Showing papers on "Nitrite published in 1994"

Toxicity of nitrogenous wastes to aquaculture animals

Abstract: The economics of most modern aquaculture operations require that animals be cultured at high densities. A consequence of high‐density aquaculture is the increased probability that the animals will be exposed to elevated concentrations of nitrogenous wastes, particularly ammonia and nitrite. Ammonia toxicity is dependent primarily on the concentration of ammonia and the pH of the environment High concentrations of ammonia will decrease survival, inhibit growth, and cause a variety of physiological dysfunctions. Nitrite toxicity is dependent on the concentration of nitrite and, in many species, the concentration of chloride in the water. Nitrite toxicosis is characterized by reduced survival and growth, methemoglobinemia, and other physiological dysfunctions. Both ammonia and nitrite act as stressors in that they stimulate the release of corticosteroid hormones into circulation. Elevated concentrations of circulating corticosteroids have been linked to impaired immune function and, consequently, de...

Kinetics of the reaction of nitric oxide with oxygen in aqueous solutions.

Abstract: An understanding of the rate of reaction of nitric oxide (NO) with oxygen in aqueous solutions is needed in assessing the various actions of NO in the body. A novel approach was developed for studying the kinetics of this reaction, which permitted simultaneous and continuous measurements of the concentrations of NO and the principal product, nitrite (NO2-). Nitric oxide was measured using a chemiluminescence detector, with continuous sampling achieved by diffusion of NO through a membrane fitted into the base of a small, stirred reactor. The results with various initial NO and O2 concentrations confirmed that the rate of reaction is second-order in NO and first-order in O2. The rate of reaction of NO was described by the expression 4k1 [NO]2[O2], where k1 was (2.1 +/- 0.4) x 10(6) M-2 s-1 at 23 degrees C and (2.4 +/- 0.3) x 10(6) M-2 s-1 at 37 degrees C. The value of k1 was the same at pH 4.9 and 7.4. The rate of formation of NO2- equaled the rate of reaction of NO (within experimental uncertainty of a few percent), and there was no detectable formation of nitrate (NO3-). This confirmed that NO and NO2- were the only NOx species present in significant amounts and supported the validity of pseudo-steady-state assumptions for NO2 and N2O3, which are intermediates in the conversion of NO to NO2-.(ABSTRACT TRUNCATED AT 250 WORDS)

Formation of free nitric oxide from l-arginine by nitric oxide synthase: direct enhancement of generation by superoxide dismutase.

Abstract: Although nitric oxide (NO) appears to be one of the oxidation products of L-arginine catalyzed by NO synthase (NOS; EC 1.14.13.39), past studies on the measurement of NO in cell-free enzymatic assays have not been based on the direct detection of the free NO molecule. Instead, assays have relied on indirect measurements of the stable NO oxidation products nitrite and nitrate and on indirect actions of NO such as guanylate cyclase activation and oxyhemoglobin oxidation. Utilizing a specific chemiluminescence assay, we report here that the gaseous product of L-arginine oxidation, catalyzed by both inducible macrophage and constitutive neuronal NOS, is indistinguishable from authentic NO on the basis of their physicochemical properties. NO gas formation by NOS was dependent on L-arginine, NADPH, and oxygen and inhibited by NG-methyl-L-arginine and cyanide anion. Superoxide dismutase (SOD) caused a marked, concentration-dependent increase in the production of free NO by mechanisms that were unrelated to the dismutation of superoxide anion or activation of NOS. These observations indicate that free NO is formed as a result of NOS-catalyzed L-arginine oxidation and that SOD enhances the generation of NO without directly affecting NO itself. SOD appears to elicit a novel biological action, perhaps accelerating the conversion of an intermediate in the L-arginine-NO pathway such as nitroxyl (HNO) to NO.

Posttranslational Regulation of Nitrate Reductase in Higher Plants.

Abstract: In many plants, nitrogen represents 2 to 6% of dry matter, most of it being present in the form of amino acids, proteins, or nucleic acids. In these organic compounds, nitrogen exists in its most reduced state (oxidation state -3). It is taken up from the soil primarily in the form of nitrate (oxidation state +5). Thus, nitrate has to be reduced by plants at the expense of reductants such as NADH or NADPH, requiring 8 mol of electrons [or 4 mol of NAD(P)H] per mol of nitrate. Reduction is a two-step mechanism. The first step, reduction of nitrate to nitrite (+3 oxidation state), is catalyzed by assimilatory NR, which is an NAD(P)H-dependent cytosolic enzyme. Nitrite is further reduced to ammonia (-3 oxidation state) in the plastids of leaves or roots by NiR. There are at least two important reasons why plants must exert control on the velocity of nitrate reduction. First, it is an energy-consuming process. As shown above, 8 electrons are required to reduce one nitrate to ammonium, but only 4 electrons are needed to reduce CO2 to the carbohydrate level. Accordingly, a C/N ratio of 10 in the plant biomass (a value found in many herbaceous plants) indicates that about 20% of the photosynthetically produced electrons are consumed for nitrate reduction. Plants have to avoid 'luxury' consumption of nitrate and energy. Second, and perhaps more important, the primary product of nitrate reduction, nitrite (NO2-), is cytotoxic and regarded to be mutagenic as a result of the ability to diazotize amino groups. HNO2 is also a weak acid that, in its undissociated form, can easily penetrate biomembranes, thereby leading to acidification of cells or subcellular compartments. Thus, it makes sense if nitrate reduction is controlled in such a way that it does not exceed nitrite and ammonium consumption. In fact, even under rapidly fluctuating environmental conditions, nitrite levels in plant tissues remain low (below 0.1 mM). Apparently, the overall rates of nitrate and nitrite reduction always match the availability of energy and of carbohydrate, perhaps with the exception of some extreme conditions to be discussed below. Synchronization of nitrate reduction and carbon metabolism may occur at the level of transcription or translation of participating enzymes. The expression of NR genes at the transcription level is highly affected by nitrate, but also by light, plant hormones, and other factors (for review, see Solomonson and Barber, 1990; Lillo, 1994). The enzyme protein is rather short-lived, being degraded with a half-time of a few hours (Li and Oaks, 1993). This high turnover rate permits control of nitrate reduction, e.g. in response to nitrate availability (Li and Oaks, 1993). However, over the years, a number of situations have been described in which the level of extractable NRA did not match NR protein or the rate of nitrate reduction in vivo, indicating that yet other regulatory mechanisms might exist that modulate the catalytic activity of the protein (Lillo, 1994, and refs. cited therein). Such a newly discovered type of NR modulation, a reversible protein phosphorylation, will be described below.

Mass Spectrometric Studies of the Effect of pH on the Accumulation of Intermediates in Denitrification by Paracoccus denitrificans

Abstract: We have used a quadrupole mass spectrometer with a gas-permeable membrane inlet for continuous measurements of the production of N2O and N2 from nitrate or nitrite by cell suspensions of Paracoccus denitrificans. The use of nitrate and nitrite labeled with 15N was shown to simplify the interpretation of the results when these gases were measured. This approach was used to study the effect of pH on the production of denitrification intermediates from nitrate and nitrite under anoxic conditions. The kinetic patterns observed were quite different at acidic and alkaline pH values. At pH 5.5, first nitrate was converted to nitrite, then nitrite was converted to N2O, and finally N2O was converted to N2. At pH 8.5, nitrate was converted directly to N2, and the intermediates accumulated to only low steady-state concentrations. The sequential usage of nitrate, nitrite, and nitrous oxide observed at pH 5.5 was simulated by using a kinetic model of a branched electron transport chain in which alternative terminal reductases compete for a common reductant.

Ammonium and nitrite inhibition of methane oxidation by Methylobacter albus BG8 and Methylosinus trichosporium OB3b at low methane concentrations

Abstract: Methane oxidation by pure cultures of the methanotrophs Methylobacter albus BG8 and Methylosinus trichosporium OB3b was inhibited by ammonium choride and sodium nitrite relative to that in cultures assayed in either nitrate-containing or nitrate-free medium. M. albus was generally more sensitive to ammonium and nitrite than M. trichosporium. Both species produced nitrite from ammonium; the concentrations of nitrite produced increased with increasing methane concentrations in the culture headspaces. Inhibition of methane oxidation by nitrite was inversely proportional to headspace methane concentrations, with only minimal effects observed at concentrations of>500 ppm in the presence of 250 μM nitrite. Inhibition increased with increasing ammonium at methane concentrations of 100 ppm. In the presence of 500 μM ammonium, inhibition increased initially with increasing methane concentrations from 1.7 to 100 ppm; the extent of inhibition decreased with methane concentrations of > 100 ppm. The results of this study provide new insights that explain some of the previously observed interactions among ammonium, nitrite, methane, and methane oxidation in soils and aquatic systems.

Inhibition of nitric oxide synthesis is detrimental during endotoxemia.

Abstract: Background: Increased production of nitric oxide has been implicated as a mediator during septic shock and sepsis syndrome. Inhibition of nitric oxide production could be beneficial during endotoxemia to improve the individual's hemodynamic status and possibly outcome. Objective: To evaluate the effects of nitric oxide inhibition on macrophage function and survival in a murine sepsis model. Design: Sixty-eight female Swiss-Webster (ND4) mice were injected with a sublethal dose of Escherichia coli lipopolysaccharide (25 mg/kg). Intervention: The treated group (n=34) received 10 mg/kg of N G -nitro-l-arginine methyl ester at the time of lipopolysaccharide injection. Main Outcome Measures: Blood samples and peritoneal macrophages were obtained at baseline and at 2, 4, and 8 hours after injection. Nitrite levels were measured in 36 mice from plasma and supernatant samples of cultured peritoneal macrophages stimulated with interferon gamma (100 μg/mL) for 48 hours. Thirty-two animals were observed for survival. Results: Administration of N -nitro-l-arginine methyl ester after lipopolysaccharide injection caused significant reductions in macrophage mean nitrite production from 13 and 15 μmol/L to 7 and 11 μmol/L ( P P N -nitro-l-arginine methyl ester after septic challenge compared with 87.5% in controls ( P Conclusion: Inhibition of nitric oxide production is detrimental in this murine model of endotoxemia. (Arch Surg. 1994;129:142-148)

Nitric oxide reductase from Pseudomonas stutzeri. Primary structure and gene organization of a novel bacterial cytochrome bc complex.

Abstract: The oxidation-reduction and spectroscopic properties of various forms of nitrous oxide reductase from Pseudomonas stutzeri were investigated. The high-activity form I of the enzyme (purple, 8 Cu, Mr 140 000) was reduced by a large variety of cationic, anionic and photochemically generated agents. The blue form III was the only product found in these experiments under anaerobic conditions. Reductive (dithionite) and oxidative (ferricyanide) titrations showed that the conversion of the purple form I to the blue species III was fully reversible in the absence of dioxygen. Two kinetically different phases of the reaction of form I with a stoichiometric amount of dithionite (1e−-equivalent/Cu) were detected: in the fast phase (seconds), the purple chromophore with λ-max at 540 nm disappeared almost completely, whereas in the slower phase (minutes) the blue species with λmax around 650 nm was generated. Irrespective of the nature of the reductant the blue species did not react even at large excess of reductant. It was reoxidized by ferricyanide, hydrogen peroxide and nitric oxide. A new, catalytically inactive derivative of nitrous oxide reductase (form V, 2 Cu, Mr 140 000) was isolated from a transposon Tn5-induced mutant with defective chromophore biosynthesis. The pink color of the mutant protein faded almost completely after addition of 0.5e−-equivalent/Cu. In this case no blue species was found, similar to earlier observations for the regenerated, catalytically inactive protein. Varying with the sample and the pH, 50–80% of the total copper of form I was in an electron-paramagnetic-resonance-(EPR)-silent state as compared to 47% in the mutant protein. The broad, featureless EPR signal recorded at 9.32 GHz for the blue, reduced form III of nitrous oxide reductase represented approximately 20% of the total copper. For the blue species no resolution enhancement was achieved at 34 GHz. At this frequency both forms I and V showed similar EPR signals with apparent g-values at 2.16 and 1.99. At 9.32 GHz, form V had an EPR signal with gII at 2.18, AII= 3.55 mT (4 or 5 lines, in contrast to form I) and gI at 2.03. Above 100 K the splitting of the gII region into seven equidistant lines in the EPR signal of the high-activity form I and the hyperfine structure of the perpendicular transition disappeared. Carbon monoxide and nitric oxide, but not nitrous oxide, had marked effects on the spectroscopic properties of the purple form I. Marked effects were also obtained for the exogenous ligands nitrite, azide, cyanate and thiocyanate. The purple chromophore disappeared in the presence of these agents and the gII region of the corresponding EPR spectra at 9.32 GHz broadened. No superhyperfine structure originating from the interaction between the Cu(II) centers of nitrous oxide reductase and these ligands was detected. Nitric oxide also reacted with the reduced form III of the enzyme, giving a species with the spectroscopic properties of the pink form II. A considerable amount of nitrite was generated in the reaction of nitric oxide and the purple form I, depending on the partial pressure and the reaction time. When form I was mixed with hydrogen peroxide or potassium superoxide at 0°C, a blue intermediate with a broad shoulder around 640 nm was observed. The EPR spectrum of the reaction product showed the presence of type 2 Cu(II) centers with gII= 2.26, AII= 18.5 mT and gI= 2.06. The present results indicate that the coordination sphere of the purple Cu centers in nitrous oxide reductase are rather labile towards subtle changes in the environment such as pH and exogenous ligands. The spectroscopic properties of the blue species and its persistence in the presence of strong reductants point towards a catalytic site with Cu in a ‘reduced' state, stabilized by thiol or disulfide sulfur with substantial spin density delocalized onto sulfur.

Intermediacy of organic nitro and nitrite surface species in selective reduction of nitrogen monoxide by propene in the presence of excess oxygen over silica-supported platinum

Abstract: The role of surface species in the selective reduction of nitrogen oxides by propene in the presence of excess oxygen over Pt/SiO 2 has been studied at 393 K mainly with IR spectroscopy. Organic nitro, nitrite and carbonyl species were detected during the reaction. The reactions of those three species with nitrogen dioxide and oxygen took place rapidly, producing N 2 , N 2 O and CO 2 , while the reactivities of those species with nitric oxide and propene were low. Hence, a mechanism is proposed, in which the nitro, nitrite and carbonyl surface species are key reaction intermediates. Similarity in the products between the selective reduction and the oxidation of nitro (nitromethane) or nitrite (n-butylnitrite) compound supported the proposed reaction scheme.

Steroid sex hormones and macrophage function: modulation of reactive oxygen intermediates and nitrite release.

Abstract: PROBLEM In general, females have a more active immune response than do males. The effects of female sex hormones on lymphocytes have been studied extensively but their effects on macrophages are poorly understood. METHOD In this study, peritoneal macrophages (M phi) obtained from male rats were treated in vitro with estradiol (E2), progesterone (P), testosterone (TS), or hydrocortisone (HC) and their effects on superoxide, hydrogen peroxide, and nitrite release determined. RESULTS At concentrations between 10(-10) and 10(-9) M, female and male sex hormones had no significant effect on superoxide release but, at concentrations above or below that range, these hormones stimulated the release of these reactive oxygen intermediates (ROI). In contrast, M phi treated with HC generally exhibited either unaltered or reduced ROI release. CONCLUSIONS These findings suggest that female sex hormones regulate ROI release by M phi in a manner not entirely shared by other steroid hormones. At most concentrations used, E2, P, TS, and HC significantly inhibited nitrite release by M phi. However, with 10(-10) M of E2 or 10(-9)M of P, nitrite release by M phi was not affected. In the presence of anti-TNF antibody, the amounts of superoxide and hydrogen peroxide release were moderately reduced but nitrite release was dramatically inhibited. The sensitivity of M phi to variations in the concentrations of female sex hormones may contribute to gender-related differences in the immune response.

Nitrate and nitrite in foods and the diet

Abstract: Concentrations of nitrate and nitrite have been determined in a range of foods and the dietary intake estimated from the MAFF Total Diet Study. The estimated dietary intake of nitrate ion for the UK population was 54 mg/day and the estimated dietary intake of nitrite ion was in the range 2.4-4.2 mg/day in 1985. The main source of nitrate in the diet is from the consumption of vegetables.

Dynamics of reduction enzymes involved in the denitrification process in pasture soil

Abstract: When oxygen is depleted in soil, reduction enzymes involved in the denitrification process are activated and de novo synthesis of enzymes starts within a few hours. The dynamics of these enzymes and the effect on the concentration of inorganic N formed were investigated for a soil from permanent pasture. Soil was incubated aerobically for 5 days and then amended with 100 mg NO3−-N kg−1. Treatments were with or without C2H2 and with or without chloramphenicol (found to inhibit de novo synthesis of reduction enzymes), purged of all O2, shaken and anaerobically incubated for 48 h while CO2 and N2O production and no3− and NO2− concentrations were monitored. Chloramphenicol was found to have no inhibitory effects on nitrate reduction indicating that nitrate reductase activity persisted in the absence of de novo synthesis. The persistence of nitrite reductase and nitrous oxide reductase was lower as the application of chloramphenicol increased NO2− concentrations and reduced N2 production. In the absence of chloramphenicol, de novo synthesis of nitrite reductase started 5 h and that of nitrous oxide 16 h after anaerobiosis was imposed. It is concluded that the dynamics of nitrite reductase have only a small effect on the N2O production as NO2− concentrations remained below l mg N kg−1 but the low persistence of N2O reductase in combination with its retarded de-repression results in a high N2O-to-N2 ratio when anaerobic conditions are rapidly induced.

Nark is a nitrite-extrusion system involved in anaerobic nitrate respiration by escherichia-coli

Abstract: Escherichia coli can use nitrate as a terminal electron acceptor for anaerobic respiration. A polytopic membrane protein, termed NarK, has been implicated in nitrate uptake and nitrite excretion and is thought to function as a nitrate/nitrite antiporter. The longest-lived radioactive isotope of nitrogen, 13N-nitrate (half-life = 9.96 min) and the nitrite-sensitive fluorophore N-(ethoxycarbonylmethyl)-6-methoxyquinolinium bromide have now been used to define the function of NarK. At low concentrations of nitrate, NarK mediates the electrogenic excretion of nitrite rather than nitrate/nitrite exchange. This process prevents intracellular accumulation of toxic levels of nitrite and allows further detoxification in the periplasm through the action of nitrite reductase.

Elevation of Plasma Nitric Oxide End Products during Focal Cerebral Ischemia and Reperfusion in the Rat

Abstract: We investigated the alterations in the stable end products of nitric oxide, i.e., nitrate and nitrite, in the plasma during and after rat focal cerebral ischemia by an automated procedure based on the Griess reaction. At 2 h of middle cerebral artery (MCA) occlusion, plasma nitrate/nitrite levels were significantly higher (53 ± 8 μM, mean ± SD, n = 5, p < 0.05) than in rats with sham operation (36 ± 9 μM, n = 5), and were mildly elevated at 4 h of MCA occlusion (42 ± 9 μM, n = 5, n.s.). At 30 min of reperfusion after 2 h of MCA occlusion, plasma nitrate/nitrite levels were more markedly elevated (72 ± 7 μM, n = 5, p < 0.01 vs. sham operation), but were moderately elevated at 2 h of reperfusion after 2 h of MCA occlusion (61 ± 10 μM, n = 5, p < 0.05). Plasma nitrite levels were not changed during these experimental periods. Administration of 20 mg/kg of NG-nitro-l-arginine methyl ester (l-NAME) significantly decreased plasma nitrate/nitrite as well as nitrite at 30 min of reperfusion after 2 h of MCA occlu...

Competition between electron acceptors in photosynthesis: Regulation of the malate valve during CO2 fixation and nitrite reduction.

Abstract: For maximal rates of CO2 assimilation in isolated intact spinach chloroplasts the generation of the adequate NADPH/ATP ratio is achieved either by cyclic electron flow around photosystem I or by linear electron transport to oxaloacetate, nitrite or oxygen (Mehler-reaction). The interrelationships between these poising mechanisms turn out to be strictly hierarchical. In the presence of antimycin A, an inhibitor of ferredoxin-dependent cyclic electron transport, the reduction of both, oxaloacetate and nitrite, but not that of oxygen restores CO2 fixation. When oxaloacetate and nitrite are added at low concentrations simultaneously during steady-state CO2 fixation, the reduction of nitrite is clearly preferred over the reduction of oxaloacetate, but CO2 fixation is not influenced. Nitrite reduction is not decreased upon addition of oxaloacetate, but vice versa. This is due to the regulation of NADP-malate dehydrogenase activation by electron pressure via the ferredoxin/thioredoxin system on the one hand, and by the NADPH/(NADP+NADPH) ratio (anabolic reduction charge, ARC) on the other hand. Thus the closing of the ‘malate valve’ prevents drainage of reducing equivalents from the chloroplast (1) when a low ARC indicates a high demand for NADPH in the stroma and (2) when nitrite reduction reduces the electron pressure at ferredoxin. The ‘malate valve’ is opened when cyclic electron transport is inhibited by antimycin A. Under these conditions the rate of malate formation is higher than in the absence of the inhibitor even in the presence of oxaloacetate, thus indicating that the regulation of the ‘malate valve’ functions at various redox states of the acceptor side of Photosystem I.

Interleukin-1 beta stimulates nitrite production in the rat ovary: evidence for heterologous cell-cell interaction and for insulin-mediated regulation of the inducible isoform of nitric oxide synthase.

Abstract: Recent studies suggest that endogenously generated nitric oxide (NO) may mediate the effects of cytokines in a variety of tissues. In an effort to determine whether NO generation mediates any of the intraovarian actions of interleukin-1 beta (IL-1 beta), we have looked for and characterized the accumulation of nitrite by IL-1 beta-treated, cultured whole ovarian dispersates. Application of IL-1 beta significantly enhanced basal nitrite release in a dose-, cell density- and time-dependent manner, the latter characterized by a lag time of about 20 h, suggestive of induction of NO synthase (NOS). Cellular NOS activity was also elevated by IL-1 beta. Sustained nitrite accumulation required continuous application of IL-1 beta. The maximally stimulating dose of IL-1 beta (50 ng/ml) produced a 10-fold increase in nitrite accumulation by 96 h of culture, an effect reduced 23% when cells were cultured in substrate (i.e., arginine)-free media. IL-1 beta-stimulated nitrite accumulation was reduced to control levels by the simultaneous application of an IL-1 beta receptor antagonist, thereby suggesting a specific receptor-mediated effect. Both the control and IL-1 beta-stimulated levels of nitrite accumulation were attenuated in a dose-dependent manner by inhibitors that favor the inducible form of NOS. In contrast, selective inhibitors of the constitutive form of NOS were significantly less potent. No inhibition was noted after application of an inactive stereoisomeric analogue. IL-1 beta-induced nitrite accumulation was shown to require cell-cell interaction between granulosa and theca-interstitial cells.(ABSTRACT TRUNCATED AT 250 WORDS)