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Showing papers on "Nitrite published in 1996"


Book ChapterDOI
01 Jan 1996
TL;DR: In this article, Bremner et al. defined the nonexchangeable NHt as the NHt in soil that cannot be replaced by a neutral potassium salt solution (SSSA, 1987), in contrast to NHt which is extractable at room temperature with such a solution.
Abstract: Most soils contain inorganic nitrogen (N) in the form of ammonium (NHt) and nitrate (NO)"). Nitrite (NOz) also may be present, but the amount is usually too small to warrant its determination, except in cases where NHt or NHt-forming fertilizers are applied to neutral or alkaline soils. Several other forms of inorganic N have been proposed as intermediates during microbial transformations of N in soils, including hydroxylamine (NH20H), hyponitrous acid (H2N20 2), and nitramide (NH2N02), but these compounds are thermodynamically unstable and have not been detected in soil. Until the 1950s, inorganic N was believed to account for <2% of total soil N, on the assumption that NHt and NO)" are completely recovered by extracting soil with a neutral salt solution. The validity of this assumption was challenged by the finding that some soils contain NHt in a form that is not extracted by exchange with other cations (e.g., Rodrigues, 1954; Dhariwal & Stevenson, 1958; Stevenson & Dhariwal, 1959; Bremner & Harada, 1959; Bremner, 1959; Schachtschabel, 1960, 1961; Young, 1962), and by estimates that the proportion of soil N in this form can exceed 50% for some subsurface soils (Stevenson & Dhariwal, 1959; Young, 1962). In such cases, NHt is said to be fixed, and fixed NHt has subsequently been defined as the NHt in soil that cannot be replaced by a neutral potassium salt solution (SSSA, 1987), such as 1 or 2 M KCI or 0.5 M K2S04, in contrast to exchangeable NHt, which is extractable at room temperature with such a solution. Existing information indicates that fixed NHt occurs largely, if not entirely, between the layers of 2: I-type clay minerals, particularly vermiculite and illite (hydrous mica), and that fixation results from entrapment of NHt in ditrigonal voids in the exposed surfaces upon contraction of the clay lattice (Nommik & Vahtras, 1982). The term, nonexchangeable NHt, has been used by Bremner (1965) and Keeney and Nelson (1982) in previous editions of this publication as a more precise alternative to fixed NHt. The same term is used in the present treatment, with specific reference to NHt determined by the method described in "Determination of Nonexchangeable Ammonium," which involves digestion with an HF-HCI solution following treatment of the soil with alkaline KOBr to remove exchangeable NHt and labile organic-N compounds.

2,810 citations


Journal ArticleDOI
TL;DR: An autotrophic, synthetic medium for the enrichment of anaerobic ammonium-oxidizing (Anammox) micro-organisms was developed and Acetylene, phosphate and oxygen were shown to be strong inhibitors of the Anammox activity.
Abstract: An autotrophic, synthetic medium for the enrichment of anaerobic ammonium-oxidizing (Anammox) micro-organisms was developed This medium contained ammonium and nitrite, as the only electron donor and electron acceptor, respectively, while carbonate was the only carbon source provided Preliminary studies showed that the presence of nitrite and the absence of organic electron donors were essential for Anammox activity The conversion rate of the enrichment culture in a fluidized bed reactor was 3 kg NH4 + m-3 d-1 when fed with 30 mM NH4 + This is equivalent to a specific anaerobic ammonium oxidation rate of 1000-1100 nmol NH4 +h-1 (mg volatile solids)-1 The maximum specific oxidation rate obtained was 1500 nmol NH4 +h-1 (mg volatile solids)-1 Per mol NH4 + oxidized, 0041mol CO2 were incorporated, resulting in a estimated growth rate of 0001 h-1 The main product of the Anammox reaction is N2, but about 10% of the N-feed is converted to NO3 - The overall nitrogen balance gave a ratio of NH4 --conversion to NO2 --conversion and NO3 --production of 1:1-31++006:022+002 During the conversion of NH4 + with NO2 -, no other intermediates or end-products such as hydroxylamine, NO and N2O could be detected Acetylene, phosphate and oxygen were shown to be strong inhibitors of the Anammox activity The dominant type of micro-organism in the enrichment culture was an irregularly shaped cell with an unusual morphology During the enrichment for Anammox micro-organisms on synthetic medium, an increase in ether lipids was observed The colour of the biomass changed from brownish to red, which was accompanied by an increase in the cytochrome content Cytochrome spectra showed a peak at 470 nm gradually increasing in intensity during enrichment

1,320 citations




Journal ArticleDOI
TL;DR: It is proposed that NO−2 reacts with HOCl by Cl+ transfer to form both cis- and trans-chlorine nitrite (Cl-ONO) and Cl-NO2 as intermediates that modify tyrosine by either direct reaction or after decomposition to reactive free and solvent-caged Cl· and ·NO1 as reactive species.

436 citations


Journal ArticleDOI
TL;DR: The products noted above account quantitatively for virtually all of the GSNO nitrogen consumed during the reaction, and it is now possible to construct a complete set of pathways for the complex transformations arising from GSNO + GSH.
Abstract: S-Nitrosothiols have generated considerable interest due to their ability to act as nitric oxide (NO) donors and due to their possible involvement in bioregulatory systems-e.g., NO transfer reactions. Elucidation of the reaction pathways involved in the modification of the thiol group by S-nitrosothiols is important for understanding the role of S-nitroso compounds in vivo. The modification of glutathione (GSH) in the presence of S-nitrosoglutathione (GSNO) was examined as a model reaction. Incubation of GSNO (1 mM) with GSH at various concentrations (1-10 mM) in phosphate buffer (pH 7.4) yielded oxidized glutathione, nitrite, nitrous oxide, and ammonia as end products. The product yields were dependent on the concentrations of GSH and oxygen. Transient signals corresponding to GSH conjugates, which increased by one mass unit when the reaction was carried out with 15N-labeled GSNO, were identified by electrospray ionization mass spectrometry. When morpholine was present in the reaction system, N-nitrosomorpholine was formed. Increasing concentrations of either phosphate or GSH led to lower yields of N-nitrosomorpholine. The inhibitory effect of phosphate may be due to reaction with the nitrosating agent, nitrous anhydride (N2O3), formed by oxidation of NO. This supports the release of NO during the reaction of GSNO with GSH. The products noted above account quantitatively for virtually all of the GSNO nitrogen consumed during the reaction, and it is now possible to construct a complete set of pathways for the complex transformations arising from GSNO + GSH.

314 citations


Journal ArticleDOI
TL;DR: In a dynamic aerobic-anaerobic culture of A. faecalis TUD, a semisteady state in which most of the N2O production took place after the transition from anaerobic to aerobic conditions was obtained, the influence of different oxygen concentrations and oxygen fluctuations on denitrification was studied.
Abstract: Nitrous oxide can be a harmful by-product in nitrogen removal from wastewater. Since wastewater treatment systems operate under different aeration regimens, the influence of different oxygen concentrations and oxygen fluctuations on denitrification was studied. Continuous cultures of Alcaligenes faecalis TUD produced N2O under anaerobic as well as aerobic conditions. Below a dissolved oxygen concentration of 5% air saturation, the relatively highest N2O production was observed. Under these conditions, significant activities of nitrite reductase could be measured. After transition from aerobic to anaerobic conditions, there was insufficient nitrite reductase present to sustain growth and the culture began to wash out. After 20 h, nitrite reductase became detectable and the culture started to recover. Nitrous oxide reductase became measurable only after 27 h, suggesting sequential induction of the denitrification reductases, causing the transient accumulation of N2O. After transition from anaerobic conditions to aerobic conditions, nitrite reduction continued (at a lower rate) for several hours. N2O reduction appeared to stop immediately after the switch, indicating inhibition of nitrous oxide reductase, resulting in high N2O emissions (maximum, 1.4 mmol liter-1 h-1). The nitrite reductase was not inactivated by oxygen, but its synthesis was repressed. A half-life of 16 to 22 h for nitrite reductase under these conditions was calculated. In a dynamic aerobic-anaerobic culture of A. faecalis, a semisteady state in which most of the N2O production took place after the transition from anaerobic to aerobic conditions was obtained. The nitrite consumption rate in this culture was equal to that in an anaerobic culture (0.95 and 0.92 mmol liter-1 h-1, respectively), but the production of N2O was higher in the dynamic culture (28 and 26% of nitrite consumption, respectively).

281 citations


Journal ArticleDOI
TL;DR: In this paper, Nitrification potentials were determined in soil slurries of pH 4 and 6 from the profiles of six peat soils, and the N2O fluxes correlated positively with the numbers of nitrite oxidizers, nitrification potential, N, P and Ca content and pH of the soil and negatively with the level of water table (expressed as negative values).
Abstract: Peat soils with high nitrogen content are potential sources of nitrous oxide (N2O). Fluxes of nitrous oxide were measuredin situ on nine virgin and ten drained peatlands of different hydrology and nutrient status. Numbers of nitrifying bacteria were estimated in different layers of the peat profiles with a most-probable-number technique. Nitrification potentials were determined in soil slurries of pH 4 and 6 from the profiles of six peat soils. Many virgin peatlands showed low N2O uptake. Lowering of the water table generally increased the average fluxes of N2O from the soils, although more in minerotrophic (nutrient rich) than in ombrotrophic (nutrient poor) sites. Ammonium oxidizing bacteria were found on only two sites but nitrite oxidizers were detected in almost all peat profiles. More nitrite oxidizers were found in drained than in virgin peat profiles. Nitrification was enhanced after lowering of the water table in minerotrophic peat but not in ombrotrophic peat. The N2O fluxes correlated positively with the numbers of nitrite oxidizers, nitrification potential, N, P and Ca content and pH of the soil and negatively with the level of water table (expressed as negative values) and K content of the soil.

266 citations


Journal ArticleDOI
TL;DR: In this article, the authors measured chemoautotrophic bacterial nitrification rates in the lower euphotic zone at the North Pacific Time-series Station ALOHA using low-level chemical assays and inhibitor-sensitive radiocarbon uptake experiments.
Abstract: We measured chemoautotrophic bacterial nitrification rates in the lower euphotic zone at the North Pacific Time-series Station ALOHA using low-level chemical assays and inhibitor-sensitive radiocarbon uptake experiments. These measurements were compared with independent nitrification rate estimates based on nitrous oxide distributions, nitrate assimilation rates based on nitrate changes during an in situ incubation, and historical estimates of nitrification and nitrate assimilation from this region. Ammonium oxidation rates ranged from 1.0 to 137.4 hmol m-3 d-l, and nitrite oxidation rates varied from undetectable to 138.0 pmol m-3 d-l. Conservative estimates of depth-integrated euphotic zone nitrification rates from the complete three-cruise data set were 0.69 mmol rnd2 d-l for nitrite oxidation and 1.64 mmol m-2 d-l for ammonium oxidation. The highest nitrification rates were found below the primary nitrite maximum, suggesting a significant contribution of euphotic zone ammonium oxidation to the nitrite pool below but not within this feature. A mass balance of nitrous oxide indicates that this gas is produced within the euphotic zone at a rate of 1.68-7.94 pmol m-2 d-l. The nitrous oxide production rate provides an independent estimate of the total euphotic zone nitrification rate in the range of 0.34-l .59 mmol m-2 d-l. We estimate that the total euphotic zone nitrification rate is 47-142% of the concurrent nitrate assimilation rate, indicating that nitrification in the euphotic zone is an important source of regenerated nitrate. Nitrification, the microbiologically mediated oxidation of ammonium to nitrite and nitrite to nitrate, is a key process in the global nitrogen cycle (Ward 1986). In the marine environment, the vertical flux into the cuphotic zone of nitrate regenerated by nitrification in deep water is considered crucial to ecosystem stability through its support of new primary photosynthetic production (Eppley and Peterson 1979). However, nitrifying bacteria are also active within the euphotic zone, especially within the primary nitrite maximum (Olson 198 1

256 citations


Journal ArticleDOI
TL;DR: It is concluded that hmp expression is negatively regulated by Fnr under anaerobic conditions and that additional regulatory mechanisms are involved in the responses to oxygen, nitrogen compounds, and iron availability.
Abstract: Escherichia coli possesses a soluble flavohemoglobin, with an unknown function, encoded by the hmp gene. A monolysogen containing an hmp-lacZ operon fusion was constructed to determine how the hmp promoter is regulated in response to heme ligands (O2, NO) or the presence of anaerobically utilized electron acceptors (nitrate, nitrite). Expression of the phi (hmp-lacZ)1 fusion was similar during aerobic growth in minimal medium containing glucose, glycerol, maltose, or sorbitol as a carbon source. Mutations in cya (encoding adenylate cyclase) or changes in medium pH between 5 and 9 were without effect on aerobic expression. Levels of aerobic and anaerobic expression in glucose-containing minimal media were similar; both were unaffected by an arcA mutation. Anaerobic, but not aerobic, expression of phi (hmp-lacZ)1 was stimulated three- to four-fold by an fnr mutation; an apparent Fnr-binding site is present in the hmp promoter. Iron depletion of rich broth medium by the chelator 2'2'-dipyridyl (0.1 mM) enhanced hmp expression 40-fold under anaerobic conditions, tentatively attributed to effects on Fnr. At a higher chelator concentration (0.4 mM), hmp expression was also stimulated aerobically. Anaerobic expression was stimulated 6-fold by the presence of nitrate and 25-fold by the presence of nitrite. Induction by nitrate or nitrite was unaffected by narL and/or narP mutations, demonstrating regulation of hmp by these ions via mechanisms alternative to those implicated in the regulation of other respiratory genes. Nitric oxide (10 to 20 microM) stimulated aerobic phi (hmp-lacZ)1 activity by up to 19-fold; soxS and soxR mutations only slightly reduced the NO effect. We conclude that hmp expression is negatively regulated by Fnr under anaerobic conditions and that additional regulatory mechanisms are involved in the responses to oxygen, nitrogen compounds, and iron availability. Hmp is implicated in reactions with small nitrogen compounds.

254 citations


Journal ArticleDOI
TL;DR: Generation of salivary nitrite from dietary nitrate may provide significant protection against gut pathogens in humans, and addition of SCN-, but not that of CI-, increased the antibacterial activity.
Abstract: Dietary intake of nitrate generates salivary nitrite, which is acidified in the stomach, leading to a number of reactive intermediates of nitrogen, among which are the potentially carcinogenic N-nitrosamines. Acidified nitrite, however, also has antimicrobial activity which coincides with the formation of nitric oxide. The present study examines the antimicrobial effect in vitro of acidified nitrite on Salmonella enteritidis, Salmonella typhimurium, Yersinia enterocolitica, Shigella sonnei, and Escherichia coli O157. First-order regression plots showed a linear inverse relationship of log-transformed proton and nitrite concentrations with MICs and MBCs after 30 min, 2 h, and 24 h of exposure (P S. enteritidis > S. typhimurium = Shigella sonnei > E. coli O157 (P < 0.05). Addition of SCN-, but not that of CI-, increased the antibacterial activity (paired t testing, P < 0.001). Generation of salivary nitrite from dietary nitrate may provide significant protection against gut pathogens in humans.

Journal ArticleDOI
TL;DR: Induction and repression of denitrification activity were studied in a continuous culture of Paracoccus denitrificans during changes from aerobic to anaerobic growth conditions and vice versa, suggesting different modes of regulation for the three genes.
Abstract: Induction and repression of denitrification activity were studied in a continuous culture of Paracoccus denitrificans during changes from aerobic to anaerobic growth conditions and vice versa. The denitrification activity of the cells was monitored by measuring the formation of denitrification products (nitrite, nitric oxide, nitrous oxide, and dinitrogen), individual mRNA levels for the nitrate, nitrite, and nitrous oxide reductases, and the concentration of the nitrite reductase enzyme with polyclonal antibodies against the cd1-type nitrite reductase. On a change from aerobic to anaerobic respiration, the culture entered an unstable transition phase during which the denitrification pathway became induced. The onset of this phase was formed by a 15- to 45-fold increase of the mRNA levels for the individual denitrification enzymes. All mRNAs accumulated during a short period, after which their overall concentration declined to reach a stable value slightly higher than that observed under aerobic steady-state conditions. Interestingly, the first mRNAs to be formed were those for nitrate and nitrous oxide reductase. The nitrite reductase mRNA appeared significantly later, suggesting different modes of regulation for the three genes. Unlike the mRNA levels, the level of the nitrite reductase protein increased slowly during the anaerobic period, reaching a stable value about 30 h after the switch. All denitrification intermediates could be observed transiently, but when the new anaerobic steady state was reached, dinitrogen was the main product. When the anaerobic cultures were switched back to aerobic respiration, denitrification of the cells stopped at once, although sufficient nitrite reductase was still present. We could observe that the mRNA levels for the individual denitrification enzymes decreased slightly to their aerobic, uninduced levels. The nitrite reductase protein was not actively degraded during the aerobic period.

Journal ArticleDOI
TL;DR: In this article, aqueous nitrate solution was photolysed at 254 nm in the absence of oxidizable additives, in the presence of methanol or propan-2-ol and oxygen and in the case of cyclopentane under anaerobic conditions.
Abstract: Aqueous nitrate solutions were photolysed at 254 nm in the absence of oxidizable additives, in the presence of methanol or propan-2-ol and oxygen and in the presence of cyclopentane under anaerobic conditions. The main nitrogen-containing products are nitrite and peroxynitrite. The quantum yields depend on the pH, nitrate concentration, nature of the additive and the light intensity. The intrinsic nitrite yield in alkaline solutions could not be determined directly because, under the conditions of the nitrite assay, the accompanying peroxynitrite decomposes to form nitrite and nitrate; it is smaller than the apparent nitrite yield. In the acidic (pH 4–7) range, the intrinsic nitrite quantum yield is equal to the apparent nitrite yield because there is no buildup of peroxynitrite under these conditions. The apparent nitrite quantum yield increases from 0.01 (no oxidizable additive) to approximately 0.03 (cyclopentane (millimolar range), oxygen free) to 0.06 (methanol (millimolar range), air saturated). At pH 13 and in the absence of oxidizable additives, the apparent nitrite quantum yield increases to about 0.1, whereas from material balance considerations the intrinsic nitrite quantum yield is estimated to be 0.06, twice the oxygen quantum yield of 0.03. Spectrophotometrically, peroxynitrite is detected in the alkaline range only, because its protonated form is unstable. In the absence of oxidizable additives, the quantum yield of peroxynitrite is about 0.1, i.e. only about two-thirds of the quantum yield in the presence of oxidizable additives. Mechanistic considerations on the basis of the pH dependence of the quantum yields of the products nitrite, peroxynitrite and oxygen, as well as their dependence on the kind of additive, indicate that the decisive factor of photolysis in the absence of additives is the formation of the nitric oxide peroxyl radical, ONOO, formed by reaction of peroxynitrite with the primarily generated OH radical. The decay of ONOO is the source of O2 in this system. Nitric oxide, NO, the other fragment of this decay reaction, reacts with nitrogen dioxide, which is one of the primarily formed intermediates. The latter reaction is one of the pathways to the product nitrite, particularly in the alkaline range. The formation of NO during photolysis has been verified by electron spin resonance (ESR) spectroscopic detection of the nitroxide 1,1,3,3-tetramethyl-isoindolin-2-oxyl, the NO adduct to 7,7,8,8-tetramethyl-o-quinodimethane. Of the three primary processes discussed in the literature, we conclude that reactions (1) and (2) occur with quantum yields of approximately 0.09 and 0.1 respectively NO3−+hv→NO2+O−(O−+H2O→OH+OH−)(1)NO3−+hv→ONOO−(2) It appears that none of the peroxynitrite anion is formed in a cage reaction through the recombination of the primary fragments from reaction (1). The primary process shown in reaction (3) is of relatively minor importance, with a quantum yield of no more than 0.001 NO3−+hv→NO2−+O(3) In the presence of methanol (or propan-2-ol) and oxygen under acidic conditions, formaldehyde (or acetone) is formed in an amount equivalent to nitrite via peroxyl radical reactions (quantum yield of approximately 0.06 for both alcohols). In the alkaline range, the apparent formaldehyde quantum yield decreases with increasing pH, while formic acid is produced in increasing amounts. The formation of formic acid is ascribed to the reaction of peroxynitrite anion with photolytically generated formaldehyde. The acetone quantum yield does not decrease with increasing pH over the whole alkaline pH range. In the presence of cyclopentane under oxygen-free conditions, apart from nitrite (and peroxynitrite when alkaline), the compounds nitrocyclopentane, cyclopentyl nitrate, cyclopentene, cyclopentanol and cyclopentanone are produced. The formation of the organic nitrogen compounds leads to an increase in the pH as photolysis proceeds. This pH shift is particularly pronounced in the neutral range.

Journal ArticleDOI
TL;DR: NOS is present in human spermatozoa and that eNOS and bNOS are abundant in normozoospermic samples, and nitric oxide (at endogenous concentrations) appears to be necessary for adequate sperm motility.
Abstract: The aim of this study was to investigate the presence of nitric oxide synthase (NOS) and the production of nitric oxide (NO) by human spermatozoa. Immunoreactivity was examined using a polyclonal antibody raised against porcine cerebellar nitric oxide synthase and monoclonal endothelial (elMOS) and brain (bNOS) antibodies. Using each antibody, NOS was observed localized in the head and midpiece regions of the spermatozoon. Immunofluorescence observed for eNOS and bNOS was more intense in normozoosperm ic samples. Sperm motility was assessed by computer-assi sted semen analysis (CASA) in the presence and absence of N G-nitro-L-arginine methyl ester (L-NAME; 10~5M), an NO synthesis inhibitor or tumour necrosis factor (TNF)-a (20 lU/ml), a superoxide inducer. In the presence of L-NAME, percentage progressive motility, average path velocity (VAP), straight line velocity (VSL) and curvilinear velocity (VCL) were significantly reduced after 30 min. Sperm viability was not decreased by TNFoc or L-NAME. The accumulation of nitrite (the stable end-product of the NOS/NO pathway) by spermatozoa was measured using the Griess reaction. After 8 h, nitrite concentrations were lower in asthenozoospermic compared to normozoosperm ic samples. In the presence of TNFcc, nitrite accumulation was significantly reduced in normozoosperm ic samples. We conclude that NOS is present in human spermatozoa and that eNOS and bNOS are abundant in normozoospermic samples. Nitric oxide (at endogenous concentrations) appears to be necessary for adequate sperm motility.

Journal ArticleDOI
TL;DR: Although most anaerobically expressed genes are subject to transcription control, none of them are totally switched off, so bacteria can respond equally rapidly whether times get better with the arrival of oxygen, or get worse when the nitrate is depleted.
Abstract: Anaerobic metabolism of the simplest, best understood enteric bacteria such as Escherichia coli is unexpectedly complex. Recent studies of the biochemistry and genetics of nitrate reduction via nitrite to ammonia by enteric bacteria have provided insights into the reasons for this complexity. An NADH-dependent nitrite reductase in the cytoplasm works in partnership with the respiratory nitrate reductase on the cytoplasmic side of the membrane when nitrate is abundant. There is also an electrogenic, formate-dependent nitrite reductase ready to work in partnership with a periplasmic nitrate reductase when nitrite is available but nitrate is scarce. A third E. coli nitrate reductase, NarZYWV, and the poorly expressed formate dehydrogenase O possibly facilitate rapid adaptation to oxygen starvation pending the synthesis of the major respiratory formate-nitrate oxidoreductase. Although most anaerobically expressed genes are subject to transcription control, none of them are totally switched off. This enables the bacteria to be ready for a change in fortune: when growing anaerobically with nitrate, they can respond equally rapidly whether times get better with the arrival of oxygen, or get worse when the nitrate is depleted. Far from being redundant, the complexity is essential for survival in a changing environment.

Journal ArticleDOI
TL;DR: In this article, the quantum yields of phenol and nitrate, produced by photodecomposition in aqueous solutions of NO2- and HNO2 in the presence of benzene as scavenger for OH radicals, have been determined as a function of wavelength between 280 and 390 nm.
Abstract: Quantum yields of phenol and nitrate, produced by photodecomposition in aqueous solutions of NO2- and HNO2 in the presence of benzene as scavenger for OH radicals, have been determined as a function of wavelength between 280 and 390 nm. The production of phenol was used to calculate primary OH quantum yields. For NO2- photolysis at pH 6 Φ1(OH) was found to decrease with increasing wavelength from 0.069 ± 0.008 at 280 nm to 0.022 ± 0.004 at 390 nm, in agreement with previous data. The OH quantum yield Φ2(OH) for the photolysis of HNO2 at pH 2 was essentially constant over the entire wavelength range with Φ2 = 0.35 ± 0.02 (2σ). Quantum yields for NO3- are comparable in magnitude to those of phenol, indicating that NO as primary product is largely oxidized to nitrate. The most likely conversion processes are reactions of NO with O2- (pH 6), the latter resulting from the oxidation of benzene, to form peroxynitrous acid, which undergoes thermal decomposition, and of NO2 with HO2 (pH 2) to form peroxynitric aci...

Journal ArticleDOI
TL;DR: In this article, the abilities of zero-valent iron powder and hydrogen with a palladium catalyst (H2/Pd-alumina) to hydrodehalogenate 1,2-dibromo-3-chloropropane (DBCP) to propane under water treatment conditions (ambient temperature and circumneutral pH) were compared.

Journal ArticleDOI
TL;DR: It is proposed that NO generation from skin is dependent on bacterial nitrate reduction to nitrite and subsequent reduction by acidification, and has a physiologic role in the inhibition of infection by pathogenic fungi and other susceptible microorganisms.

Journal ArticleDOI
TL;DR: The authors' study using concomitant measurement of plasma and urine nitrate and nitrite suggests a reduced production of nitric oxide in women with preeclampsia compared with normal pregnant women.

Journal ArticleDOI
TL;DR: Differences in intermediate nitrite accumulation are proposed to be caused by differences in electron flow to nitrate and nitrite reductases during oxidation of either acetate or butyrate.
Abstract: Intermediate nitrite accumulation during denitrification by Pseudomonas stutzeri isolated from a denitrifying fluidized bed reactor was examined in the presence of different volatile fatty acids. Nitrite accumulated when acetate or propionate served as the carbon and electron source but did not accumulate in the presence of butyrate, valerate, or caproate. Nitrite accumulation in the presence of acetate was caused by differences in the rates of nitrate and nitrite reduction and, in addition, by competition between nitrate and nitrite reduction pathways for electrons. Incubation of the cells with butyrate resulted in a slower nitrate reduction rate and a faster nitrite reduction rate than incubation with acetate. Whereas nitrate inhibited the nitrite reduction rate in the presence of acetate, no such inhibition was found in butyrate-supplemented cells. Cytochromes b and c were found to mediate electron transport during nitrate reduction by the cells. Cytochrome c was reduced via a different pathway when nitrite-reducing cells were incubated with acetate than when they were incubated with butyrate. Furthermore, addition of antimycin A to nitrite-reducing cells resulted in partial inhibition of electron transport to cytochrome c in acetate-supplemented cells but not in butyrate-supplemented cells. On the basis of these findings, we propose that differences in intermediate nitrite accumulation are caused by differences in electron flow to nitrate and nitrite reductases during oxidation of either acetate or butyrate.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated operating variables of the electrochemical method including the current input, pH, conductivity, buffer solution and initial nitrite and ammonia concentrations were considered to determine their respective effect on the efficiency of the removal of Nitrite and Ammonia.

Journal ArticleDOI
TL;DR: Nitric oxide is produced by human coronary microvessels, that nitric oxide production may be reduced but certainly not increased in microvessel from the failing human heart, and that there is active local kinin generation in these blood vessels.
Abstract: Background The goal of this study was to define the regulation of nitric oxide release by coronary microvessels from the failing and nonfailing human heart and to determine the role of local kinin production in the elaboration of nitric oxide by human coronary microvascular endothelium. Methods and Results Ten hearts from humans with end-stage heart failure and two hearts from patients without heart failure were harvested at the time of orthotopic cardiac transplantation. Microvessels were sieved and the production of nitrite was determined by the Griess reaction. Microvessels were incubated in the presence of agonists for nitric oxide production (acetylcholine and bradykinin), which caused dose-dependent increases in nitrite, a response that was blocked by N G-nitro-l-arginine methyl ester and receptor-specific antagonists (atropine and HOE 140, respectively). In addition, the production of nitrite by microvessels from the failing heart appeared to be less than that produced by microvessels from the nonfailing heart. Incubation with norepinephrine or the α2-adrenergic agonist BHT 920 also caused dose-dependent increases in nitrite production, which were blocked by the B2-receptor antagonist HOE 140. This implicated local kinin synthesis as an intermediate step in the production of nitric oxide in response to α2-adrenoceptor stimulation. The production of nitric oxide was also prevented by the addition of serine protease inhibitors, which blocked the action of local kallikrein, again suggesting a role for local kinin synthesis. Conclusions Our results indicate that nitric oxide is produced by human coronary microvessels, that nitric oxide production may be reduced but certainly not increased in microvessels from the failing human heart, and that there is active local kinin generation in these blood vessels.

Journal ArticleDOI
TL;DR: In this article, a detailed study on the acceleration mechanism of the above-mentioned oxidation was performed at pH values between 3.0 and 5.6 at various freezing rates, by different freezing methods, and with and without additional salts.
Abstract: The oxidation of nitrite by dissolved oxygen to form nitrate is known to be accelerated ca. 105 times by the freezing of the aqueous solution.1 Here we report a detailed study on the acceleration mechanism of the above-mentioned oxidation. The reaction was studied at pH values between 3.0 and 5.6 at various freezing rates, by different freezing methods, and with and without additional salts. The effect of freezing which induced concentration (freeze concentration) of reactants into the unfrozen bulk solution was too small to explain the acceleration factor of ca. 105. Nitrate formations were completely prevented by addition of salts, such as NaCl and KCl, which make the freezing potential of ice negative, while the reaction was not affected by addition of salts, such as Na2SO4 and NH4Cl, which make the freezing potential of ice positive. When a sample solution was frozen in such a way as to form a single crystal of ice, most nitrite was exclusively liberated from the ice to the gas phase. This observation...

Journal ArticleDOI
TL;DR: In this paper, the authors extended Schulthess et al.'s model with the consumption of organic substrate and with nitrification to predict the nitrous oxide (N2O) accumulation in continuously fed full scale waste water treatment plants.

Journal ArticleDOI
TL;DR: In this paper, the effects of electrode materials, cell design, and other experimental parameters have been investigated for the reduction of nitrate and nitrite in a synthetic waste mixture in a divided laboratory electrochemical flow cell using a lead cathode, Nafion® 417 cation exchange membrane and oxygen evolving DSA® or platinum clad niobium anode at a current density of 500 mA cm−2 and a temperature of 70°C.
Abstract: Sodium nitrate and nitrite are major components of alkaline nuclear waste streams and contribute to environmental release hazards. The electrochemical reduction of these materials to gaseous products has been studied in a synthetic waste mixture. The effects of electrode materials, cell design, and other experimental parameters have been investigated. Lead was found to be the best cathode material in terms of current efficiency for the reduction of nitrate and nitrite in the synthetic mix. The current efficiency for nitrite and nitrate removal is improved in divided cells due to the elimination of anodic oxidation of nitrite. Operation of the divided cells at high current densities (300–600 mA cm−2) and high temperatures (80°C) provides more efficient reduction of nitrite and nitrate. Nearly complete reduction of nitrite and nitrate to nitrogen, ammonia, or nitrous oxide was demonstrated in 1000 h tests in a divided laboratory electrochemical flow cell using a lead cathode, Nafion® 417 cation exchange membrane, and oxygen evolving DSA® or platinum clad niobium anode at a current density of 500 mA cm−2 and a temperature of 70° C. Greater than 99% of the nitrite and nitrate was removed from the synthetic waste mix batch in the 1000 h tests at an overall destruction efficiency of 55%. The process developed shows promise for treating large volumes of waste.

Journal ArticleDOI
TL;DR: Intakes of dietary nitrate, nitrite and NDMA estimated on an individual level are suggested to be useful in evaluating the health effects of these compounds in epidemiological studies.
Abstract: Concern about potential health hazards of nitrate, nitrite and N-nitroso compounds necessitates calculations of exposures to these compounds and their distribution in normal populations. This study describes dietary intake of nitrate (NO3-), nitrite (NO2-) and N-nitrosodimethylamine (NDMA) among 5304 adult men and 4750 women, who participated in the Finnish Mobile Clinic Health Examination Survey in 1967-72. Food consumption data for each individual over the preceding year were collected by a dietary history interview. Intakes of nitrate, nitrite and NDMA from vegetables, fruits, cheese, meat and fish products were calculated using available values mainly derived from Finland and other countries in northern Europe. Nitrate and nitrite from drinking water were not included in the study. Mean daily dietary intake of nitrate was 77 mg, of nitrite 5.3 mg, and of NDMA 0.05 microgram respectively. Intake of NDMA from beer, estimated in a part of the study population, was 0.07 microgram per day. More than 90% of dietary nitrate was derived from vegetables, including potatoes. Nitrite was mainly provided by cured meat products. Cured meat products and smoked and salted fish were important food sources of NDMA. The total daily intake of nitrate was similar in men and women, whereas intakes of nitrite and NDMA were higher in men than in women. The diet of farmers was characterized by lower amounts of nitrate, nitrite and NDMA, whereas white collar workers and those employed in industry had higher intakes. Current smokers were exposed to higher dietary intakes of nitrate, nitrite and NDMA than non-smokers. Intakes of dietary nitrate, nitrite and NDMA estimated on an individual level are suggested to be useful in evaluating the health effects of these compounds in epidemiological studies.

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TL;DR: In this article, the authors found that adding nitrate (as nitrogen) at a concentration of 0.71 mM to a crushed Berea sandstone column with oil field-produced water consortia incubated at 60°C was inhibited by the addition of nitrate.
Abstract: Microbial souring (production of hydrogen sulfide by sulfate-reducing bacteria, SRB) in crushed Berea sandstone columns with oil field-produced water consortia incubated at 60°C was inhibited by the addition of nitrate (NO3) or nitrite (NO 2 − ). Added nitrate (as nitrogen) at a concentration of 0.71 mM resulted in the production of 0.57–0.71 mM nitrite by the native microbial population present during souring and suppressed sulfate reduction to below detection limits. Nitrate added at 0.36 mM did not inhibit active souring but was enough to maintain inhibition if the column had been previously treated with 0.71 mM or greater. Continuous addition of 0.71–0.86 mM nitrite also completely inhibited souring in the column. Pulses of nitrite were more effective than the same amount of nitrite added continuously. Nitrite was more effective at inhibiting souring than was glutaraldehyde, and SRB recovery was delayed longer with nitrite than with glutaraldehyde. It was hypothesized that glutaraldehyde killed SRB while nitrite provided a long-term inhibition without cell death. Removal of nitrate after as long as 3 months of continuous addition allowed SRB in a biofilm to return to their previous level of activity. Inhibition was achieved with much lower levels of nitrate and nitrite, and at higher temperatures, than noted by other researchers.

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TL;DR: In this article, a series of novel complexes containing the CuI−NO2- unit, including monocopper(I), dicoppers(I,I), and mixed valence dicopper( I,II) and copper(I)−zinc(II) species, were prepared, fully characterized, and subjected to reactivity studies designed to probe their ability to produce nitric oxide.
Abstract: In an effort to provide precedence for postulated intermediates in copper-protein-mediated nitrite reduction, a series of novel complexes containing the CuI−NO2- unit, including monocopper(I), dicopper(I,I), and mixed valence dicopper(I,II) and copper(I)−zinc(II) species, were prepared, fully characterized, and subjected to reactivity studies designed to probe their ability to produce nitric oxide. Treatment of solutions of [LCu(CH3CN)]PF6 (L = Li-Pr3, 1,4,7-triisopropyl-1,4,7-triazacyclononane, or LBn3, 1,4,7-tribenzyl-1,4,7-triazacyclononane) in MeOH with excess NaNO2 yielded the novel dicopper(I,I) complexes [(LCu)2(μ-NO2)]PF6. The complex with L = Li-Pr3 was cleaved by PPh3 to afford [Li-Pr3Cu(PPh3)]PF6 and Li-Pr3Cu(NO2), a structural model for the substrate adduct of copper nitrite reductase. Oxidation of the dicopper(I,I) compound (L = Li-Pr3) with (Cp2Fe)(PF6) in CH2Cl2 yielded the deep red, mixed valent, dicopper(I,II) species [(Li-Pr3Cu)2(μ-NO2)](PF6)2, which was structurally characterized as its...

Journal ArticleDOI
TL;DR: Kinetic modeling of these processes has been performed for a widely used experimental system and it appears that measurements of nitrite/nitrate or citrulline accumulation in the bulk cell medium culture during a given time period significantly underestimate the true rate of NO synthesis at the level of the producer cell.
Abstract: Inducible nitric oxide (NO) synthase produces a long-lasting NO flux which can exert cytotoxic effects on target cells. A prerequisite for the understanding of the molecular basis of NO action is quantitative data on the availability of this small neutral radical molecule at both the spatial and temporal levels. The limits of NO availability depend on the respective rates of NO production, diffusion and autoxidation by molecular oxygen. Kinetic modeling of these processes has been performed for a widely used experimental system consisting of a monolayer of adherent cells cultured in vitro for hours in unstirred culture medium. It appears that: (i) the maximal NO concentration in the culture is in the immediate vicinity of the monolayer, where target cells will sediment; (ii) the steady-state NO concentration in this area is lower than 4 to 5 microM; and (iii) measurements of nitrite/nitrate or citrulline accumulation in the bulk cell medium culture during a given time period significantly underestimate (by a factor of up to 3 to 4) the true rate of NO synthesis at the level of the producer cell. This rate can be, nevertheless, easily estimated from the rate of production of the stable NO synthase products.

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TL;DR: Highly sensitive nitrite sensors have been developed for the first time based on mediator-modified electrodes based on redox-active compounds and the detection limit of the enzymatic nitrite sensor was found to be 1 μM nitrite.
Abstract: Highly sensitive nitrite sensors have been developed for the first time based on mediator-modified electrodes. Tetraheme cytochrome c nitrite reductase from Sulfurospirillum deleyianum and cytochrome cd(1) nitrite reductase from Paracoccus denitrificans are able to accept electrons from artificial electron donors, which simultaneously act as electron mediators between the enzyme and an amperometric electrode. In addition to methyl viologen, redox-active compounds such as phenazines (phenosafranin, safranin T, N-methylphenazinium, 1-methoxy-N-methylphenazinium) and triarylmethane redox dyes (bromphenol blue and red) were selected from a range of redox compounds exhibiting the most efficient performance for nitrite detection. After precipitation, the electron mediators were incorporated in a graphite electrode material. Enzyme immobilization is performed by entrapment in a poly(carbamoyl sulfonate) (PCS) hydrogel. Diffusion coefficients and apparent heterogeneous rate constants of the mediators as well as homogeneous rate constants of nitrite sensors were determined by chronoamperometry and cyclic voltammetry. The phenosafranin-modified electrode layered with the PCS hydrogel immobilization of tetraheme cytochrome c nitrite reductase yielded linear current responses up to 250 μM nitrite with a sensitivity of 446.5 mA M(-)(1) cm(-)(2). The detection limit of the enzymatic nitrite sensor was found to be 1 μM nitrite.