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PubMed1987

Prosthetic group content and ligand-binding properties of spinach nitrite reductase.

Chemical analysis of the ferredoxin-dependent native form (Mr = 85,000) of spinach nitrite reductase has demonstrated a siroheme content that approaches 2 mol of siroheme/mol of enzyme. A widely studied modified (Mr = 61,000) form of nitrite reductase, that has lost much of the native enzyme's ability to use ferredoxin as an electron donor, contains approximately 1 mol of siroheme/mol of enzyme. Quantitation of the high spin ferri-siroheme EPR signals and of nitrite-binding sites of the two preparations confirmed that the native enzyme's siroheme content is approximately twice that of the modified enzyme. Plots of nitrite and cyanide binding to the native enzyme versus ligand concentration are sigmoidal, with Hill coefficients of 1.6-1.8 and 2.3-2.8, respectively. Plots of enzyme activity versus nitrite concentration for the native enzyme are sigmoidal with a Hill coefficient of 2.4. Cyanide inhibition of enzymatic activity was shown to be not competitive. Addition of cyanide to the native enzyme resulted in a diminution of the high spin ferri-siroheme EPR signal and produced EPR signals with g values of 2.71, 2.33, and 1.49 due to low spin ferri-siroheme.

Binding Sites↗

PubMed1985

Effects of sodium nitrite and potassium sorbate on in vitro cultured mammalian cells.

The food additives sodium nitrite and potassium sorbate had cytostatic and cytotoxic effects on in vitro cultured V79 hamster cells and EUE human fibroblasts if administered in an acid environment (pH 4.95). The strong cytotoxic effect of sodium nitrite and that of the combined action of sodium nitrite and potassium sorbate was observed along the inhibition of macromolecular synthesis. In this respect, potassium sorbate was less effective. The decreased plating efficiency of the cells and the inhibition of de novo DNA synthesis induced by these substances aroused the question whether they also have genotoxic effects on V79 cells. Statistical analyses showed that sodium nitrite induced more 6-TG-resistant (6-TGr) mutants as compared to the untreated control. However, this elevation did not correspond to the level of inhibition of DNA synthesis determined during the followed period of time after the removal of the substance. Potassium sorbate and a combination thereof with sodium nitrite, in our experiments, had no mutagenic effects.

Animals↗

PubMed1982

[The effect of sodium nitrite on rats infected with avian sarcoma virus].

A potential effect of sodium nitrite was studied as exerted on carcinogenesis elicited by the avian sarcoma virus in the body of rats. In the case of the infection of the rats with indefective avian sarcoma virus B77 (Bratislava strain; ID50 10-25/0.1 ml) and i. p. inoculation of sodium nitrite, great mortality occurred already on the 20th day p. i. On the 125th day p. i. the cumulative mortality in this group was 76.92%; on the other hand, in the control groups (rats inoculated with sodium nitrite or avian sarcoma virus) no deaths occurred before this period. The rats infected with a double dose of the virus were not observed to show pronounced changes in mortality. It was only on the 125th day that cumulative mortality in the group of rats infected with the avian sarcoma virus and rats inoculated s. c. with sodium nitrite was 87.5% and in the group of animals which had only been infected with the virus the mortality was 64.26%. The patho-morphological changes were in keeping with the hitherto described changes in rats infected with the avian sarcoma virus. In the trial no effect of sodium nitrite on the patho-morphological changes induced by the avian sarcoma virus was observed.

Animals↗

PubMed1999

Biomonitoring of n-nitroso compounds, nitrite and nitrate in the urine of Egyptian bladder cancer patients with or without Schistosoma haematobium infection.

The excretion of nitrate, nitrite, apparent total N-nitroso compounds and volatile nitrosamines was measured in 24 hr urine from 61 Egyptians, divided into 4 groups: controls, Schistosoma haematobium-infected patients and bladder cancer patients with and without a history of schistosomal infection. Urinary nitrate in S. haematobium-infected patients was significantly higher than in the other 3 groups. Nitrite was below the detection limit of the method (</=0.015 microgram/mg creatinine) in all but one of the control samples. S. haematobium infection significantly increased urinary nitrite to 0.9 +/- 1.16 microgram/mg creatinine (mean +/- SD, p = 0. 001). In both bladder cancer groups, nitrite was about 20 times that in S. haematobium-infected patients without bladder cancer. Excretion of apparent total N-nitroso compounds paralleled that of nitrite. Overall, a good correlation was observed between these 2 variables (r = 0.71, p = 0.0001). N-nitrosodimethylamine was present in all the samples analyzed. S. haematobium infection significantly increased urinary N-nitrosodimethylamine level compared with that of controls (4.02 +/- 1.61 and 2.04 +/- 2.97 ng/mg creatinine, respectively, p = 0.01). Among cancer patients, N-nitrosodimethylamine was higher than in controls only in those with schistosomal infection. The presence of N-nitroso compounds and N-nitrosodimethylamine in the urine of S. haematobium-infected patients both before and after the development of cancer, and the observation that these compounds also occur in bladder cancer patients with no history of schistosomal infection, suggest that these compounds might have a role not only in the initiation of the carcinogenic process, but also in its progression.

Bacterial Infections↗

PubMed2000

Dietary exposure to nitrite and nitrosamines and risk of nasopharyngeal carcinoma in Taiwan.

Previous studies of nasopharyngeal carcinoma (NPC) have found elevated risks with higher consumption of salted fish and preserved foods, particularly during childhood. These foods can contain high levels of nitrosamines; however, most studies have not estimated exposure to nitrosamines directly. We conducted a case-control study in Taiwan to evaluate dietary intakes and NPC risk. A total of 375 cases (99% response rate) and 327 controls (88% response rate) were interviewed about their diet as an adult and at age 10 using a food-frequency questionnaire. We interviewed mothers of participants about their child's diet at age 10, age 3 and during weaning and the mother's diet while she was breast-feeding. Mothers of 96 cases and 120 controls were interviewed. Nitrosamine and nitrite levels were assigned to 66 foods based on published values. Intake of nitrosamines and nitrite as an adult was not associated with risk of NPC. High intakes of nitrosamines and nitrite during childhood and weaning were associated with increased risks of NPC for foods other than soy products. Adjusted odds ratios for the highest quartile were 2.2 [95% confidence interval (CI) 0.8-5.6] for age 10, 2.6 (95% CI 1.0-7.0) for age 3 and 3.9 (95% CI 1.4-10.4) for weaning diet. Intakes of nitrite and nitrosamines from soybean products during childhood and weaning were inversely associated with risk. Soybeans contain known inhibitors of nitrosation, and thus may explain the inverse association we observed. Our results suggest that nitrosamine and nitrite intake during childhood may play a role in the development of NPC.

Adult↗

PubMed2000

Simultaneous determination of bromide, nitrite and nitrate ions in seawater by capillary zone electrophoresis using artificial seawater as the carrier solution.

We describe capillary zone electrophoresis (CZE) for the simultaneous determination of bromide, nitrite and nitrate ions in seawater. Artificial seawater was adopted as the carrier solution to eliminate the interference of high concentrations of salts in seawater. The artificial seawater was free from bromide ion to enable the determination of bromide ion in a sample solution. For the purpose of reversing the electroosmotic flow (EOF), 3 mM cetyltrimethylammonium chloride (CTAC) was added to the carrier solution. A 100 microm ID (inside diameter) capillary was used to extend the optical path length. The limits of detection (LODs) for bromide, nitrite, and nitrate ions were 0.46, 0.072, and 0.042 mg/L (as nitrogen), respectively. The LODs were obtained at a signal to noise ratio (S/N) of 3. The values of the relative standard deviation (RSD) of peak area for these ions were 1.1, 1.5, and 0.97%. The RSDs of migration time for these ions were 0.61, 0.69, and 0.66%. Artificial seawater samples containing various concentrations of bromide, nitrite, and nitrate ions were analyzed by the method. The error was less than +/-12% even if the concentration ratio of bromide ion to nitrite or nitrate ion was 20-240. The proposed method was applied to the determination of bromide, nitrite, and nitrate ions in seawater samples taken from the surface and the seabed. These ions in other environmental waters such as river water and rainwater samples were also determined by ion chromatography (IC) as well as this method.

Bromides↗

PubMed2000

A highly sensitive method for the analysis of nitrite ions by capillary zone electrophoresis using water-soluble aminophenylporphyrin derivative as chromogenic reagent.

The water soluble 5-p-aminophenyl)-10,15,20-tris(p-sulfonatophenyl) porphyrin, 4, acts as an extremely efficient chromogenic reagent for the detection of very low amounts of nitrites. The amino group of porphyrin 4 reacts smoothly with nitrite in acidic conditions 0.2 M HCl) producing the corresponding diazo-porphyrin derivative which is stable and does not show any appreciable hydrolysis to phenol within 6 h. The reaction is carried out in the presence of 25 mM heptakis-(2,6-di-O-methyl)-beta-cyclodextrin that prevents precipitation of the protonated form of porphyrins 4 or 5 due to the formation of strong inclusion complexes. The capillary zone electrophoresis of the diazoporphyrin and amino-porphyrin mixture shows severe peak tailing. However, symmetrical peaks can be obtained by adding 5 mM beta-cyclodextrin to the background electrolyte (20 mM phosphate buffer, pH 7.0). Calibration curve for nitrite analysis is linear up to 0.25 mM nitrite and the detection limit (at a signal-to-noise ratio of 3) has been estimated to be a 1 microM (50 ppb) of nitrite concentration in aqueous solutions.

Chromogenic Compounds↗

PubMed2004

Metmyoglobin-catalyzed exogenous and endogenous tyrosine nitration by nitrite and hydrogen peroxide.

Metmyoglobin catalyzes the nitration of various phenolic compounds in the presence of nitrite and hydrogen peroxide. The reaction rate depends on the reactant concentrations and shows saturation behavior. Two competing paths are responsible for the reaction. In the first, myoglobin reacts according to a peroxidase-like cycle forming two active intermediates, which can induce one-electron oxidation of the substrates. The MbFe(IV)==O intermediate oxidizes nitrite to nitrogen dioxide, which, after reaction with the phenol or with a phenoxy radical, yields the nitrophenol. In the second mechanism, hydrogen peroxide reacts with iron-bound nitrite to produce an active nitrating species, which we assume to be a protein-bound peroxynitrite species, MbFe(III)--N(O)OO. The high nitrating power of the active species is shown by the fact that the catalytic rate constant is essentially independent of the redox properties of the phenol. The occurrence of one or other of these mechanisms depends on the nitrite concentration: at low [NO(2) (-)] the nitrating agent is nitrogen dioxide, whereas at high [NO(2) (-)] the peroxynitrite path is dominant. The myoglobin derivative that accumulates during turnover depends on the mechanism. When the path involving NO(2) (.) is dominant, the spectrum of the MbFe(IV)==O intermediate is observed. At high nitrite concentration, the Soret band appears at 416 nm, which we attribute to an iron-peroxynitrite species. The metMb/NO(2) (-)/H(2)O(2) system competitively nitrates the heme and the endogenous tyrosine at position 146 of the protein. Phenolic substrates protect Tyr146 from nitration by scavenging the active nitrating species. The exposed Tyr103 residue is not nitrated under the same conditions.

Catalysis↗

PubMed1991

Detection of coronary artery disease by vasodilator thallium imaging of the heart with amyl nitrite inhalation: a pilot study.

Thallium imaging of the heart using dipyridamole-induced coronary arteriolar vasodilation has proven to be an effective means of detecting significant coronary stenosis. However, intravenous dipyridamole has not yet been made available for general use. We therefore examined the feasibility of substituting amyl nitrite inhalation as an arteriolar vasodilator prior to thallium imaging. Seventeen patients, all of whom had catheterization-proven coronary stenosis, inhaled amyl nitrite for 2-5 min. Thallium was injected after 45-60 s of inhalation. Completion of inhalation was followed immediately by planar imaging. Of 6 patients who inhaled amyl nitrite for at least 4 min, 5 had moderate or severe image defects on immediate scans which completely resolved on delayed scans. Only 3 of 11 who inhaled amyl nitrite for 2 min or less prior to scanning had similarly positive tests. Overall sensitivity for significant stenosis was 8 of 17 (47%). Inhalation was well tolerated with only one episode of angina and hypotension. We conclude that amyl nitrite inhalation for at least 4 min may offer an effective and readily available alternative to intravenous dipyridamole for vasodilator imaging of the heart.

Administration, Inhalation↗

PubMed1997

Determination of nitrite and nitrate reduction by capillary ion electrophoresis.

Production of nitrates and nitrites is a common step in many methodologies used to measure nitric oxide (NO) and NO-derived products in biological fluids. We report conditions that allow the rapid separation and quantification of nitrite from nitrate ions in biological fluids by capillary ion electrophoresis (CIE). CIE can be used to directly quantify nitrites and nitrates near the millimolar range. To detect lower levels, we have used CIE to monitor the reduction of nitrites and nitrates to NO for chemiluminescence detection. For reduction reactions, we directly compared the ability of three commonly used agents--potassium iodide (KI), mercuric chloride (HgCl2) and vanadium chloride (VCl3)--to reduce nitrite and nitrate ions to NO. Nitrites/nitrates can be efficiently reduced to NO at 37 degrees C using vanadium chloride (100%) or HgCl2 (80%). However, these CE-derived conditions cannot simply be extrapolated to chemiluminescence measurements. Vanadium (III) yields high background in the photomultiplier that diminishes the sensitivity of chemiluminescence measurement to that outside of physiological ranges. We find that reactions carried out at 37 degrees C in 2 M HCl using HgCl2 is efficient using both techniques.

Electrophoresis, Capillary↗

PubMed2004

Determination of nitrate and nitrite in rat brain perfusates by capillary electrophoresis.

A fast and simple method for the direct, simultaneous detection of nitrite (NO(2) (-)) and nitrate (NO(3) (-)) in rat striatum has been developed using a capillary electrophoresis separation of low-flow push-pull perfusion samples. The method was optimized primarily for nitrite because nitrite is more important physiologically and is found at lower levels than nitrate. We obtained a complete separation of NO(2) (-) and NO(3) (-) in rat striatum within 1.5 min. Optimal CE separations were achieved with 20 mM phosphate, 2 mM cetyltrimethylammonium chloride (CTAC) buffer at pH 3.5. The samples were injected electrokinetically for 2 s into a 40 cm x 75 microm ID fused-silica capillary. The separation voltage was 10 kV (negative polarity), and the injection voltage was 16 kV (negative polarity). UV detection was performed at 214 nm. The limits of detection obtained at a signal-to-noise ratio (S/N) of 3 for nitrite and nitrate were 0.96 and 2.86 microM. This is one of the fastest separations of nitrite and nitrate of a biological sample ever reported. Interference produced by the high physiological level of chloride is successfully minimized by use of CTAC in the run buffer.

Animals↗

PubMed1975

Tumor induction in rats by feeding aminopyrine or oxytetracycline with nitrite.

Sprague-Dawley rats were given combinations of aminopyrine or oxytetracycline and sodium nitrite in drinking water. Of 30 animals receiving 0.1% (1,000 ppm) of aminopyrine and sodium nitrite for 30 weeks, 29 died with hemangioendothelial sarcomas of the liver. The same tumor caused death in 26 of 30 animals that received 0.025% (250 ppm) of both aminopyrine and sodium nitrite for 50 weeks. No animals in a control group of the same size that received 0.1% aminopyrine for 30 weeks developed this tumor, although one-half of them were still alive 2 years after the experiment was begun. After feeding a comparable dose (0.1%) of oxytetracycline and sodium nitrite for 60 weeks, liver tumors were present in 4 of 30 rats (3 hepatocellular tumors and 1 cholangioma). Since aminopyrine has been widely used for medicinal purposes in the human population, it is possible that many people have been exposed to a potent carcinogen (dimethylnitrosamine) by its formation in vivo. It is not certain whether the result of feeding oxytetracycline and sodium nitrite indicates significant carcinogenicity of this combination.

Adenoma, Bile Duct↗

PubMed1989

The inactivation of rhodanese by nitrite and inhibition by other anions in vitro.

Cyanide detoxification in mammals occurs, in part, by sulfur transfer by rhodanese to form the less toxic thiocyanate. Thiosulfate and nitrite are often used in combination for the treatment of cyanide intoxication. This report shows that nitrite can inhibit the rate of sulfur transfer by rhodanese in vitro. Nitrate, chloride, sulfate, and acetate were also examined as inhibitors. Inhibition by nitrite appeared to be more complex than for the other anions tested. Closer examination showed that nitrite can inactivate the sulfur-free rhodanese. Our observation leads to the suggestion that, in vivo, either rhodanese is maintained in its more stable sulfur-substituted form or cellular compartmentalization prevents inactivation by nitrite.

Animals↗

PubMed2002

Inhibitory effect of chlorophyllin on the frequency of micronuclei induced by sodium nitrite in mice.

In this report the potency of chlorophyllin (CHL) was evaluated to prevent two types of damage produced by nitrite in mice: the increase of micronucleated polychromatic erythrocytes (MNPE) and the bone marrow toxicity, measured as the index of polychromatic erythrocytes/normochromatic erythrocytes (PE/NE). The study was done in eight groups of male mice. The first three groups were administered orally for 4 days with sodium nitrite (10, 15 and 20 mg/kg), the daily administration with nitrite was followed by an intraperitoneal administration of CHL (4 mg/kg), three more groups were administered with the same amounts of nitrite, a seventh group of mice was treated with distilled water while another was treated with CHL (4 mg/kg). Our study produced two main results: (a) no bone marrow injury was induced by any of the tested chemicals, as indicated with the PE/NE index, and (b) CHL protected (as high as 44%) the MNPE produced in nitrite treated mice.

Administration, Oral↗

PubMed2006

Nitrite anions induce nitrosative deamination of peptides and proteins.

In the present study, reactions of sodium nitrite with proteins/peptides were characterized with mass spectrometry. The reaction generates two major products: replacement of the amino group by a hydroxyl group and formation of an alkene derivative by loss of a NH3 group at the N-terminus and the side chain of lysine residues of proteins/peptides. The reaction proceeds rapidly in weak acidic solution and at 37 degrees C in the presence of a millimolar concentration of nitrite, demonstrating that nitrite induces nitrosative deamination in proteins and peptides. The facile nitrite-induced modification of amino groups of protein/peptides changes the chemical nature of proteins and may have various applications in peptide synthesis, analytical chemistry, and protein engineering. It also provides information to enhance our understanding of functions of nitrite ions in biology and food preservation.

Anions↗

PubMed1993

A fluorometric assay for the measurement of nitrite in biological samples.

The increasing importance of nitric oxide synthase has been underscored by the elucidation of its role in a growing number of normal and pathophysiological processes. Therefore, techniques for detection of nitrite/nitrate, oxidation products of the enzymatic conversion of arginine to citrulline and nitric oxide, should serve as useful tools in defining the contribution of NO synthase to these processes. We have developed a rapid and sensitive fluorometric assay for quantification of nitrite/nitrate based upon the reaction of nitrite with 2,3-diaminonaphthalene to form the fluorescent product, 1-(H)-naphthotriazole. The assay can be used to detect 10 nM nitrite, making it 50-100 times more sensitive than the well-known Griess assay. Moreover, the assay is adaptable to a 96-well plate format, facilitating the handling of a large number of samples including conditioned media from cell culture or the nitrite generated by the purified enzyme. Nitrite/nitrate levels in blood can also be monitored using this assay when it is combined with a filtration step (to remove hemoglobin) followed by conversion of the nitrate to nitrite by nitrate reductase. Thus, this fluorometric method combines speed and sensitivity with the handling of a large number of samples for the quantification of nitrite generated from in vivo and in vitro sources.

2-Naphthylamine↗

PubMed1993

Nitrite production by stimulated human polymorphonuclear leukocytes supplemented with azide and catalase.

The formation of nitric oxide by human phagocytes as measured by nitrite production is controversial. We report here that nitrite production by phorbol myristate acetate (PMA)-stimulated human polymorphonuclear leukocytes (PMN) is considerably increased by the addition of azide and a further increase occurs when catalase also is added. Nitrite production by the PMN-PMA-azide-catalase system is unaffected by superoxide dismutase or monomethylarginine but is markedly reduced by the substitution of chronic granulomatous disease for normal neutrophils. The stimulated neutrophils could be replaced by the H2O2-generating enzyme system glucose-glucose oxidase. These findings suggest that nitrite production does not, in this instance, reflect nitric oxide synthase activity by human neutrophils but rather the catalase-catalyzed conversion of azide to nitrite in the presence of H2O2 generated by the stimulated PMN.

Azides↗

PubMed1995

Electrochemical studies on nitrite reductase towards a biosensor.

A c-type hexaheme nitrite reductase (NiR) isolated from nitrate-grown cells of Desulfovibrio desulfuricans (Dd) ATCC 27774 catalyses the six-electron reduction of nitrite to ammonia. Previous electrochemical studies demonstrated that a simple electrocatalytic mechanism can be applied to this system (Moreno, C., Costa, C., Moura, I., LeGall, J., Liu, M. Y., Payne, W. J., Van Dijk, C. and Moura, J. J. G. (1992) Eur.J.Biochem. 212, 79-86). Its substrate specificity, availability and stability under ambient conditions makes this enzymatic system a promising candidate for use in a biosensor device. An electrochemical study of gel-immobilized Dd NiR on a glassy carbon electrode revealed both enzymatic activity and amperometric response to nitrite. In this study it was observed that the catalytic current density is a function of the nitrite concentration in solution and follows a characteristic Michaelis-Menten-type substrate dependence. Such a biosensor device (NiR-electrode) bears the option to be used for analytical determination of nitrite in complex media.

Biosensing Techniques↗