-reduction) activity, growth of nodule tissue accumulation of nitrate and nitrate reductase activity in 4-weeks-old nodulated peas (Pisum sativum L.) was investigated. A relatively slow decrease of the total nitrogenase activity (mumol C2H4 per root per h), as compared with plants cultivated without nitrate, was due to both retardation of further growth of the nodule tissue and to a decrease of their specific nitrogenase activity (mumol C2H4 per gf.wt. per h). However, an absolute and pronounced decrease of both nitrogenase activities occurred only 4 or 7 d after the application of nitrate. The addition of nitrate led to its rapid accumulation in the nodule and leaf tissue with a simultaneous induction of the nitrate reductase activity. The nitrogenase activity was not completely inhibited even after a 7-d cultivation with 280 m NO3- -N in the nutrient medium and after accumulation of up to 180 ppm NO3- -Nf.wt. in the nodule tissue. The results obtained indicate that the "photosynthate deprivation" reflects competition between assimilation of nitrate and fixation of dinitrogen.
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PMID:Symbiotic dinitrogen fixation as affected by short-term application of nitrate to nodulated Pisum sativum L. 692 72

A Pseudomonas sp. isolated from crude oil reduced ferric ions (Fe(III)) to ferrous ions (Fe(II)). In the presence of nitrate (NO3-) after prolonged incubation, the amount of Fe(II) was lower than in its absence. However, during short incubation periods, the presence of NO3- significantly increased (99.5% confidence limit) the amount of Fe(II) produced. The decrease in Fe(II) on prolonged incubation was associated with increased production and accumulation of nitrite (NO2-). Under low NO3- levels, where the production of NO2- was limited, a decrease in NO2- concentration was accompanied by an increase in Fe(II) production to levels comparable with those obtained in the absence of NO3-. Preinduction of cells for nitrate reductase, which favoured rapid NO2- production, resulted in a more rapid decrease in Fe(II) production than in cells that were not preinduced. It is proposed that the inhibitory effect of NO3- on microbial reduction of Fe(III) is due to a secondary reaction, which involves the chemical oxidation of Fe(II) by NO2-.
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PMID:Effect of nitrate on reduction of ferric iron by a bacterium isolated from crude oil. 719 77

An assay for the simultaneous measurement of nitrite and nitrate, products of nitric oxide metabolism, is described. Others have reported pretreating sample by using nitrate reductase (NR) and NADPH to reduce endogenous NO3- before assaying the resultant NO2- using the Griess reaction. However, we found that the NADP+ formed during pretreatment interfered with the Griess reaction when NADPH was used at concentrations necessary to drive the NR reaction. For instance, 500 microM NADP+ in 100 microM NaNO3- (without NR) causes a 90% interference with the formation of Griess reaction product. To limit interference, we modified the method by decreasing the NADPH concentration to 1 microM. NADPH was regenerated by coupling the NR reaction with that catalyzed by glucose-6-phosphate dehydrogenase (GD). Using this method, NaNO3- standard curves were linear up to 100 microM and coincided with control curves obtained using NaNO2- incubated in parallel. Addition of urine up to a strength of 20% did not interfere with the assay. Comparison with an alternative assay based on cadmium reduction resulted in the following linear regression: [Cd method] = 0.915*[NR-GD method] + 0.37, r2 = 0.997. Coupling GD to NR to recycle NADPH allows this cofactor to be used at a low concentration so that interference with the Griess reaction is negligible.
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PMID:Sample pretreatment with nitrate reductase and glucose-6-phosphate dehydrogenase quantitatively reduces nitrate while avoiding interference by NADP+ when the Griess reaction is used to assay for nitrite. 773 51

Assimilatory nitrate reductase from Chlorella vulgaris catalyzes the rate-limiting step, the conversion of nitrate to nitrite, in nitrate assimilation. Initial rate studies of nitrate reductase activity, performed under optimum conditions of constant ionic strength (mu = 0.2) and pH (8.0) and using NADH as reductant, indicated the absence of substrate inhibition at NADH concentrations below 300 microM and NO3- concentrations less than 3 mM. Chlorella nitrate reductase exhibited a marked preference for NADH (Vmax = 9.2 mumol NADH/min/nmol heme and Km = 2.3 microM) as the physiological electron donor but could also utilize alpha-NADH (Vmax = 5.6 mumol NADH/min/nmol heme and Km = 131 microM) and NADPH (Vmax = 0.6 mumol NADPH/min/nmol heme and Km = 910 microM) though with significantly decreased efficiency. Examination of various NADH-analogs indicated that reduced nicotinamide hypoxanthine dinucleotide (NHDH) was used most efficiently (Vmax = 9.3 mumol NHDH/min/nmol heme and Km = 7.9 microM), while reduced nicotinamide mononucleotide (NMNH) was utilized least efficiently (Vmax = 0.07 mumol NMNH/min/nmol heme and Km = 676 microM). Overall, modifications to the nicotinamide moiety or the addition of a phosphate group were observed to result in the most significant decreases in Vmax, indicating poor reducing substrates. Product inhibition studies indicated both NAD+ (Ki = 2.2 mM) and NADP+ (Ki = 10.5 mM) to be competitive inhibitors of Chlorella NR. A variety of NAD+ analogs were also determined to act as competitive inhibitors with varying degrees of efficiency. 3-Pyridinealdehyde adenine dinucleotide was the most efficient inhibitor (Ki = 0.74 mM) while nicotinamide was the least efficient (Ki = 18.1 mM). Overall, changing substituents on the nicotinamide ring or its complete deletion produced the most effective inhibitors compared to NAD+. In contrast, changes in the adenine or ribose moieties produced less effective inhibitors when compared to NAD+. These results represent the most comprehensive analysis of the effect of modifications of the physiological reductant (NADH) and product (NAD+) on nitrate reductase activity.
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PMID:Assimilatory nitrate reductase: reduction and inhibition by NADH/NAD+ analogs. 797 4

A pH dependent reduction in growth, pigment, ATP content, O2- evolution, carbon fixation, photosynthetic electron transport system, nutrient uptake (NO3- and NH4+), nitrate reductase, and ATPase activities and increase in K+ efflux of Chlorella vulgaris was noticed following supplementation of Cu and Ni to the culture medium. PS II was found to be more sensitive to both pH and metals than PS I. Though, nitrate reductase (NR) was more sensitive to both pH and metals, the ATPase was however, more sensitive to metals but less sensitive to acidic pH. Acid pH was found to inhibit the nutrient (NO3- and NH4+) uptake and nitrate reductase in a non-competitive manner. The inhibition produced by the test metals alone was of non-competitive type for NO3- uptake, nitrate reductase and ATPase and competitive for NH4+ uptake. Acidity not only inhibited the metabolic variables directly but also through facilitated uptake of metals and increased membrane permeability. A very low sensitivity of ATPase to acidic pH seems to be responsible for the survival of algae in acid environment.
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PMID:Effect of Cu and Ni on growth, mineral uptake, photosynthesis and enzyme activities of Chlorella vulgaris at different pH values. 802 20

This study concerns the inhibitory effects of acid pH and nickel on growth, nutrient (NO3- and NH4+) uptake, carbon fixation, O2 evolution, electron transport chain and enzyme (nitrate reductase and ATPase) activities of acid tolerant and wild-type strains of Chlorella vulgaris. Though a general reduction in all these variables was noticed with decreasing pH, the tolerant strain was found to be metabolically more active than the wild-type. A reduced cation (NH4+, Na+, K+ and Ca2+) uptake, coupled with a facilitated influx of anions (NH4+, PO4(3-) and HCO3-), suggested the development of a positive membrane potential in acid tolerant Chlorella. Nevertheless, a tremendous increase in ATPase activity at decreasing pH revealed the involvement of superactive ATPase in exporting H+ ions and keeping the internal pH neutral. A difference in Na+ and K+ efflux of the two strains at decreasing pH suggests there is a difference in membrane permeability. The low toxicity of Ni in the acid tolerant strain may be due to the low Ni uptake brought about by a change in membrane potential as well as in permeability. Hence, the development of superactive ATPase and a change in both membrane potential and permeability not only offers protection against acidity, but also co-tolerance to metals.
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PMID:Effect of nickel on certain physiological and biochemical behaviors of an acid tolerant Chlorella vulgaris. 814 21

Nitrate reductase (NR) gene fragments (1.1 kb and 800 bp) from the barley plant were incorporated into pSV2neo and transfected by electroporation into a variety of cell lines of different functionality. Only transfected murine macrophage cell lines demonstrated appreciably enhanced NO2- production (i.e., NR activity) both in the presence and absence of exogenous nitrate (NO3-). Addition of NO3- caused the greatest increase in NO2- production when macrophages were primed with interferon-gamma (INF-gamma) and lipopolysaccharide (LPS). Transfection of RAW 264.7 murine macrophages led to isolation of several novel neomycin-resistant subpopulations designated NR10(1), NR10(2) (both containing the 1.1 kb NR fragment) and NR800(5) (containing the 800 bp NR fragment). Similarly transfected nonleukocytic and leukocytic stem cell lines showed no significant NO2- production. Outside of the macrophage cell lines, only the murine T cell line EL-4 showed evidence of mild nitrite production enhancement. The mechanism of enhanced NO2- formation in NR transfected murine macrophages is unknown. However, study of these novel cells may lead to greater understanding of the expression of a plant NR in mammalian cells and highly controlled production of a cytotoxic molecule (NO2-) in macrophages.
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PMID:Plant nitrate reductase gene fragments enhance nitrite production in activated murine macrophage cell lines. 819 85

Tungsten resistant (Wr) mutants of Het+Nif+Nia+, Het+Nif-Nia+ and Het+Nif+Nia- strains of Nostoc muscorum were isolated with severely defective molybdate transport activity. All such mutants showed vanadium (V)-dependent nitrogenase activity and/or nitrate reductase activity and V-dependent growth on N2-nitrogen and/or NO3(-)-nitrogen and V-dependent NO3(-)-repression of heterocyst formation and nitrogenase activity. None of them grew with molybdenum (Mo) under parallel growth condition. Results strongly suggest the ability of V to replace Mo in N2-assimilation or NO3(-)-assimilation under Mo-deficiency.
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PMID:Mutational replacement of molybdenum by vanadium in assimilation of N2 or NO3- as nitrogen source in the cyanobacterium Nostoc muscorum. 833 16

1. A soluble reduced Methyl Viologen-dependent assimilatory nitrate reductase from Azotobacter vinelandii strain UW136 grown aerobically on nitrate was purified to homogeneity by the criteria of nitrate reductase activity staining, and coincidence of a Coomassie Blue-staining protein band on polyacrylamide gels run under non-denaturing conditions. The specific activity was 3 mumol of NO2- formed/min per mg of protein. 2. Gel filtration on Superose-12 and SDS/PAGE showed that the enzyme had an M(r) of 105,000 and was monomeric. The enzyme contained 1 Mo atom, 4 Fe atoms and 4 acid-labile sulphide atoms per molecule; no evidence for the presence of cytochrome or FAD was found. 3. Mo was present in a molybdenum cofactor, which on extraction was capable of activating apo-(nit-1) nitrate reductase present in crude extracts of nit-1 mutants of Neurospora crassa. 4. As isolated, the enzyme had e.p.r. signals assigned to Mo(V) with g-values g1 = 2.023; g2 = 1.998; g3 = 1.993 and with gav. = 2.004 indicating an unusual environment of Mo in this enzyme. 5. Reduction with S2O4(2-) bleached the e.p.r. signals which, on reoxidation after the addition of NO3(2-) to initiate enzyme turnover, exhibited at short times Mo(V) signals similar to those of dissimilatory nitrate reductases, with g1 = 1.998; g2 = 1.989; g3 = 1.981 and gav. = 1.989. Prolonged incubation subsequently gave a mixture of both e.p.r. species. 6. Neither NADH nor NADPH was effective as an electron donor, but reduced Methyl Viologen (apparent Km 998 microM) and reduced Bromophenol Blue (apparent Km 158 microM) were effective. With these donors the apparent Km values for nitrate were 70 microM and 217 microM respectively.
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PMID:Purification and characterization of the assimilatory nitrate reductase of Azotobacter vinelandii. 838 Sep 91

Subcellular localization and coupling to ATP synthesis were investigated with respect to the denitrifying systems of two fungi, Fusarium oxysporum and Cylindrocarpon tonkinense. Dissimilatory nitrate reductase of F. oxysporum or nitrite reductase of C. tonkinense could be detected in the mitochondrial fraction prepared from denitrifying cells of each fungus. Fluorescence immunolocalization, cofractionation with mitochondrial marker enzymes, and cytochromes provided evidence that the denitrifying enzymes are co-purified with mitochondria. Respiratory substrates such as malate plus pyruvate, succinate, and formate were effective donors of electrons to these activities in the mitochondrial fractions. Moreover, nitrite and nitrate reduction were shown to be coupled to the synthesis of ATP with energy yields (P:NO3- or P:2e ratios) of 0.88 to 1.4, depending upon whether malate/pyruvate or succinate were provided as substrates. Nitrate or nitrite reductase activity was inhibited by inhibitors such as rotenone, antimycin A, and thenoyltrifluoroacetone. Thus, fungal denitrification activities are localized to mitochondria and are coupled to the synthesis of ATP. The existence of these novel respiration systems are discussed with regard to the origin and evolution of mitochondria.
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PMID:Denitrification, a novel type of respiratory metabolism in fungal mitochondrion. 866 75


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