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At least 19 recordsLinked to original sources
PubMed1977

Nitrate reduction to nitrite, a possible source of nitrite for growth of nitrite-oxidizing bacteria.

Growth yields and other parameters characterizing the kinetics of growth of nitrite-oxidizing bacteria are presented. These parameters were measured during laboratory enrichments of soil samples with added nitrite. They were then used to reanalyze data for nitrite oxidizer growth in a previously reported field study (M. G. Volz, L. W. Belser, M. S. Ardakani, and A. D. McLaren, J. Environ. Qual. 4:179-182, 1975), where nitrate, but not nitrite or ammonium, was added. In that report, analysis of the field data indicated that in unsaturated soils, the reduction of nitrate to nitrite may be a significant source of nitrite for the growth of nitrite oxidizers. A yield of 1.23 x 10(4) cells per mug of N was determined to be most appropriate for application to the field. It was determined that if nitrite came only from mineralized organic nitrogen via ammonium oxidation, 35 to 90% of the organic nitrogen would have had to have been mineralized to produce the growth observed. However, it is estimated that only about 2% of the organic nitrogen could have been mineralized during the growth period. Thus, it appears that another source of nitrite is required, the most likely being the reduction of nitrate to nitrite coupled to the oxidation of organic matter.

Nitrates↗
PubMed1979

[Analytical methods for nitrate and nitrite determination in foods. 3. Spectrophotometric determination of nitrate and nitrite using sulphanilic acid/1-naphylamine, and of nitrite using resorcinol/zirconium (IV) oxychloride].

The Nitrate content of foods may be determined by means of azo-dye coupling after reduction of the nitrate with the aid of active cadmium produced in the sample solution. An easy method for determining nitrite consists in the colorimetric estimation of a coloured chelate formed from nitrite, resorcinol and zirconium(IV) oxychloride.

1-Naphthylamine↗
PubMedDate not supplied

Nitrite adulteration of workplace urine drug-testing specimens. I. Sources and associated concentrations of nitrite in urine and distinction between natural sources and adulteration.

The active ingredient in the commercial workplace urine drug-testing adulterant, Klear, was previously determined to be nitrite ion. Nitrite adulteration compromises the confirmation of some drugs, notably the marijuana metabolite. A previously reported bisulfite step overcomes some nitrite adulteration, but it cannot do so in every case, which leaves the laboratory to report the specimen as not suitable for testing. Unlike many other adulterants, nitrite is found in normal urine at low concentrations. In order to defend a report of nitrite adulteration, it is necessary to provide evidence that the amount of nitrite in a workplace urine specimen could not arise by normal means. The objectives of this study were to identify all sources of nitrite in urine and the range of concentrations associated with these sources and to determine if nitrite adulteration can be supported based upon a quantitative result. The scientific literature was reviewed for internal and external sources of nitrite and their concentration ranges and are reported. The following specimens were obtained and nitrite concentrations measured by a spectrophotometric method: clinical specimens nitrite positive by test strip (< 15 micrograms/mL); specimens culture positive for nitrate-reducing microorganisms (< 36 micrograms/mL); specimens from patients on medications that may metabolize to nitrite (< 6 micrograms/mL); and drug-test specimens, both negative (< 130 micrograms/mL) and others that appeared to be adulterated with nitrite (range 1910-12,200 micrograms/mL, mean 5910). The literature and the nitrite measurements of this study indicate a substantial difference between concentrations from natural sources compared with adulteration. A quantitative measurement of nitrite by a well-structured assay can provide scientifically valid and forensically defensible proof of adulteration with a nitrite-containing substance.

Drug Contamination↗
PubMed2001

Blood plasma response and urinary excretion of nitrite and nitrate in milk-fed calves after oral nitrite and nitrate administration.

There is marked endogenous production of nitrate in young calves. Here we have studied the contribution of exogenous nitrate and nitrite to plasma concentrations and urinary excretion of nitrite and nitrate in milk-fed calves. In experiment 1, calves were fed 0 or 200 &mgr;mol nitrate or nitrite/kg(0.75) or 100 &mgr;mol nitrite plus 100 &mgr;mol nitrate/kg(0.75) with milk for 3 d. In experiment 2, calves were fed 400 &mgr;mol nitrate or nitrite/kg(0.75) with milk for 1 d. Plasma nitrate rapidly and comparably increased after feeding nitrite, nitrate or nitrite plus nitrate. The rise of plasma nitrate was greater if 400 than 200 &mgr;mol nitrate or nitrite/kg(0.75) were fed. Plasma nitrate decreased slowly after the 3-d administration of 200 &mgr;mol nitrate or nitrite/kg(0.75) and reached pre-experimental concentrations 4 d later. Urinary nitrate excretions nearly identically increased if nitrate, nitrite or nitrite plus nitrate were administered and excreted amounts were greater if 400 than 200 &mgr;mol nitrate or nitrite/kg(0.75) were fed. After nitrite ingestion plasma nitrite only transiently increased after 2 and 4 h and urinary excretion rates remained unchanged. Plasma nitrate concentration remained unchanged if milk was not supplemented with nitrite or nitrate. Nitrate concentrations were stable for 24 h after addition of nitrite to full blood in vitro, whereas nitrite concentrations decreased within 2 h. In conclusion, plasma nitrate concentrations and urinary nitrate excretions are enhanced dose-dependently by feeding low amounts of nitrate and nitrite, whereas after ingested nitrite only a transient and small rise of plasma nitrite is observed because of rapid conversion to nitrate.

Journal Article↗
PubMed1992

Characterization of Tn5 mutants deficient in dissimilatory nitrite reduction in Pseudomonas sp. strain G-179, which contains a copper nitrite reductase.

Tn5 was used to generate mutants that were deficient in the dissimilatory reduction of nitrite for Pseudomonas sp. strain G-179, which contains a copper nitrite reductase. Three types of mutants were isolated. The first type showed a lack of growth on nitrate, nitrite, and nitrous oxide. The second type grew on nitrate and nitrous oxide but not on nitrite (Nir-). The two mutants of this type accumulated nitrite, showed no nitrite reductase activity, and had no detectable nitrite reductase protein bands in a Western blot (immunoblot). Tn5 insertions in these two mutants were clustered in the same region and were within the structural gene for nitrite reductase. The third type of mutant grew on nitrate but not on nitrite or nitrous oxide (N2O). The mutant of this type accumulated significant amounts of nitrite, NO, and N2O during anaerobic growth on nitrate and showed a slower growth rate than the wild type. Diethyldithiocarbamic acid, which inhibited nitrite reductase activity in the wild type, did not affect NO reductase activity, indicating that nitrite reductase did not participate in NO reduction. NO reductase activity in Nir- mutants was lower than that in the wild type when the strains were grown on nitrate but was the same as that in the wild type when the strains were grown on nitrous oxide. These results suggest that the reduction of NO and N2O was carried out by two distinct processes and that mutations affecting nitrite reduction resulted in reduced NO reductase activity following anaerobic growth with nitrate.

Blotting, Southern↗
PubMed2002

Accumulations of nitrite and nitrate in the tissues of Penaeus monodon exposed to a combined environment of elevated nitrite and nitrate.

Penaeus monodon (11.86 +/- 0.63 g) exposed individually to six different nitrite and nitrate regimes [nitrite at 0.002 (control), 0.360, and 1.455 mM combined with nitrate at 0.005 (control) and 7.275 mM] in 25 ppt sea water were examined for the nitrite and nitrate concentrations in tissues and nitrite uptake and nitrate uptake after 24 h in 25.3 degrees C. In P. monodon following exposure to 1.455 mM nitrite only, nitrite levels increased by factors of 0.33, 1.05, 1.36, 1.79, 2.10, 2.16, 2.21, and 3.58 in muscle, hepatopancreas, gill, foregut, hemolymph, heart, eyestalk, and midgut, respectively, over the ambient nitrite level. In P. monodon, following exposure to combined solutions of 1.455 mM nitrite and 7.275 mM nitrate, nitrite levels were factors of 0.34, 1.05, 1.44, 1.86, 2.21, 2.30, 2.67, and 3.83 in muscle, hepatopancreas, gill, foregut, heart, hemolymph, eyestalk, and midgut, respectively, over the ambient nitrite levels, whereas nitrate levels were factors of 0.06, 0.11, 0.27, 0.29, 0.45, 0.51, 0.57, and 0.61 in muscle, hepatopancreas, foregut, heart, hemolymph, gill, midgut, and eyestalk, respectively, over the ambient nitrate levels. It is concluded that incorporation of nitrite is converted to nitrate in midgut, heart, hemolymph, foregut, and eyestalk, whereas incorporation of nitrate in tissues is converted to nitrite and accumulated in eyestalk when P. monodon are exposed to combined nitrite and nitrate environments.

Animals↗
PubMed1991

Regulation of nitrite uptake and nitrite reductase expression in Chlamydomonas reinhardtii.

Expression of nitrite uptake and nitrite reductase activities has been studied in Chlamydomonas reinhardtii under different nutritional conditions. Both activities were expressed at a low level in derepressed cells (with no nitrogen source) and at a high level in induced cells (with nitrate or nitrite). Nitrate was required for both activities to be maximally expressed. Ammonium-grown cells did not show nitrite uptake capability and had a basal nitrite reductase activity. Nitrite uptake but not nitrite reductase levels decreased very significantly in nitrate-induced cells subject to cycloheximide treatment, which suggests that protein(s) involved in the uptake are under a rapid turnover. Nitrite uptake expression was strongly inhibited by the presence of the glutamine synthetase inhibitor L-methionine-D,L-sulfoximine under either derepression or induction conditions, whereas that of nitrite reductase was not affected under the same conditions. Our results indicate that nitrite uptake expression is regulated primarily by ammonium, and that of nitrite reductase by both ammonium and ammonium derivative(s).

Ammonia↗
PubMed2000

Optical biosensing of nitrite ions using cytochrome cd1 nitrite reductase encapsulated in a sol-gel matrix.

Nitrite is an important human health and environmental analyte. As such, the European Union (EU) has imposed a limit for nitrite in potable water of 0.1 mg l-1 (2.18 microM). In order to develop an optical biosensing system for the determination of nitrite ions in environmental waters, cytochrome cd1 nitrite reductase has been extracted and purified from the bacterium Paracoccus pantotrophus. The protein has been spectroscopically characterised in solution and important kinetic parameters of nitrite reduction of the cytochrome cd1 enzyme, i.e., Km, Vmax and kcat have been determined. The influence of pH on the activity of the cytochrome cd1 has been investigated and the results suggest that this enzyme can be used for the determination of nitrite in the pH range 6-9. Biosensing experiments with the cytochrome cd1 in solution suggested that the decrease in intensity of the absorption band associated with the d1 haem (which is the nitrite binding site), at 460 nm, with increasing nitrite concentrations would enable the measurement of this analyte with the optimum limit of detection. The cytochrome cd1 has been encapsulated in a bulk sol-gel monolith with no structural changes observed and retention of enzymatic activity. The detection of nitrite ions in the range 0.075-1.250 microM was achieved, with a limit of detection of 0.075 microM. In order to increase the speed of response, a sol-gel sandwich thin film structure was formulated with the cytochrome cd1. This structure enabled the determination of nitrite concentrations within ca. 5 min. The sol-gel sandwich entrapped cytochrome cd1 enzyme was found to be stable for several months when the films were stored at 4 degrees C.

Biosensing Techniques↗
PubMed1981

Methylene blue inhibits coronary arterial relaxation and guanylate cyclase activation by nitroglycerin, sodium nitrite, and amyl nitrite.

Relaxation by nitroglycerin, sodium nitrite, and amyl nitrite of bovine coronary arterial smooth muscle was inhibited by the oxidant methylene blue. Methylene blue also inhibited activation of bovine coronary arterial soluble guanylate cyclase by nitroglycerin, which required addition of cysteine. At concentrations less than 10 mM, sodium nitrite required the addition of one of several thiols or ascorbate to activate guanylate cyclase from bovine coronary artery. Guanylate cyclase activation by large amounts (50 microL) of saturated amyl nitrite gas did not require, but was enhanced by, the addition of thiols or ascorbate. However, similar to sodium nitrite, guanylate cyclase activation by smaller amounts (5 microL) of saturated amyl nitrite gas did require the addition of one of various thiols or ascorbate. Methylene blue markedly inhibited guanylate cyclase activation by sodium nitrite in the presence of cysteine or ascorbate and similarly inhibited enzyme activation by amyl nitrite either in the absence or presence of cysteine or ascorbate. These data support the hypothesis that nitrates and nitrites relax vascular smooth muscle by stimulating cyclic GMP formation. The results further suggest that, similar to relaxation and guanylate cyclase activation by nitroso-containing compounds, relaxation and enzyme activation by nitrates and and nitrites may involve the formation of nitric oxide or complexes of nitric oxide as active intermediates.

Amyl Nitrite↗
PubMed2000

Accumulation of nitrite in the tissues of Penaeus monodon exposed to elevated ambient nitrite after different time periods.

Penaeus monodon (29.42 +/- 0.39 g) that had been exposed individually to 0.001 (control), 0.07, 0.36, 0.72, and 1.44 mM nitrite in 25 ppt sea water were examined for the nitrite accumulation in hemolymph, gill, eyestalk, heart, foregut, midgut, hepatopancreas, and muscle and nitrite uptake after 1, 3, 6, 12, 24, and 48 h, respectively. Concentration of nitrite in the tissues increased directly with ambient nitrite and exposure time except for muscle. P. monodon following 48-h exposure to 0.36 mM nitrite, nitrite concentration progressively increased from the muscle (0.40 micromol/g), hepatopancreas (1.24 micromol/g), gill (1.82 micromol/g), foregut (2.03 micromol/g), hemolymph (0.39 micromol/mL), heart (2.43 micromol/g), eyestalk (3.07 micromol/g), and to the midgut (4.14 micromol/g), which is 1.1, 3.4, 5.0, 5.6, 6.6, 6.8, 8.5, and 11.4 times the ambient nitrite concentration, respectively. It is concluded that when P. monodon is exposed to ambient nitrite, nitrite is immediately incorporated in the hemolymph and midgut via branchial chloride uptake of NO(2)(-), and accumulated in the tissues.

Animals↗
PubMed1986

The kinetic differences between sodium nitrite, amyl nitrite and nitroglycerin oxidation of hemoglobin.

The effect of sodium nitrite, amyl nitrite and nitroglycerin (glyceryl trinitrate) on the hemoglobin of adult erythrocytes was examined in vitro. Both amyl nitrite and nitroglycerin reacted immediately with oxyhemoglobin to effect oxidation into methemoglobin while sodium nitrite required an inductionary period (lag phase) prior to the reaction. Kinetic studies of the biomolecular rate law for each of the preceding reaction's reactionary periods (log phases) allowed rate constant calculations to be made. The values are 1.14 x 10(4) M-1 min-1, 7.45 x 10(4) M-1 min-1, and 3.50 x 10(1) M-1 min-1 for sodium nitrite, amyl nitrite and nitroglycerin, respectively. A comparison of the amyl nitrite and nitroglycerin rate constants reveals that amyl nitrite is approximately 2000-fold more toxic to oxyhemoglobin than nitroglycerin. These oxidant's effect on in vitro hemoglobin solutions are comparable since both reactions approximate to rectangular hyperbolae. Sodium nitrite reacts about 300-fold faster with oxyhemoglobin than does nitroglycerin. However, the sodium nitrite reaction proceeds in a sigmoidal fashion which makes a strict comparison between these compounds relative toxicities less clear cut.

Erythrocytes↗
PubMed1997

Structure of nitrite bound to copper-containing nitrite reductase from Alcaligenes faecalis. Mechanistic implications.

The structures of oxidized, reduced, nitrite-soaked oxidized and nitrite-soaked reduced nitrite reductase from Alcaligenes faecalis have been determined at 1.8-2.0 A resolution using data collected at -160 degrees C. The active site at cryogenic temperature, as at room temperature, contains a tetrahedral type II copper site liganded by three histidines and a water molecule. The solvent site is empty when crystals are reduced with ascorbate. A fully occupied oxygen-coordinate nitrite occupies the solvent site in crystals soaked in nitrite. Ascorbate-reduced crystals soaked in a glycerol-methanol solution and nitrite at -40 degrees C remain colorless at -160 degrees C but turn amber-brown when warmed, suggesting that NO is released. Nitrite is found at one-half occupancy. Five new solvent sites in the oxidized nitrite bound form exhibit defined but different occupancies in the other three forms. These results support a previously proposed mechanism by which nitrite is bound primarily by a single oxygen atom that is protonable, and after reduction and cleavage of that N-O bond, NO is released leaving the oxygen atom bound to the Cu site as hydroxide or water.

Alcaligenes↗
PubMed2003

Directing the mode of nitrite binding to a copper-containing nitrite reductase from Alcaligenes faecalis S-6: characterization of an active site isoleucine.

Unlike the heme cd(1)-based nitrite reductase enzymes, the molecular mechanism of copper-containing nitrite reductases remains controversial. A key source of controversy is the productive binding mode of nitrite in the active site. To identify and characterize the molecular determinants associated with nitrite binding, we applied a combinatorial mutagenesis approach to generate a small library of six variants at position 257 in nitrite reductase from Alcaligenes faecalis S-6. The activities of these six variants span nearly two orders of magnitude with one variant, I257V, the only observed natural substitution for Ile257, showing greater activity than the native enzyme. High-resolution (> 1.8 A) nitrite-soaked crystal structures of these variants display different modes of nitrite binding that correlate well with the altered activities. These studies identify for the first time that the highly conserved Ile257 in the native enzyme is a key molecular determinant in directing a catalytically competent mode of nitrite binding in the active site. The O-coordinate bidentate binding mode of nitrite observed in native and mutant forms with high activity supports a catalytic model distinct from the heme cd(1) NiRs. (The atomic coordinates for I257V[NO(2)(-)], I257L[NO(2)(-)], I257A[NO(2)(-)], I257T[NO(2)(-)], I257M[NO(2)(-)] and I257G[NO(2)(-)] AfNiR have been deposited in the Protein Data Bank [PDB identification codes are listed in Table 2].)

Alcaligenes↗
PubMed2000

The nrfA and nirB nitrite reductase operons in Escherichia coli are expressed differently in response to nitrate than to nitrite.

Escherichia coli possesses two distinct nitrite reductase enzymes encoded by the nrfA and nirB operons. The expression of each operon is induced during anaerobic cell growth conditions and is further modulated by the presence of either nitrite or nitrate in the cells' environment. To examine how each operon is expressed at low, intermediate, and high levels of either nitrate or nitrite, anaerobic chemostat culture techniques were employed using nrfA-lacZ and nirB-lacZ reporter fusions. Steady-state gene expression studies revealed a differential pattern of nitrite reductase gene expression where optimal nrfA-lacZ expression occurred only at low to intermediate levels of nitrate and where nirB-lacZ expression was induced only by high nitrate conditions. Under these conditions, the presence of high levels of nitrate suppressed nrfA gene expression. While either NarL or NarP was able to induce nrfA-lacZ expression in response to low levels of nitrate, only NarL could repress at high nitrate levels. The different expression profile for the alternative nitrite reductase operon encoded by nirBDC under high-nitrate conditions was due to transcriptional activation by either NarL or NarP. Neither response regulator could repress nirB expression. Nitrite was also an inducer of nirB and nrfA gene expression, but nitrate was always the more potent inducer by >100-fold. Lastly, since nrfA operon expression is only induced under low-nitrate concentrations, the NrfA enzyme is predicted to have a physiological role only where nitrate (or nitrite) is limiting in the cell environment. In contrast, the nirB nitrite reductase is optimally synthesized only when nitrate or nitrite is in excess of the cell's capacity to consume it. Revised regulatory schemes are presented for NarL and NarP in control of the two operons.

Anaerobiosis↗
PubMed1999

Ion chromatography of nitrite at the ppb level with photometric measurement of iodine formed by post-column reaction of nitrite with iodide.

The difficulty in ion-chromatographic determination of nitrite in aqueous solutions containing a high concentration of chloride arises mainly from incomplete resolution of the peaks for these anions on the separation column whose efficiency is not high. A photometric measurement of iodine formed by a reaction of nitrite with iodide has been found to make it possible to determine, chromatographically, trace amounts of nitrite without any interference from chloride; chloride does not oxidize iodide to produce iodine. The proposed method was based on the separation of nitrite from matrix anions on a silica-based anion-exchange column with a 1.5.10(-3) M phthalate eluent (pH 5.0), followed by photometric measurement of the iodine (as triiodide) formed via a post-column reaction of the separated nitrite with iodide. The optimal conditions for the post-column reaction were established by varying the concentrations of iodide, copper(II) and nitric acid in a post-column-reaction solution and the length of a reaction tube. A calibration graph for nitrite, plotted as peak heights versus concentrations, was linear up to 1.50.10(-5) M (690 ppb). The detection limit, defined at S/N = 3, was 1.00.10(-7) M (4.60 ppb) nitrite. The presence of chloride ions up to 0.01 M did not give any interference to the determination of nitrite. This method was successfully applied to the determination of nitrite in lake water, river water, sewage works water and snow samples without any pretreatment.

Chromatography, Ion Exchange↗
PubMed1993

The purification of a cd1-type nitrite reductase from, and the absence of a copper-type nitrite reductase from, the aerobic denitrifier Thiosphaera pantotropha; the role of pseudoazurin as an electron donor.

Thiosphaera pantotropha has been reported to contain a copper-type nitrite reductase on the basis that the copper chelator diethyldithiocarbamate inhibited the overall process of denitrification. It is now shown that nitrous oxide reduction is 100% inhibited by 10 mM diethyldithiocarbamate or 100 microM azide. We also found that both these inhibitors partially inhibited nitrite reduction in this organism. We purified the nitrite reductase of T. pantotropha and found that it was of the cytochrome cd1 type, contrary to the published report of it being a copper-type nitrite reductase. This is of importance since T. pantotropha is capable of aerobic nitrite reduction. The only detectable nitrite reductase in anaerobically or aerobically grown cells is the cd1 type. We also purified a small copper-containing protein, pseudoazurin. Pseudoazurin was found to be capable of donating electrons to the cd1-type nitrite reductase in vitro, and its copper centre was chelated by diethyldithiocarbamate. Since nitrite reduction is partially inhibited by diethyldithiocarbamate, it is thought that pseudoazurin is an electron donor to nitrite reductase in vivo.

Aerobiosis↗