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PubMed2004

Side-on copper-nitrosyl coordination by nitrite reductase.

A copper-nitrosyl intermediate forms during the catalytic cycle of nitrite reductase, the enzyme that mediates the committed step in bacterial denitrification. The crystal structure of a type 2 copper-nitrosyl complex of nitrite reductase reveals an unprecedented side-on binding mode in which the nitrogen and oxygen atoms are nearly equidistant from the copper cofactor. Comparison of this structure with a refined nitrite-bound crystal structure explains how coordination can change between copper-oxygen and copper-nitrogen during catalysis. The side-on copper-nitrosyl in nitrite reductase expands the possibilities for nitric oxide interactions in copper proteins such as superoxide dismutase and prions.

Alcaligenes faecalis↗
PubMed1996

Positive regulation by nitrite of the nitrate assimilation operon in the cyanobacteria Synechococcus sp. strain PCC 7942 and Plectonema boryanum.

In the absence of fixation of ammonium to glutamine, nitrate and nitrite activated transcription of the nitrate assimilation (nirA-nrtABCD-narB) operon of Synechococcus sp. strain PCC 7942. In a nitrate reductase-deficient mutant, only nitrite activated transcription, indicating that nitrite is the actual activator of the operon. Nitrate and nitrite were also found to activate the transcription of a nitrate assimilation operon in the filamentous nonheterocystous nitrogen-fixing cyanobacterium Plectonema boryanum.

Anion Transport Proteins↗
PubMed1998

cis-acting sequences required for NtcB-dependent, nitrite-responsive positive regulation of the nitrate assimilation operon in the cyanobacterium Synechococcus sp. strain PCC 7942.

There are three binding sites for NtcA (nirI, nirII, and nirIII), the global nitrogen regulator of cyanobacteria, in the DNA region between the two divergently transcribed operons (nirA and nirB operons) involved in nitrate assimilation in Synechococcus sp. strain PCC 7942. Using the luxAB reporter system, we showed that nirI and nirIII, which are located 23 bp upstream from the -10 promoter element of nirA and nirB, respectively, are required for induction by nitrogen depletion of the nirA and nirB operons, respectively. The induction of nirA operon transcription was a prerequisite for the nitrite-responsive positive regulation of the transcription by NtcB, a LysR-type protein. The NtcA-binding site nirII, located in the middle of the nirA-nirB intergenic region, and a potential binding site for a LysR-type protein (TGCAN5TGCA; designated L1), located between nirI and nirII, were required for the nitrite-responsive, NtcB-dependent enhancement of nirA operon transcription. Although the requirement for the L1 site was consistent with the involvement of the LysR family protein NtcB in transcriptional regulation, NtcB did not bind to the nirA regulatory region in vitro in the presence of nitrite and NtcA, suggesting the involvement of some additional factor(s) in the regulation. An L1-like inverted repeat with the consensus sequence TGCN7GCA was conserved in the nirA promoter region of cyanobacteria, being centered at position -23 with respect to the NtcA-binding site corresponding to nirI, which suggested the common occurrence of nitrite-responsive regulation of the nitrate assimilation operon among cyanobacteria.

Bacterial Proteins↗
PubMed2005

The Pasteurella multocida nrfE gene is upregulated during infection and is essential for nitrite reduction but not for virulence.

Pasteurella multocida is the causative agent of a range of diseases with economic importance in production animals. Many systems have been employed to identify virulence factors of P. multocida, including in vivo expression technology (IVET), signature-tagged mutagenesis, and whole-genome expression profiling. In a previous study in which IVET was used with P. multocida, nrfE was identified as a gene that is preferentially expressed in vivo. In Escherichia coli, nrfE is part of the formate-dependent nitrite reductase system involved in utilizing available nitrite as an electron accepter during growth under anaerobic conditions. In this study, we constructed an isogenic P. multocida strain that was unable to reduce nitrite under either aerobic or anaerobic conditions, thereby demonstrating that P. multocida nrfE is essential for nitrite reduction. However, the nrfE mutant was still virulent in mice. Real-time reverse transcription-PCR analysis indicated that nrfE was regulated independently of nrfABCD by an independent promoter that is likely to be upregulated in vivo.

Animals↗
PubMed1989

Chronic toxicity tests of sodium thiocyanate with sodium nitrite in F344 rats.

Sodium thiocyanate, a common environmental chemical, was found to increase the incidence of liver tumors in a group of rats treated with 0.08% in drinking water. To test the possibility that thiocyanate was catalyzing the formation of carcinogenic nitrosamines from amines and nitrite in the food, a group of 20 male and 20 female rats was given a higher dose of sodium thiocyanate (0.32%) together with sodium nitrite (0.2%) in drinking water. Similar groups of rats were given 0.32% sodium thiocyanate or 0.2% sodium nitrite in drinking water or were untreated. All treatments lasted most of the lifetime of the rats, at least 2 years. There was no difference between the groups, treated or untreated, in survival, or in the incidence of any tumor that could be related to the treatment. The results indicate that sodium thiocyanate is without carcinogenic activity in rats, alone or combined with sodium nitrite.

Animals↗
PubMed2005

The existence and significance of a mitochondrial nitrite reductase.

The physiological functions of nitric oxide (NO) are well established. The finding that the endothelium-derived relaxing factor (EDRF) is NO was totally unexpected. It was shown that NO is a reaction product of an enzymatically catalyzed, overall, 5-electron oxidation of guanidinium nitrogen from L-arginine followed by the release of the free radical species NO. NO is synthesized by a single protein complex supported by cofactors, coenzymes (such as tetrahydrobiopterin) and cytochrome P450. The latter can uncouple from substrate oxidation producing O2*- radicals. The research groups of Richter [Ghafourifar P, Richter C. Nitric oxide synthase activity in mitochondria. FEBS Lett 1997; 418: 291-296.] and Boveris [Giulivi C, Poderoso JJ, Boveris A. Production of nitric oxide by mitochondria. J Biol Chem 1998; 273: 11038-11043.] identified a mitochondrial NO synthase (NOS). There are, however, increasing reports demonstrating that mitochondrial NO is derived from cytosolic NOS belonging to the Ca2+-dependent enzymes. NO was thought to control cytochrome oxidase. This assumption is controversial due to the life-time of NO in biological systems (millisecond range). We found a nitrite reductase in mitochondria which is of major interest. Any increase of nitrite in the tissue which is the first oxidation product of NO, for instance following NO donors, will stimulate NO-recycling via mitochondrial nitrite reductase. In this paper, we describe the identity and the function of mitochondrial nitrite reductase and the consequences of NO-recycling in the metabolic compartment of mitochondria.

Animals↗
PubMed1989

[Assessment of the degree of carcinogenicity of small doses of nitrites].

Chronic experiments on CBA and C57B1 mice and acute experiments on CBA mice established: (a) carcinogenic effect of sodium nitrite given continuously with drinking water (0.1; 1.0 and 10.0 maximum allowable concentration) in combination with morpholine fed with bread, and (b) endogenous synthesis of nitrosomorpholine as a result of simultaneous intragastric administration of same doses of sodium nitrite and morpholine. Also, nitrosomorpholine and N-nitrosodimethylamine synthesis was observed in vitro following addition of low-dose sodium nitrite, morpholine and amidopyrine to human gastric juice. Carcinogenic hazard associated with low-dose nitrite consumption in humans is discussed.

Aminopyrine↗
PubMed1985

[Transplacental effect of sodium nitrite on rat lung cells with their subsequent culture in the medium with precursors of N-nitrosodimethylamine].

Mongrel rats of 12th day of pregnancy were administered sodium nitrite, amidopyrine, mixture of these substances and N-nitrosodimethylamine (NDMA) as well as alpha-tocopherol + ascorbic acid with drinking water. The cultivated lung cells of 3-day newborn rats with NDMA and its precursors were incubated. The transplacental effect of sodium nitrite on rat lung cells was observed. It was manifested in a decrease of the cell suspension viability, in an increase of the pathological mitosis level as well as in changes in cell responses to NDMA. The combination of sodium nitrite with phenobarbital considerably increased sensitivity of cells to the effect of NDMA, mixture of sodium nitrite with amidopyrine and amidopyrine.

Aminopyrine↗
PubMed1984

An in vitro effect of ascorbate on the spontaneous reduction of sodium nitrite concentration in a reaction mixture.

Nitrite is known to react with free amines to form nitrosamines which may have carcinogenic activity. The present study provides evidence showing that addition of ascorbic acid in a reaction mixture results in a spontaneous decrease in nitrite concentration. The nitrite lowering effect of ascorbic acid appears to correlate with the rate of oxidation of the vitamin to dehydroascorbic acid, suggesting that ascorbic acid may be involved in the reduction of nitrite to nitrogen oxide.

Ascorbic Acid↗
PubMed1984

Nitrosation by alkyl nitrites. Catalysis by inorganic salts.

Isobutyl nitrite is an effective nitrosating agent at acidic, neutral and basic pH in the presence of species arising from phosphate ion. The reaction is first-order in isobutyl nitrite and amine. In the reaction of isobutyl nitrite with sulfanilamide, the pH dependence reflects the change in concentration of the various protonated forms of phosphate, with H3PO4 and H2PO4- most strongly affecting the rate. In the reaction of isobutyl nitrite with dipropylamine, the pH dependence also reflects the change in the concentration of unprotonated amine.

Catalysis↗
PubMed1984

Ester-mediated nitrosamine formation from nitrite and secondary or tertiary amines.

N-Nitrosamines are formed from the heating of either a secondary or a tertiary amine with sodium nitrite in the presence of a high-boiling ester such as 2-acetoxyethanol in ethylene glycol. The four secondary and six tertiary amines examined were found to produce N-nitrosamines in yields ranging from 4% to 80% when equimolar amounts of amine and ester were heated at 120 degrees C with one- to ten-fold equivalents of sodium nitrite in ethylene glycol. Secondary amines competitively produced acetamides at a rate slightly greater than N-nitrosamine formation. Preincubation of a large excess of sodium nitrite and ester led to the rapid formation of N-nitrosamines in high yield. The reaction of tribenzylamine resulted in the formation of both benzaldehyde and dibenzylnitrosamine. N,N-Dimethylbenzylamine reacted to give nearly equimolar amounts of N-nitrosodimethylamine and N-nitroso-N-methylbenzylamine. It is proposed that the nitrosating agent is a nitrous ester, and it is shown that 2-benzoxyethyl nitrite rapidly nitrosates secondary and tertiary amines under these reaction conditions. It is also proposed that these transformations are good models for the environmental formation of N-nitrosamines in foods and commercial products.

Amines↗
PubMed1978

Enhanced hepatotoxicity of carbon tetrachloride following sodium nitrite pretreatment.

The administration of sodium nitrite (60 mg/kg, s.c.) 30 min prior to carbon tetrachloride intoxication (2 ml/kg, p.o.) significantly enhanced the rise in serum glutamic oxaloacetic transaminase, glutamic pyruvic transaminase, and isocitrate dehydrogenase. Sodium nitrite pretreatment also enhanced the carbon tetrachloride-induced decrease in hepatic microsomal glucose-6-phosphatase activity. Microsomal diene conjugation absorption indicative of microsomal lipid peroxidation was observed following carbon tetrachloride intoxication, but was not altered by sodium nitrite pretreatment. The data indicate a potentially toxic interaction between sodium nitrite-induced methemoglobinemia and carbon tetrachloride-induced hepatic injury.

Animals↗
PubMed1981

Experimental verification of the possibility of in vivo formation of nitrosocompounds upon combined action of dodecylguanidineacetate and sodium nitrite.

The pollution of the environment with pesticides of different chemical classes (amines, carbamates, guanidines, etc.) and nitrogen fertilizers creates the danger of the in vivo formation of carcinogenic nitrosocompounds. The fungicide Dodin represents dodecylguanidineacetate (DGA), whose chemical structure presupposes a possibility for nitrosofication in the presence of nitrites. The experiments were carried out on albino rats in which 1/10 LD50 sodium nitrite and DGA were introduced orally and in combination. On the 1st, 2nd, 4th, 8th, 15th and 30th days after the onset of the effect we determined the activity of the oxidases with mixed function (OMF) at two levels of biological organization: at the level of intact organism after loading with aminopyrine (AP) and subsequent determination of its basic metabolites in the urine; at subcellular level (microsomal liver fraction) - by the velocity of N-demethylation of AP, hydroxylation of aniline and by the cytochrome P-450 content. The independent action of sodium nitrite leads to a slight inhibition of OMF at subcellular level (28--34%) only after a single treatment. DGA does not change the activity of OMF. The combined action of the two agents causes considerable OMF inhibition (63--67 per cent) on the 1st, 2nd, 4th and 15th days at both levels. The concentration of microsomal protein decreases parallel to OMF inhibition. The data obtained suggest that a new compound is formed under the conditions of the experiment, probably through in vivo nitrosification of the pesticide. This is also testified by the established qualitatively different effect of the preliminary induction of OMF with phenobarbital on the acute toxicity of the noxae studied: lack of effect for DGA, increase for sodium nitrite and decrease for their combination.

Animals↗
PubMed1994

Rush hemolysis. A 'bite-cell' hemolytic anemia associated with volatile liquid nitrite use.

Volatile nitrites are illegally marketed compounds that have been inhaled by persons who believe that they cause sexual arousal. These substances have been associated with significant hemolysis of red blood cells in patients with decreased or normal glucose-6-phosphate dehydrogenase levels because such nitrites act as cell-membrane oxidants. We report herein a case of hemolysis in a patient with an underlying glucose-6-phosphate dehydrogenase deficiency associated with the use of volatile nitrites, and we also review the literature of volatile nitrite-induced hemolytic anemia.

Adolescent↗
PubMed1999

Nitrate and nitrite in vegetables from areas affected by war-time operations in Croatia.

To evaluate nitrate and nitrite contents in cabbage and potatoes, the most consumed vegetables in Croatia, and to examine if war-time operations in Croatia affected nitrate and nitrite levels in vegetables, potatoes and cabbage cultivated in the war region (East Slavonia) and out of war regions were analyzed. Data showed that nitrate contents were higher in the samples from the war region (32% and 24% in potatoes and cabbage, respectively) but differences were not statistically significant. The nitrate levels found in potato samples (196 mg NaNO3/kg fresh weight (FW) and cabbage samples (911 mg NaNO3/kg FW) were comparable with levels reported for other countries. The nitrite contents in potatoes (321 micrograms NaNO2/kg FW) and cabbage (173 micrograms NaNO2/kg FW) were lower than the contents reported for most other countries. Further examinations of nitrate and nitrite concentrations in vegetables in Croatia as well as examinations of the influence of war-time operations on accumulation of these toxic contaminants are necessary.

Brassica↗
PubMed2000

Cloning, sequencing, and expression of H.a.YNR1 and H.a.YNI1, encoding nitrate and nitrite reductases in the yeast Hansenula anomala.

A single Hansenula anomala genomic DNA fragment containing the genes H.a.YNR1 (yeast nitrate reductase) and H.a.YNI1 (yeast nitrite reductase) encoding nitrate and nitrite reductase, respectively, was isolated from a lambda EMBL3 genomic DNA library. As probe, a 3.2 kb DNA fragment isolated from a lambda gt11 H. anomala genomic DNA library screened with antiserum anti-NR from H. anomala was used. H. a.YNR1 and H.a.YNI1 genes are separated by 473 bp and encode putative proteins of 870 and 1077 amino acids, respectively, with great similarity to nitrate and nitrite reductases from other organisms. Northern blot analysis revealed that both genes are highly expressed in nitrate, very low in nitrate plus ammonium, and no expression was detected in ammonium or nitrogen-free media. Levels of nitrate reductase and nitrite reductase were very low or undetectable by Western blot analysis in nitrogen-free and ammonium media, whereas both proteins were present in nitrate and ammonium plus nitrate media. The nucleotide sequence Accession No. is AF123281.

Amino Acid Sequence↗
PubMed1995

The determination of nitrite and nitrate in human blood plasma by capillary zone electrophoresis.

The determination of nitrite and nitrate in human blood plasma by capillary zone electrophoresis (CZE) is described. Electrophoresis was carried out in a 65 cm long, 75 microns wide silica capillary, using 750 mM sodium chloride containing 5% NICE-Pak OFM Anion-BT (an additive reversing the electroosmotic flow) as running buffer, at a potential of 20 kV, with on-column UV detection at 214 nm. Under these conditions, the two anions migrated in the order of nitrite and nitrate, completely resolved from each other. Forty-one samples of ultrafiltered blood plasma of healthy volunteers were analyzed. The concentrations of nitrite and nitrate were 0.15 +/- 0.07 mg/L and 3.2 +/- 1.6 mg/L (mean +/- SD), respectively, with a linear correlation in the range of 0.1-50 mg/L. The within-day and between-day coefficients of variation (CVs) for nitrite and nitrate were lower than 5% and 8%, respectively. The recovery was 97-114%. The estimated plasma volume needed for each determination was 108 nL.

Electrophoresis, Capillary↗
PubMed2006

Simultaneous analysis of nitrate and nitrite in a microfluidic device with a Cu-complex-modified electrode.

A CE microsystem coupled with a microchip and a copper-(3-mercaptopropyl) trimethoxysilane (Cu-MPS) complex-modified carbon paste electrode (CPE) was developed for the simultaneous analysis of nitrite and nitrate. The method is based on the electrocatalytic reduction of both analytes with the modified electrode. The Cu-MPS complex was characterized by voltammetric, XPS, and FT-IR analyses. Experimental parameters affecting the sensitivity of the modified electrode were assessed and optimized. The best separation was achieved in a 60 mm separation channel filled with a 20 mM acetate buffer of pH 5.0 containing 3.0 mM CTAB at separation field strength of -250 V/cm within 90 s. The detection potential for the simultaneous analysis of nitrite and nitrate was found to be -225 mV versus Ag/AgCl. A reproducible response (RSD of 3.2% (nitrite) and 2.8% (nitrate), n = 8) for repetitive sample injections reflected the negligible electrode fouling at the modified CPE. The interference effect was examined for other inorganic ions and biological compounds. A wide hydrodynamic range between 0.25 and 120 microM was observed for analyzing nitrite and nitrate with the sensitivities of 0.069 +/- 0.003 and 0.065 +/- 0.002 nA/microM, and the detection limits, based on S/N = 3, were found to be 0.09 +/- 0.007 and 0.08 +/- 0.009 microM, respectively. The applicability of the method to water and urine samples analyses was demonstrated.

Copper↗