Showing papers on "Nitrite published in 2003"

Nitrite reduction to nitric oxide by deoxyhemoglobin vasodilates the human circulation.

Abstract: Nitrite anions comprise the largest vascular storage pool of nitric oxide (NO), provided that physiological mechanisms exist to reduce nitrite to NO. We evaluated the vasodilator properties and mechanisms for bioactivation of nitrite in the human forearm. Nitrite infusions of 36 and 0.36 μmol/min into the forearm brachial artery resulted in supra- and near-physiologic intravascular nitrite concentrations, respectively, and increased forearm blood flow before and during exercise, with or without NO synthase inhibition. Nitrite infusions were associated with rapid formation of erythrocyte iron-nitrosylated hemoglobin and, to a lesser extent, S-nitroso-hemoglobin. NO-modified hemoglobin formation was inversely proportional to oxyhemoglobin saturation. Vasodilation of rat aortic rings and formation of both NO gas and NO-modified hemoglobin resulted from the nitrite reductase activity of deoxyhemoglobin and deoxygenated erythrocytes. This finding links tissue hypoxia, hemoglobin allostery and nitrite bioactivation. These results suggest that nitrite represents a major bioavailable pool of NO, and describe a new physiological function for hemoglobin as a nitrite reductase, potentially contributing to hypoxic vasodilation.

Measurement of Nitric Oxide Production in Biological Systems by Using Griess Reaction Assay

Abstract: A review of using Griess Reaction method to determine nitric oxide production in biological systems.

Nitrite disrupts multiple physiological functions in aquatic animals.

Abstract: Nitrite is a potential problem in aquatic environments. Freshwater fish actively take up nitrite across the gills, leading to high internal concentrations. Seawater fish are less susceptible but do take up nitrite across intestine and gills. Nitrite has multiple physiological effects. Its uptake is at the expense of chloride, leading to chloride depletion. Nitrite also activates efflux of potassium from skeletal muscle and erythrocytes, disturbing intracellular and extracellular K(+) levels. Nitrite transfer across the erythrocytic membrane leads to oxidation of haemoglobin to methaemoglobin (metHb), compromising blood O(2) transport. Other haem proteins are also oxidised. Hyperventilation is observed, and eventually tissue O(2) shortage becomes reflected in elevated lactate concentrations. Heart rate increases rapidly, before any significant elevations in metHb or extracellular potassium occur. This suggests nitrite-induced vasodilation (possibly via nitric oxide generated from nitrite) that is countered by increased cardiac pumping to re-establish blood pressure. Nitrite can form and/or mimic nitric oxide and thereby interfere with processes regulated by this local hormone. Steroid hormone synthesis may be inhibited, while changes in ammonia and urea levels and excretion rates reflect an influence of nitrite on nitrogen metabolism. Detoxification of nitrite occurs via endogenous oxidation to nitrate, and elimination of nitrite takes place both via gills and urine. The susceptibility to nitrite varies between species and in some cases also within species. Rainbow trout fall into two groups with regard to susceptibility and physiological response. These two groups are not related to sex but show significant different nitrite uptake rates.

Metabolism of Inorganic N Compounds by Ammonia-Oxidizing Bacteria

Abstract: Ammonia oxidizing bacteria extract energy for growth from the oxidation of ammonia to nitrite. Ammonia monooxygenase, which initiates ammonia oxidation, remains enigmatic given the lack of purified preparations. Genetic and biochemical studies support a model for the enzyme consisting of three subunits and metal centers of copper and iron. Knowledge of hydroxylamine oxidoreductase, which oxidizes hydroxylamine formed by ammonia monooxygenase to nitrite, is informed by a crystal structure and detailed spectroscopic and catalytic studies. Other inorganic nitrogen compounds, including NO, N2O, NO2, and N2 can be consumed and/or produced by ammonia-oxidizing bacteria. NO and N2O can be produced as byproducts of hydroxylamine oxidation or through nitrite reduction. NO2 can serve as an alternative oxidant in place of O2 in some ammonia-oxidizing strains. Our knowledge of the diversity of inorganic N metabolism by ammonia-oxidizing bacteria continues to grow. Nonetheless, many questions remain regarding the enzymes and genes involved in these processes and the role of these pathways in ammonia oxidizers.

A mechanism of abiotic immobilization of nitrate in forest ecosystems: the ferrous wheel hypothesis

Abstract: Forest soils, rather than woody biomass, are the dominant long-term sink for N in forest fertilization studies and, by inference, for N from atmospheric deposition. Recent evidence of significant abiotic immobilization of inorganic-N in forest humus layers challenges a previously widely held view that microbial processes are the dominant pathways for N immobilization in soil. Understanding the plant, microbial, and abiotic mechanisms of N immobilization in forest soils has important implications for understanding current and future carbon budgets. Abiotic immobilization of nitrate is particularly perplexing because the thermodynamics of nitrate reduction in soils are not generally favorable under oxic conditions. Here we present preliminary evidence for a testable hypothesis that explains abiotic immobilization of nitrate in forest soils. Because iron (and perhaps manganese) plays a key role as a catalyst, with Fe(II) reducing nitrate and reduced forms of carbon then regenerating Fe(II), we call this ‘the ferrous wheel hypothesis’. After nitrate is reduced to nitrite, we hypothesize that nitrite reacts with dissolved organic matter through nitration and nitrosation of aromatic ring structures, thus producing dissolved organic nitrogen (DON). In addition to ignorance about mechanisms of DON production, little is known about DON dynamics in soil and its fate within ecosystems. Evidence from leaching and watershed studies suggests that DON production and consumption may be largely uncoupled from seasonal biological processes, although biological processes ultimately produce the DOC and reducing power that affect DON formation and the entire N cycle. The ferrous wheel hypothesis includes both biological and abiological processes, but the reducing power of plant-derived organic matter may build up over seasons and years while the abiotic reduction of nitrate and reaction of organic matter with nitrite may occur in a matter of seconds after nitrate enters the soil solution.

Health Implications of Exposure to Environmental Nitrogenous Compounds

Abstract: All living systems need nitrogen for the production of complex organic molecules, such as proteins, nucleic acids, vitamins, hormones and enzymes. Due to the intense use of synthetic nitrogen fertilisers and livestock manure in modern day agriculture, food (particularly vegetables) and drinking water may contain higher concentrations of nitrate than in the past. The mean intake of nitrate per person in Europe is about 50–140 mg/ day and in the US about 40–100 mg/day. In the proximal small intestine, nitrate is rapidly and almost completely absorbed (bioavailability at least 92%). In humans, approximately, 25% of the nitrate ingested is secreted in saliva, where some 20% (about 5–8% of the nitrate intake) is converted to nitrite by commensal bacteria. The nitrite so formed is then absorbed primarily in the small intestine. Nitrate may also be synthesised endogenously from nitric oxide (especially in case of inflammation), which reacts to form nitrite. Normal healthy adults excrete in the urine approximately 62mg nitrate ion/day from endogenous synthesis. Thus, when nitrate intake is low and there are no additional exogenous sources (e.g. gastrointestinal infections), the endogenous production of nitrate is more important than exogenous sources. Nitrate itself is generally regarded nontoxic. Toxicity is usually the result of the conversion of nitrate into the more toxic nitrite. There are two major toxicological concerns regarding nitrite. First, nitrite may induce methaemoglobinaemia, which can result in tissue hypoxia, and possibly death. Secondly, nitrite may interact with secondary or N-alkyl-amides to form N-nitroso carcinogens. However, epidemiological investigations and human toxicological studies have not shown an unequivocal relationship between nitrate intake and the risk of cancer. The Joint Expert Committee of the Food and Agriculture Organization of the United Nations/World Health Organization (JECFA) and the European Commission’s Scientific Committee on Food have set an acceptable daily intake (ADI) for nitrate of 0–3.7mg nitrate ion/kg bodyweight; this appears to be safe for healthy neonates, children and adults. The same is also true of the US Environmental Protection Agency (EPA) Reference Dose (RfD) for nitrate of 1.6mg nitrate nitrogen/kg bodyweight per day (equivalent to about 7.0mg nitrate ion/kg bodyweight per day). This opinion is supported by a recent human volunteer study in which a single dose of nitrite, equivalent to 15–20 times the ADI for nitrate, led to only mild methaemoglobinaemia (up to 12.2%), without other serious adverse effects. The JECFA has proposed an ADI for nitrite of 0–0.07mg nitrite ion/kg bodyweight and the EPA has set an RfD of 0.1mg nitrite nitrogen/kg bodyweight per day (equivalent to 0.33mg nitrite ion/kg bodyweight per day). These values are again supported by human volunteer studies.

Nitrite reductase activity of sulphate-reducing bacteria prevents their inhibition by nitrate-reducing, sulphide-oxidizing bacteria

Abstract: Sulphate-reducing bacteria (SRB) can be inhibited by nitrate-reducing, sulphide-oxidizing bacteria (NR-SOB), despite the fact that these two groups are interdependent in many anaerobic environments. Practical applications of this inhibition include the reduction of sulphide concentrations in oil fields by nitrate injection. The NR-SOB Thiomicrospira sp. strain CVO was found to oxidize up to 15 mM sulphide, considerably more than three other NR-SOB strains that were tested. Sulphide oxidation increased the environmental redox potential (Eh) from -400 to +100 mV and gave 0.6 nitrite per nitrate reduced. Within the genus Desulfovibrio, strains Lac3 and Lac6 were inhibited by strain CVO and nitrate for the duration of the experiment, whereas inhibition of strains Lac15 and D. vulgaris Hildenborough was transient. The latter had very high nitrite reductase (Nrf) activity. Southern blotting with D. vulgaris nrf genes as a probe indicated the absence of homologous nrf genes from strains Lac3 and Lac6 and their presence in strain Lac15. With respect to SRB from other genera, inhibition of the known nitrite reducer Desulfobulbus propionicus by strain CVO and nitrate was transient, whereas inhibition of Desulfobacterium autotrophicum and Desulfobacter postgatei was long-lasting. The results indicate that inhibition of SRB by NR-SOB is caused by nitrite production. Nrf-containing SRB can overcome this inhibition by further reducing nitrite to ammonia, preventing a stalling of the favourable metabolic interactions between these two bacterial groups. Nrf, which is widely distributed in SRB, can thus be regarded as a resistance factor that prevents the inhibition of dissimilatory sulphate reduction by nitrite.

Chemical nature of nitric oxide storage forms in rat vascular tissue

Abstract: Endothelial NO production results in local formation of adducts that may act as storage forms of NO. Because little is known about their chemical nature, concentrations, and possible role in vascular biology, we sought to characterize those species basally present in rat aorta, using two independent approaches. In the first approach, tissue homogenates were analyzed by using chemiluminescence- and ion-chromatography-based techniques that allow trace-level quantification of NO-related compounds in complex biological matrices. In the second approach, NO stores were characterized by their ability to release NO when illuminated with light and subsequently relax vascular smooth muscle (photorelaxation). The latter included a careful assessment of action spectra for photorelaxation, taking into account the light-scattering properties of the tissue and the storage depletion rates induced by exposure to controlled levels of light. Biochemical analyses revealed that aortic tissues contained 10 ± 1 μM nitrite, 42 ± 7 μM nitrate, 40 ± 6 nM S-nitroso, and 33 ± 6 nM N-nitroso compounds (n = 4–8). The functional data obtained suggest that the NO photolytically released in the tissue originated from species with photophysical properties similar to those reported for low-molecular-weight S-nitrosothiols, as well as from nitrite. The relative contribution of these potential NO stores to the extent of photorelaxation was consistent with their concentrations detected biochemically in vascular tissue when their photoactivity was taken into account. We conclude that intravascular nitroso species and nitrite both have the potential to release physiologically relevant quantities of NO independent of enzymatic control by NO synthase.

Methodologies for the sensitive and specific measurement of S-nitrosothiols, iron-nitrosyls, and nitrite in biological samples.

Abstract: (2003). Methodologies for the Sensitive and Specific Measurement of S -nitrosothiols, Iron-nitrosyls, and Nitrite in Biological Samples. Free Radical Research: Vol. 37, No. 1, pp. 1-10.

Characterization of the magnitude and kinetics of xanthine oxidase-catalyzed nitrate reduction: evaluation of its role in nitrite and nitric oxide generation in anoxic tissues.

Abstract: In addition to nitric oxide (NO) generation from specific NO synthases, NO is also formed during anoxia from nitrite reduction, and xanthine oxidase (XO) catalyzes this process. While in tissues and blood high nitrate levels are present, questions remain regarding whether nitrate is also a source of NO and if XO-mediated nitrate reduction can be an important source of NO in biological systems. To characterize the kinetics, magnitude, and mechanism of XO-mediated nitrate reduction under anaerobic conditions, EPR, chemiluminescence NO-analyzer, and NO-electrode studies were performed. Typical XO reducing substrates, xanthine, NADH, and 2,3-dihydroxybenz-aldehyde, triggered nitrate reduction to nitrite and NO. The rate of nitrite production followed Michaelis-Menten kinetics, while NO generation rates increased linearly following the accumulation of nitrite, suggesting stepwise-reduction of nitrate to nitrite then to NO. The molybdenum-binding XO inhibitor, oxypurinol, inhibited both nitrite and NO production, indicating that nitrate reduction occurs at the molybdenum site. At higher xanthine concentrations, partial inhibition was seen, suggesting formation of a substrate-bound reduced enzyme complex with xanthine blocking the molybdenum site. The pH dependence of nitrite and NO formation indicate that XO-mediated nitrate reduction occurs via an acid-catalyzed mechanism. With conditions occurring during ischemia, myocardial xanthine oxidoreductase and nitrate levels were determined to generate up to 20 microM nitrite within 10-20 min that can be further reduced to NO with rates comparable to those of maximally activated NOS. Thus, XOR catalyzed nitrate reduction to nitrite and NO occurs and can be an important source of NO production in ischemic tissues.

Enrichment of denitrifying glycogen-accumulating organisms in anaerobic/anoxic activated sludge system.

Abstract: Denitrifying glycogen-accumulating organisms (DGAO) were successfully enriched in a lab-scale sequencing batch reactor (SBR) running with anaerobic/anoxic cycles and acetate feeding during the anaerobic period. Acetate was completely taken up anaerobically, which was accompanied by the consumption of glycogen and the production of poly-beta-hydroxy-alkanoates (PHA). In the subsequent anoxic stage, nitrate or nitrite was utilized as electron acceptor for the oxidation of PHA, resulting in glycogen replenishment and cell growth. The above phenotype showed by the enrichment culture demonstrates the existence of DGAO. Further, it was found that the anaerobic behavior of DGAO could be predicted well by the anaerobic GAO model of Filipe et al. (2001) and Zeng et al. (2002a). The final product of denitrification during anoxic stage was mainly nitrous oxide (N2O) rather than N-2. The data strongly suggests that N2O production may be caused by the inhibition of nitrous oxide reductase by an elevated level of nitrite accumulated during denitrification. The existence of these organisms is a concern in biological nutrient removal systems that typically have an anaerobic/anoxic/aerobic reactor sequence since they are potential competitors to the polyphosphate-accumulating organisms. (C) 2003 Wiley Periodicals, Inc.

Accumulation of nitrogen oxides in copper-limited cultures of denitrifying bacteria

Abstract: Three strains of heterotrophic denitrifying bacteria were cultured in artificial seawater medium under trace metal clean conditions to investigate their physiological response to changes in copper concentration. Decreasing the copper concentration in cultures of Pseudomonas stutzeri and Paracoccus denitrificans resulted in accumulation of nitrous oxide (N 2 O) gas compared to copper-replete cultures and cessation of growth before complete denitrification to dinitrogen. Correspondingly, the activity of the copper enzyme nitrous oxide reductase, measured for P. denitrificans cultures, was high in copper-replete cultures and was below detection in copper-deficient cultures. Addition of copper to copper-deficient cultures following the accumulation of N 2 O resulted in resumption of growth and complete consumption of N 2 O in solution. Growth of the third strain, WLB20, in copper-deficient medium caused a marked accumulation of nitrite, suggesting that WLB20 has the copper form of nitrite reductase. These observations suggest a role for trace metals in regulating redox cycling of nitrogen and trace gas production in the ocean.

Containment of Biogenic Sulfide Production in Continuous Up-Flow Packed-Bed Bioreactors with Nitrate or Nitrite

Abstract: Produced water from the Coleville oil field in Saskatchewan, Canada was used to inoculate continuous up-flow packed-bed bioreactors. When 7.8 mM sulfate and 25 mM lactate were present in the in-flowing medium, H(2)S production (souring) by sulfate-reducing bacteria (SRB) was prevented by addition of 17.5 mM nitrate or 20 mM nitrite. Changing the sulfate or lactate concentration of the in-flowing medium indicated that the concentrations of nitrate or nitrite required for containment of souring decreased proportionally with a lowered concentration of the electron donor lactate, while the sulfate concentration of the medium had no effect. Microbial communities were dominated by SRB. Nitrate addition did not give rise to changes in community composition, indicating that lactate oxidation and H(2)S removal were caused by the combined action of SRB and nitrate-reducing, sulfide-oxidizing bacteria (NR-SOB). Apparently the nitrite concentrations formed by these NR-SOB did not inhibit the SRB sufficiently to cause community shifts. In contrast, significant community shifts were observed upon direct addition of high concentrations (20 mM) of nitrite. Strains NO3A and NO2B, two newly isolated, nitrate-reducing bacteria (NRB) emerged as major community members. These were found to belong to the epsilon-division of the Proteobacteria, to be most closely related to Campylobacter lari, and to oxidize lactate with nitrate or nitrite as the electron acceptor. Thus the mechanism of microbial H(2)S removal in up-flow packed-bed bioreactors depended on whether nitrate (SRB/NR-SOB) or nitrite (SRB/NR-SOB as well as NRB) was used. However, the amount of nitrate or nitrite needed to completely remove H(2)S was dictated by the electron donor (lactate) concentration, irrespective of mechanism.

Isolation and Characterization of a Sulfur-Oxidizing Chemolithotroph Growing on Crude Oil under Anaerobic Conditions

Abstract: Molecular approaches have shown that a group of bacteria (called cluster 1 bacteria) affiliated with the epsilon subclass of the class Proteobacteria constituted major populations in underground crude-oil storage cavities. In order to unveil their physiology and ecological niche, this study isolated bacterial strains (exemplified by strain YK-1) affiliated with the cluster 1 bacteria from an oil storage cavity at Kuji in Iwate, Japan. 16S rRNA gene sequence analysis indicated that its closest relative was Thiomicrospira denitrificans (90% identity). Growth experiments under anaerobic conditions showed that strain YK-1 was a sulfur-oxidizing obligate chemolithotroph utilizing sulfide, elemental sulfur, thiosulfate, and hydrogen as electron donors and nitrate as an electron acceptor. Oxygen also supported its growth only under microaerobic conditions. Strain YK-1 could not grow on nitrite, and nitrite was the final product of nitrate reduction. Neither sugars, organic acids (including acetate), nor hydrocarbons could serve as carbon and energy sources. A typical stoichiometry of its energy metabolism followed an equation: S(2-) + 4NO(3)(-) --> SO(4)(2-) + 4NO(2)(-) (Delta G(0) = -534 kJ mol(-1)). In a difference from other anaerobic sulfur-oxidizing bacteria, this bacterium was sensitive to NaCl; growth in medium containing more than 1% NaCl was negligible. When YK-1 was grown anaerobically in a sulfur-depleted inorganic medium overlaid with crude oil, sulfate was produced, corresponding to its growth. On the contrary, YK-1 could not utilize crude oil as a carbon source. These results suggest that the cluster 1 bacteria yielded energy for growth in oil storage cavities by oxidizing petroleum sulfur compounds. Based on its physiology, ecological interactions with other members of the groundwater community are discussed.

Activity of three disinfectants and acidified nitrite against Clostridium difficile spores.

Abstract: Objective:To identify environmentally safe, rapidly acting agents for killing spores of Clostridium difficile in the hospital environment.Design:Three classic disinfectants (2% glutaraldehyde, 1.6% peracetyl ions, and 70% isopropanol) and acidified nitrite were compared for activity against C. difficile spores. Four strains of C. difficile belonging to different serogroups were tested using a dilution–neutralization method according to preliminary European Standard prEN 14347. For peracetyl ions and acidified nitrite, the subjective cleaning effect and the sporicidal activity was also tested in the presence of organic load.Results:Peracetyl ions were highly sporicidal and yielded a minimum 4 log10 reduction of germinating spores already at short exposure times, independent of organic load conditions. Isopropanol 70% showed low or no inactivation at all exposure times, whereas glutaraldehyde and acidified nitrite each resulted in an increasing inactivation factor (IF) over time, from an IF greater than 1.4 at 5 minutes of exposure time to greater than 4.1 at 30 minutes. Soiling conditions did not influence the effect of acidified nitrite. There was no difference in the IF among the 4 strains tested for any of the investigated agents. Acidified nitrite demonstrated a good subjective cleaning effect and peracetyl ions demonstrated a satisfactory effect.Conclusions:Cidal activity was shown against C. difficile spores by glutaraldehyde, peracetyl ions, and acidified nitrite. As acidified nitrite and peracetyl ions are considered to be environmentally safe chemicals, these agents seem well suited for the disinfection of C. difficile spores in the hospital environment.

New Processes in the Environmental Chemistry of Nitrite. 2. The Role of Hydrogen Peroxide

Abstract: The oxidation of nitrite and nitrous acid to •NO2 upon irradiation of dissolved Fe(III), ferric (hydr)oxides, and nitrate has previously been shown to enhance phenol nitration. This allowed the proposal of a new role for nitrite and nitrous acid in natural waters and atmospheric aerosols. This paper deals with the interaction between hydrogen peroxide, a key environmental factor in atmospheric oxidative chemistry, and nitrite/nitrous acid. The reaction between nitrous acid and hydrogen peroxide yields peroxynitrous acid, a powerful nitrating agent and an important intermediate in atmospheric chemistry. The kinetics of this reaction is compatible with a rate-determining step involving either H3O2+ and HNO2 or H2O2 and protonated nitrous acid. In the former case the rate constant between the two species would be 179.6 ± 1.4 M-1 s-1, in the latter case it would be as high as (1.68 ± 0.01) × 1010 M-1 s-1 (diffusion-controlled reaction). Due to the more reasonable value of the rate constant, the reaction betwe...