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At least 217 records · Page 12Linked to original sources
PubMed1978

Improved colorimetric method for determining nitrate and nitrate in foods.

A method is described for determining nitrate and nitrite in cured meat products, cheeses, and vegetables. The nitrite is determined colorimetrically by diazotization of sulfanilic acid and subsequent coupling with N-(1-naphthyl)-ethylenediamine. The concentration of nitrate plus nitrite is determined similarly but after reduction of the nitrate to nitrite on a cadmium column. The difference of the 2 values is a measure of the nitrate concentration. The main improvements are replacing the Griess reagent, which contains a carcinogen, with a mixture of sulfanile acid and N-(1-naphthyl)-ethylenediamine, providing for adjustment of pH of the sample suspension during extraction and digestion by heating, and maintaining constant pH by controlled addition of buffers and acids during color development. The method was successfully applied to the analysis of 15 samples of meat products, 23 cheeses, and 6 different vegetables. The average recovery of sodium nitrite added at levels ranging from 10 to 30 ppm was 95% and recovery of sodium nitrate added at levels from 30 to 400 ppm was 94% (corrected for cadmium column efficiency).

Animals↗
PubMed1998

Construction and characterization of nitrate reductase-based amperometric electrode and nitrate assay of fertilizers and drinking water.

The construction and characterization of a nitrate reductase-based amperometric electrode for determination of nitrate ion is described. The electrode consisted of nitrate reductase held by dialysis membrane onto a Nafion-coated glassy carbon electrode. Methyl viologen was allowed to absorb into the Nafion layer, which acted as a reservoir for the electron mediator. The utility of the electrode to assay fertilizer and water sample for nitrate was demonstrated. The assays conducted with this electrode compared well with colorimetric and potentiometric assays of the same samples.

Absorption↗
PubMed2002

Introduction and expression of a deregulated tobacco nitrate reductase gene in potato lead to highly reduced nitrate levels in transgenic tubers.

Twenty transformed Solanum tuberosum plants issued from five different varieties and carrying a chimeric tobacco nitrate reductase gene (a truncated tobacco Nia2 coding sequence fused to the CaMV 35S promoter) were cultivated in field conditions at INRA Ploudaniel in 1999 and 2000. In 60% of the transgenic plants, the presence of the tobacco Nia2 transcript was detected by RT-PCR. These clones exhibited a drastic decrease in the nitrate content in tubers. Indeed the nitrate content decreased by about 95% in the tubers of transformed plants compared to nontransformed potato plants from the same variety. This decrease was correlated with a modified regulation of NR expression as revealed by a higher chlorate sensitivity of these transgenic lines. Two methods of nitrate content determination in tubers were also compared and were found to give similar results.

Base Sequence↗
PubMed2003

Characterization of a nitrate-respiring bacterial community using the nitrate reductase gene (narG) as a functional marker.

Bacterial cultures capable of reducing nitrate to nitrite, or of complete denitrification, were established from 5, 10, 15 and 20 cm depths of a freshwater sediment. Taxonomic analysis of the 56 isolates using 16S rRNA gene sequences revealed an unexpected species richness, which included representatives of the gamma-Proteobacteria, Bacillus spp., Staphylococcus spp. and members of the Actinobacteria. Gram-positive species tended to predominate in the lower depths of the sediment, where there was evidence of active sulphate respiration. Sequences (from the narG gene) potentially encoding the catalytic subunit of the membrane-associated nitrate reductase were successfully amplified from 46 of the isolates, using a nested PCR with four degenerate primers. NarG sequences clustered into three major groupings that were supported by alternative phylogenetic analyses. The NarG sequences from Gram-positive isolates (according to rRNA gene phylogeny) clustered together within sequences from the low-G+C Gram-positive bacteria. However, this cluster also included two sequences from members of the genus Pseudomonas. Another group contained mostly NarG sequences from the Proteobacteria (according to rRNA gene phylogeny), but also included five sequences from Gram-positive species. The third group of NarG sequences contained three sequences from Gram-positive species. Thus, the NarG-derived phylogeny is not entirely consistent with 16S rRNA-based taxonomy, precluding the use of the narG gene as a taxonomically useful tool for the characterization of nitrate-respiring bacteria. Total DNA was also extracted from the four depth intervals of the sediment sample and used in similar narG amplifications. Most sequences amplified directly from environmental DNA clustered in the Gram-negative group, and none was in the predominantly Gram-positive group. The study also revealed a degree of spatial organization of a nitrate-respiring community in terms of both microbiology and narG sequences.

Bacteria↗
PubMed1996

Developmental stage-specific and nitrate-independent regulation of nitrate reductase gene expression in rapeseed.

cDNA clones for two isogenes of nitrate reductase (NR) have been isolated from rapeseed (Brassica napus L.) androgenetic haploid embryos induced by microspore culture. NR mRNA accumulation can be detected by northern hybridization at 14 d after culture initiation when embryos develop to the heart/torpedo-shaped stage. Whole-mount in situ hybridization experiments demonstrate that the mRNA accumulation is developmental stage specific. In addition, even when cultured in media containing no nitrate, embryos accumulated NR mRNA to almost the same level as the control. This indicates the unique regulation of NR in embryogenesis in which NR mRNA transcription is activated in a developmental stage-specific manner that is independent of nitrate induction. In zygotic embryogenesis, a stage-specific accumulation of NR mRNA was also observed. By contrast, the obvious effect of nitrate on NR expression that has been reported in many plant species was also confirmed in rapeseed leaf. Quantitative combined reverse transcription-polymerase chain reaction analysis suggests that the flexible and variable regulation of NR expression, which is organ specific, nitrogen metabolite specific, and developmental stage specific, is caused principally by regulation of one major structural gene.

Base Sequence↗
PubMed2005

Highly efficient nitration of phenolic compounds in solid phase or solution using Bi(NO3)3.5H2O as nitrating reagent.

[reaction: see text] Bi(NO(3))(3).5H(2)O was used as an efficient nitrating reagent in the nitration of phenolic compounds to give nitrated phenols in good to high yields. The nitration reaction proceeded smoothly by grinding 1 equiv of phenol, 2-methylphenol, 4-methylphenol, or 4-chlorophenol and Bi(NO(3))(3).5H(2)O, and the nitration of other phenolic compounds could be performed in acetone at ambient temperature (22-30 degrees C).

Journal Article↗
PubMed1978

Preferential nitration with tetranitromethane of a specific tyrosine residue in penicillinase from Staphylococcus aureus PCl. Evidence that the preferentially nitrated residue is not part of the active site but that loss of activity is due to intermolecular cross-linking.

1. Nitration of tyrosine residues of staphylococal penicillinase was accompanied by a partial loss of enzymic activity, which was not readily explained by nitration of a single residue. 2. Loss of activity correlated with low recovery of tyrosine plus nitrotyrosine, which was consistent with cross-linking. 3. The fraction of treated enzyme that was eluted from Sephadex G-75 earlier than native penicillinase was similar to the fraction of enzyme activity lost. Protein eluted in positions corresponding to monomer, dimer and higher oligomers respectively showed major bands in corresponding positions in sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, indicating that the increase in molecular weight was due to intermolecular cross-linking. Monomeric enzyme containing up to 4 mol of nitrotyrosine/mol retained full catalytic activity. Dimeric enzyme retained 50% of normal activity, whereas higher oligomers retained an average of 8-15% of normal activity. 4. Monomeric enzyme isolated after treatment with equimolar tetranitromethane was nitrated predominantly at tyrosine-72.5. Reaction of reduced nitrated monomer with 1,5-difluoro-2,4-dinitrobenzene gave a monomeric, apparently cross-linked product with full catalytic activity. 6. It is concluded that tyrosine-72 plays no part in the active site. Its preferential nitration may be due to its being insufficiently exposed to be available for intermolecular cross-linking. This poperty may make it useful for attachment of a reporter group.

Amino Acids↗
PubMed2000

Single-dose miconazole nitrate vaginal ovule in the treatment of vulvovaginal candidiasis: two single-blind, controlled studies versus miconazole nitrate 100 mg cream for 7 days.

To determine the efficacy and safety of a single-dose (1200 mg) soft gel insert (vaginal ovule) with miconazole nitrate (2%) topical cream compared with Monistat 7 (miconazole nitrate 2%) Vaginal Cream (Advanced Care Products, North Brunswick NJ) in treating vulvovaginal candidiasis (VVC), two randomized, single-blind, multicenter, controlled, comparative phase III studies were performed. Five hundred fifty-eight patients received either a single-dose miconazole nitrate (1200 mg) ovule or seven consecutive doses of Monistat 7. Ovule arm patients also received miconazole nitrate 2% cream for symptom relief, as needed, up to twice daily. The primary end point was a therapeutic cure. Also evaluated were time to complete symptom relief, safety, and patient preference. The ovule had overall cure rates of 71.7% (71 of 99 patients) and 61.5% (64 of 104 patients). Monistat 7 had overall cure rates of 70.1% (68 of 97 patients) and 61.1% (55 of 90 patients). A significantly greater proportion of patients experienced complete symptom relief by day 3 with the ovule (p = 0.008 and p = 0.025), and time to complete relief was significantly faster (median 4 versus 5 days and 3 versus 4 days). Overall safety results were consistent between groups in both studies. Miconazole nitrate vaginal ovule is as safe and efficacious in curing VVC as Monistat 7 while providing complete symptom relief significantly faster. Patients preferred the ovule to prior therapy.

Administration, Intravaginal↗
PubMed1976

Effect of light and glucose on the induction of nitrate reductase and on the distribution of nitrate in etiolated barley leaves.

Barley seedlings grown in the dark with 10 mm KNO(3) have low levels of nitrate reductase activity even though large amounts of No(3) (-) accumulate in the leaves. When the leaves are excised and transferred to the light, there is an increase in nitrate reductase activity both in the presence and absence of exogenous NO(3) (-). When the leaves are transferred to a glucose solution (0.05 m) but kept in the dark, induction of nitrate reductase activity occurs only when fresh NO(3) (-) is added to the system.In dark-grown leaves, there are small traces of NO(3) (-) in a "metabolic pool." Addition of glucose does not alter this distribution. Light, on the other hand, results in an appreciable accumulation of NO(3) (-) in the metabolic pool. There is a linear correlation between nitrate reductase activity and the size of the metabolic NO(3) (-) pool. Our results thus suggest that NO(3) (-) accumulates in a storage pool when seedlings are grown in continuous darkness. The transfer of this NO(3) (-) to an active metabolic pool is mediated by light but not by glucose. We believe that this transfer of NO(3) (-) leads to the induction of nitrate reductase. When NO(3) (-) is included in the medium, both light and glucose increase its incorporation into the metabolic pool. The results suggest two mechanisms for regulating the metabolic NO(3) (-) pool: (a) a transfer from the storage pool which requires light; and (b) a transfer from the external medium which requires either glucose or light.

Journal Article↗
PubMed1979

Effects of red, far red, and blue light on enhancement of nitrate reductase activity and on nitrate uptake in etiolated rice seedlings.

The effects of red (R), far red (FR), or blue light (B) on the enhancement of nitrate reductase (NR) activity and on nitrate uptake in etiolated rice seedlings were examined. On 5-minute illumination followed by 12-hour dark, R caused marked increase of NR activity, but FR and B caused only slight increase. Illumination with 560 ergs per square centimeter per second of R for 5 minutes caused maximal increase. The effect of R was almost completely counteracted by subsequent illumination with 2,000 ergs per square centimeter per second of FR for 10 minutes, indicating that NR induction was mediated by phytochrome. Exogenous supply of inducer nitrate was not required during the 5-minute illumination and the R-FR cycles, if the seedlings were transferred to nitrate solution at the beginning of the dark incubation. NR activity in the shoots was found high when shoots were illuminated but was low when only roots were illuminated. On continuous illumination for 12 hours, B had more effect on NR increase than R.Nitrate uptake during 6-hour dark was not increased by exposure to R, FR, or B for 5 minutes at the beginning. On continuous illumination for 6 hours, R slightly increased nitrate uptake, whereas FR and B had no effect.

Journal Article↗
PubMed1979

In Vitro Stability of Nitrate Reductase from Wheat Leaves: III. Isolation and Partial Characterization of a Nitrate Reductase-inactivating Factor.

A nitrate reductase (EC 1.6.6.1)-inactivating factor has been isolated from 8-day-old wheat leaves. The purification schedule involved ammonium sulfate precipitation, Sephadex G-100 filtration, DEAE-cellulose chromatography, and Sephadex G-150 filtration. No accurate assessment could be made as to the degree of purification relative to crude extract as the inactivating factor could not be detected in crude extract. However a 2,446-fold purification was achieved from the ammonium sulfate fraction to the pooled enzyme from the Sephadex G-150 step.The inactivating factor was heat-labile and had a molecular weight of 37,500. The inactivating factor was particularly sensitive to the divalent metal chelators, 1,10-phenanthroline and bathophenanthroline. Evidence indicated that Fe(2+) may be the functional metal. The trypsin inhibitors N-alpha-p-tosyl-l-lysine chloromethyl ketone and alpha-N-benzoyl-l-arginine were inhibitory. However, phenylmethyl sulfonyl fluoride, an inhibitor of serine peptide hydrolases, was not inhibitory. Neither casein nor hemoglobin nor a range of artificial substrates were hydrolyzed by the inactivating factor. Highly purified wheat leaf nitrite reductase (EC 1.7.99.3) and ribulose 1,5-bisphosphate carboxylase:oxygenase (EC 4.1.1.39) were not affected by the nitrate reductase-inactivating factor.The inactivating factor was more active toward the NADH-nitrate reductase compared to either of the component enzymic activities flavin adenine mononucleotide-nitrate reductase and methyl viologen-nitrate reductase. The NADH-ferricyanide reductase (diaphorase) component was the least sensitive.

Journal Article↗
PubMed1989

Nitrate effects on nitrate reductase activity and nitrite reductase mRNA levels in maize suspension cultures.

Nitrate reductase (NR) activity and nitrite reductase (NiR) mRNA levels were monitored in Black Mexican Sweet maize (Zea mays L.) suspension cultures after the addition of nitrate. Maximal induction occurred with 20 millimolar nitrate and within 2 hours. Both NR and NiR mRNA were transiently induced with levels decreasing after the 2 hours despite the continued presence of nitrate in the medium. Neither ammonia nor chlorate prevented the induction of NR. Furthermore, removal of nitrate, followed by its readdition 22 to 48 hours later, did not result in reinduction of activity or message. NR was synthesized de novo, since cycloheximide completely blocked its induction. Cycloheximide had no effect on the induction of NiR mRNA or on the transient nature of its induction. These results are similar to those reported previously for maize seedlings.

Journal Article↗
PubMed2000

Transcription of a nitrate reductase gene isolated from the symbiotic basidiomycete fungus Hebeloma cylindrosporum does not require induction by nitrate.

Ectomycorrhizal fungi contribute to the nitrogen nutrition of their host plants, but no information is available on the molecular control of their nitrogen metabolism. The cloning and pattern of transcriptional regulation of two nitrite reductase genes of the symbiotic basidiomycete Hebeloma cylindrosporum are presented. The genomic copy of one of these genes (nar1) was entirely sequenced; the coding region is interrupted by 12 introns. The nar1 gene, which is transcribed and codes for a putative 908-amino acid polypeptide complemented nitrate reductase-deficient mutants of H. cylindrosporum upon transformation, thus demonstrating that the gene is functional. The second gene (nar2), for which no mRNA transcripts were detected, is considered to be an ancestral, non-functional duplication of nar1. In a 462-nt partial sequence of nar2 two introns were identified at positions identical to those of introns 8 and 9 of nar1, although their respective nucleotide sequences were highly divergent; the exon sequences were much more conserved. In wild-type strains, transcription of nar1 is repressed in the presence of a high concentration of ammonium. High levels of transcription are observed in the presence of either very low nitrogen concentrations or high concentrations of nitrate or organic N sources such as urea, glycine or serine. This indicates that in H. cylindrosporum, in contrast to all nitrophilous organisms studied so far, an exogenous supply of nitrate is not required to induce transcription of a nitrate reductase gene. In contrast, repression by ammonium suggests the existence of a wide-domain regulatory gene, as already characterized in ascomycete species.

Agaricales↗
PubMed1989

Evidence for a plasma-membrane-bound nitrate reductase involved in nitrate uptake of Chlorella sorokiniana.

Anti-nitrate-reductase (NR) immunoglobulin-G (IgG) fragments inhibited nitrate uptake into Chlorella cells but had no affect on nitrate uptake. Intact anti-NR serum and preimmune IgG fragments had no affect on nitrate uptake. Membrane-associated NR was detected in plasma-membrane (PM) fractions isolated by aqueous two-phase partitioning. The PM-associated NR was not removed by sonicating PM vesicles in 500 mM NaCl and 1 mM ethylenediaminetetraacetic acid and represented up to 0.8% of the total Chlorella NR activity. The PM NR was solubilized by Triton X-100 and inactivated by Chlorella NR antiserum. Plasma-membrane NR was present in ammonium-grown Chlorella cells that completely lacked soluble NR activity. The subunit sizes of the PM and soluble NRs were 60 and 95 kDa, respectively, as determined by sodium-dodecyl-sulfate electrophoresis and western blotting.

Biological Transport↗
PubMed1979

[Effect of nitrate and cytokinin on nitrate reductase activity in isolated corncockle embryos].

The effects of cytokinin and nitrate on the activity of nitrate reductase (NR) in isolated embryos of Agrostemma githago L. were studied. It was shown that the effects of cytokinin and NO-3 on the induction of NR is additive during 8, 12 and 18 hrs of embryos incubation in the solutions of the two inducers. Anticytokinin decreased the cytokinin induced NR by 35--39% and had no effect on the NR induction by nitrate. The substrate and hormonal induction of NR differed in the duration of the lag period. This difference dependent on the physiological state of the embryos at the beginning of incubation. The data obtained are indicative of the independence of cytokinin and NO-3 effects on the NR synthesis in isolated embryos of Agrostemma githago L. Abscisic acid supressed cytokinin- and nitrate-induced NR and had practically no effect on total incorporation of the label into the protein. It is assumed that the induced synthesis of the protein is more sensitive to the action of abscisic acid that the total protein synthesis.

Abscisic Acid↗
PubMed1977

Nitrate fertilizers as environmental pollutants: positive correlation between nitrates (NaNO3 and KNO3) used per unit area and stomach cancer mortality rates.

Since a significant positive correlation between nitrate fertilizer exposure and stomach cancer mortality has been found, a study of nitrate fertilizer pollution in arable land in terms of amount of nitrates used per unit area (kg/ha) and stomach cancer death rates was carried out. The regression of death rates for stomach cancer, standardized for age, on the nitrates used per unit area, by province (N = 25), exhibited a significant association between the 2 variables (p less than 0.004). When industrialized provinceds (N = 3) were not considered, a highly significant association was found (F = 16.47; d.f. = 1, 20; p less than 0.0006). The correlation coefficient was + 0.672.

Carcinogens↗
PubMed2004

Disruption of the nitrate transporter genes AtNRT2.1 and AtNRT2.2 restricts growth at low external nitrate concentration.

The high-affinity transport systems in Arabidopsis thaliana (L.) Heynh. involve potentially seven genes. Among these, the AtNRT2.1 and/or AtNRT2.2 genes have been shown to play a major role in the inducible component of this transport system. The physiological impact of a disruption of AtNRT2.1 and AtNRT2.2 on plant growth and N-metabolism was investigated. The reduced nitrate uptake in the mutant under a limiting N-regime was found to correlate with a significant difference in shoot/root ratio between wild type and mutant and a drastically reduced nitrate level in the shoot of the mutant. Carbohydrate analyses of plants under a low nitrate supply revealed a slight increase in glucose and fructose in the mutant shoots as well as an increase in sucrose and starch contents in mutant shoots. Interestingly, the AtNRT2.4 and AtNRT2.5 genes were over-expressed in the mutant growing in reduced N-conditions, without any compensation by root nitrate influx. These results are discussed in the context of the putative role of the different NRT2 genes.

Anion Transport Proteins↗
PubMed1989

The narK gene product participates in nitrate transport induced in Escherichia coli nitrate-respiring cells.

The nucleotide sequence of the Escherichia coli narK gene, which is located in the upstream region of the narCHJI operon, was determined. The narK gene encodes a very hydrophobic protein with 463 amino acid residues (Mr 49,693). A narK deletion mutant, under conditions for the induction of nitrate respiration, was unable to perform nitrate transport. Loss of transport activity was recovered by transforming the mutant with a narK+ plasmid. Thus, we conclude that the narK gene encodes a transmembrane protein participating in nitrate transport. In the narK promoter region, we defined a unique sequence that we designate as a 'nitrate box', functioning as a putative NarL-binding site, in addition to the consensus sequence of the 'anaero-box'.

Amino Acid Sequence↗