Showing papers on "Nitrite published in 1990"

Activated macrophages destroy intracellular Leishmania major amastigotes by an L-arginine-dependent killing mechanism.

Abstract: Macrophages infected with amastigotes of Leishmania major and treated with IFN-gamma in vitro develop potent antimicrobial activities that eliminate the intracellular parasite. This antileishmanial activity was suppressed in a dose dependent fashion by NG-monomethyl-L-arginine (NGMMLA), a competitive inhibitor of nitrite, nitrate, nitric oxide and L-citrulline synthesis from L-arginine. Excess L-arginine added to infected macrophage cultures reversed the inhibitory effects of NGMMLA. Addition of arginase to culture media inhibited intracellular killing by IFN-gamma-treated cells. Similar effects were seen with macrophages obtained from BCG-infected C3H/HeN mice. Increased levels of nitrite, an oxidative product of the L-arginine-dependent effector mechanism, was measured in cultures of infected IFN gamma-treated macrophages as well as infected BCG-activated macrophages. Nitrite production correlated with development of antileishmanial activity. Nitrite production and microbicidal activity both decreased when in vivo or in vitro-activated macrophages were cultured in the presence of either arginase or NGMMLA. Nitric oxide synthesized from a terminal guanidino nitrogen atom of L-arginine and a precursor of the nitrite measured, may disrupt Fe-dependent enzymatic pathways vital to the survival of amastigotes within macrophages.

Nitrates, nitrites and N-nitrosocompounds: a review of the occurrence in food and diet and the toxicological implications.

Abstract: Data on occurrence of nitrate, nitrite and N-nitrosocompounds in food and drinking water, and on total dietary intakes are reviewed. Metabolic, toxicological and epidemiological studies are surveyed and the implications with respect to safety evaluation are addressed. It is concluded that, on the basis of recent long-term animal studies and of clinical experience in man, the current Acceptable Daily Intake (ADI) allocated to nitrate by the Joint FAO/WHO Expert Committee on Food Additives of 0-5 mg/kg body weight/day (expressed as sodium nitrate) might be increased to 0-25 mg/kg body weight/day. Based on similar criteria, the ADI for nitrite would be 0-0.1 mg/kg body weight/day (expressed as sodium nitrite). In view of the known carcinogenicity of N-nitrosocompounds, exposure to these compounds in food should be minimized by appropriate technological means, such as lowering the nitrite concentration in preserved foods to the minimum required to ensure microbiological safety and use of inhibitors of nitrosation like alpha-tocopherol or ascorbic acid. Further work is needed to define the minimal levels of nitrite in foods needed to inhibit outgrowth of Clostridium botulinum and toxin production.

Metabolic fate of L-arginine in relation to microbiostatic capability of murine macrophages.

Abstract: L-arginine is required for the fungistatic action of murine macrophages in vitro. To further investigate this requirement, L-arginine metabolism by macrophages was measured under conditions where fungistasis either succeeded or failed. Macrophage fungistasis correlated with metabolism of L-arginine to citrulline, nitrite, and nitrate. The metabolic rate was dependent on extracellular L-arginine concentration, reaching a maximum of 67 nmol nitrite/h per mg protein. It accounted for one-third of arginine consumed by fungistatic macrophages. Equimolar amounts of citrulline and total nitrite plus nitrate accumulated in medium. This was consistent with the hypothesis that one of the equivalent guanidino nitrogens of L-arginine was oxidized to both nitrite and nitrate leaving L-citrulline as the amino acid reaction product. The analogue, NG-mono-methyl-L-arginine, selectively inhibited nitrogen oxidation and it was shown previously that it inhibited fungistatic capability. Resident macrophages were not fungistatic and their nitrogen oxidation was low. Once macrophages began producing nitrite/nitrate, protein synthesis was not required during the next 8 h for either fungistasis or nitrogen oxidation. Two-thirds of L-arginine consumption was due to macrophage arginase yielding L-ornithine and urea, which accumulated in medium. This activity was dissociated from macrophage fungistasis. Nitrogen oxidation metabolism by macrophages is linked to a mechanism that inhibits proliferation of fungi. This may involve synthesis of an intermediate compound(s) that has antimicrobial properties.

Pigments, size, and distributions of Synechococcus in the North Atlantic and Pacific Oceans

Abstract: Dual-beam flow cytometry was used to analyze the distribution and optical characteristics of Synechococcus in the North Atlantic and Pacific Oceans. The depth range over which Synechococcus cells were abundant was related to the depth of the nitrite maximum and the chlorophyll maximum, but was not significantly correlated with the depth of the surface isothermal layer. Dual-beam analysis of chromophore pigment types revealed that the majority of the populations were of the high-urobilin type; low-urobilin types, similar to the isolate WH7803, were found only in coastal waters where they almost always co-occurred with high-urobilin strains. Phycoerythrin fluorescence intensity per cell increased dramatically with depth in the lower euphotic zone at all stations; at some open-ocean stations, very deep cells were as much as 100 times brighter than those at the surface. The maximal fluorescence intensity per cell was about the same at the coastal and oceanic stations, and the depth of maximal fluorescence was closely related to the depth of the nitrite maximum. At most stations, fluorescence per cell was constant throughout the mixed layer, but at some open-ocean stations it decreased continuously to the surface. The latter pattern suggests that mixing rates in these areas are slow relative to the abilities of the cells to photoacclimate. A distinct diel pattern in forward-angle light scatter was observed in cells in the mixed layer over vast regions, which we hypothesize to be coupled to growth of the cells during daylight hours.

Estimation of rate constants for near-diffusion-controlled reactions in water at high temperatures

Abstract: Rate constants measured over the temperature range 20–200 °C are reported for the following reactions: (a) reaction of the hydrated electron with oxygen, the proton, hydrogen peroxide, nitrate, nitrite, nitrobenzene and methyl viologen; (b) reaction of the hydroxyl radical with another hydroxyl radical and ferrocyanide; (c) reaction of the hydrogen atom with permanganate and oxygen. To evaluate methods of estimating rate constants at high temperatures these rate constants and others in the literature have been fitted to the following equation: kobs=kdiff/(1 +kdiff/kreact), where kobs is the measured rate constant for the bimolecular reaction in solution, kdiff is the encounter rate constant of the two reacting species, and kreact is the rate constant that would be measured if diffusion of the species was not rate influencing. With the exception of reactions of the hydrated electron with nitrate and nitrite ions and nitrous oxide, good fits have been obtained to the above equation, and the results demonstrate that few, if any, of the reactions which are pertinent to water radiolysis are truly diffusion controlled at elevated temperatures.

Bacterial transformations of inorganic nitrogen in the oxygen-deficient waters of the Eastern Tropical South Pacific Ocean

Abstract: Rates of transformations of inorganic nitrogen were measured in the low oxygen, subsurface waters (50–450 m) of the Eastern Tropical South Pacific during February 1985, using 15N tracer techniques. Oxygen concentrations over the entire region were in a range (O2 Measured rates of nitrate reduction and estimated rates of denitrification were sufficient to respire nearly all of the surface primary production that might be transported into the oxygen deficient zone. These results imply that the supply of labile organic material, especially from the surface, was more important than oxygen concentration in modulating the rates of nitrogen transformations within the low oxygen water mass of the Eastern Tropical South Pacific. The pattern of nitrite oxidation and nitrite reduction activities in the oxygen minimum zone supports the hypothesis ( Anderson et al., 1982, Deep-Sea Research, 29, 1113–1140) that nitrite, produced from nitrate reduction, can be recycled by oxidation at the interface between low and high oxygen waters. Rates for denitrification, estimated from nitrate reduction rates, were in harmony with previous estimates based on electron transport system (ETS) measurements and analysis of the nitrate deficit and water residence times. Assimilation rates of NH4+ were substantial, providing evidence for heterotrophic bacterial growth in low oxygen waters. Ambient concentrations of ammonium were maintained at low values primarily by assimilation; ammonium oxidation was an important mechanism at the surface boundary of the low oxygen zone.

Production of nitric oxide in Nitrosomonas europaea by reduction of nitrite

Abstract: Nitrosomonas europaea and Nitrosovibrio sp. produced NO and N2O during nitrification of ammonium. Less then 15% of the produced NO was due to chemical decomposition of nitrite. Production of NO and especially of N2O increased when the bacteria were incubated under anaerobic conditions at decreasing flow rates of air, or at increasing cell densities. Low concentrations of chlorite (10 μM) inhibited the production of NO and N2, but not of nitrite indicating that NO and N2O were not produced during the oxidative conversion of ammonium to nitrite. NO and N2O were produced during reduction of nitrite with hydrazine as electron donor in almost stoichiometric quantities indicating that reduction of nitrite was the main source of NO and N2O.

Contributions of autotrophic and heterotrophic nitrifiers to soil NO and N2O emissions

Abstract: Soil emission of gaseous N oxides during nitrification of ammonium represents loss of an available plant nutrient and has an important impact on the chemistry of the atmosphere. We used selective inhibitors and a glucose amendment in a factorial design to determine the relative contributions of autotrophic ammonium oxidizers, autotrophic nitrite oxidizers, and heterotrophic nitrifiers to nitric oxide (NO) and nitrous oxide (N2O) emissions from aerobically incubated soil following the addition of 160 mg of N as ammonium sulfate kg−1. Without added C, peak NO emissions of 4 μg of N kg−1 h−1 were increased to 15 μg of N kg−1 h−1 by the addition of sodium chlorate, a nitrite oxidation inhibitor, but were reduced to 0.01 μg of N kg−1 h−1 in the presence of nitrapyrin [2-chloro-6-(trichloromethyl)-pyridine], an inhibitor of autotrophic ammonium oxidation. Carbon-amended soils had somewhat higher NO emission rates from these three treatments (6, 18, and 0.1 μg of N kg−1 h−1 after treatment with glucose, sodium chlorate, or nitrapyrin, respectively) until the glucose was exhausted but lower rates during the remainder of the incubation. Nitrous oxide emission levels exhibited trends similar to those observed for NO but were about 20 times lower. Periodic soil chemical analyses showed no increase in the nitrate concentration of soil treated with sodium chlorate until after the period of peak NO and N2O emissions; the nitrate concentration of soil treated with nitrapyrin remained unchanged throughout the incubation. These results suggest that chemoautotrophic ammonium-oxidizing bacteria are the predominant source of NO and N2O produced during nitrification in soil.

Different physiological roles of two independent pathways for nitrite reduction to ammonia by enteric bacteria.

Abstract: Operon fusion strains and mutants of Escherichia coli K-12 lacking the NADH-dependent nitrite reductase have been used to determine the regulation and physiological roles of two independent pathways for nitrite reduction to ammonia. Both the formate- and NADH-dependent pathways (Nrf and Nir, respectively) were totally repressed during aerobic growth, partially active during anaerobic growth in the absence of nitrite and further induced anaerobically by nitrite. Both were dependent upon a functional Fnr protein (a transcription activator of genes for anaerobic respiration). During anaerobic growth in the presence of nitrate, the Nir pathway was fully induced but Nrf was strongly repressed. Mutants defective in the NarL protein, which induces transcription of nitrate reductase genes but represses fumarate reductase genes in the presence of nitrate, were derepressed for Nrf activity during growth with nitrate, but the Nir enzyme was less active. The synthesis of Nrf components was also sensitive to glucose repression and weak activation by NarL during growth in the absence of nitrate. These data indicate that the Nir pathway provides a mechanism for detoxifying nitrite formed in the cytoplasm as a product of nitrate reduction. In contrast, the electrogenic reduction of nitrite by the Nrf pathway provides a secondary source of energy during anaerobic growth and is consequently repressed by the NarL protein when the thermodynamically more favourable electron acceptor, nitrate, is available. Two short DNA sequences, 5'-TACCAT-3' and 5'-CTCCTT-3', were found in the promoters of operons known to be activated or repressed by the NarL protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Nitrite and Red Cell Function in Carp: Control Factors for Nitrite Entry, Membrane Potassium Ion Permeation, Oxygen Affinity and Methaemoglobin Formation

Abstract: Red cell function was studied in carp by a combination of in vivo and in vitro experiments with nitrite as the perturbing agent. In vivo accumulation of nitrite caused a marked increase in the red cell methaemoglobin content, and reduced the mean cellular volume. The oxygen affinity of unoxidized haemoglobin was strongly decreased, partly as result of the elevated concentration of cellular nucleoside triphosphates and haemoglobin associated with red cell shrinkage. Red cell pH was unchanged compared to controls, but reduced when referred to constant extracellular pH and O 2 saturation. The mean cellular K + content decreased, reflecting a K + loss from the red cells during their shrinkage. This K + loss contributed significantly to the large plasma hyperkalaemia during nitrite exposure. In vitro experiments revealed that nitrite influx into deoxygenated red cells was much larger than into oxygenated red cells. Nitrite permeation of the red cell membrane was not inhibited by DIDS and did not change extracellular pH. Methaemoglobin (MetHb) formation was more pronounced in deoxygenated blood than in oxygenated blood, but quasi-steady states were reached, reflecting a balance between nitrite-induced MetHb formation and the action of MetHb reductase. Red cells incubated in the oxygenated state released K + , whereas a net K + uptake occurred in deoxygenated cells. Nitrite did not change the K + loss from oxygenated cells, but shifted the K + uptake in deoxygenated cells to a pronounced K + release by the time high MetHb levels were reached. Both types of red cell K + release were inhibited by DIDS and appeared to occur via a route involving Band 3. The data are consistent with the hypothesis that a significant DIDS-sensitive K + efflux from the red cells occurs whenever a large fraction of the haemoglobin molecules assumes an R-like quaternary structure.

Toxicity of Ammonia and Nitrite to Penueus monodon Juveniles

Abstract: Pcnaeus monodon juveniles (35.4 ± 2.2 mm TL) were exposed to seawater (20 ppt) having different concentrations of total ammonia (NH3+ NH,+) and nitrite. Median lethal concentration (LC50) was determined with static-renewal tests. The LC50, of total ammonia-N, NH3-N and niMte-N on shrimps decreased with increase of exposure time. The 24, 48, 72, % and 120 h LC50 were 94.96, 61.09, 47.47 45.58 and 38.00 mg/L total ammonia-N (2.68, 1.73, 135, 1.29 and 1.08 mg/L NH3-N) and 215.85, 185.33, 88.54, 54.76 and 37.97 mg/L nitrite-N, respectively. The 144h LC50 of total ammonia-N and NH3-N was 36.71 mg/L and 1.04 mgL. The “threshold” of ammonia and nitrite was found at 144h and 120h respectively, from the toxicity curve approaching asymptote. A “safe value” was 3.7 mg/L total ammonia-N, 0.1 mg/L NH3-N (20 ppt, pH 7.70, 27C) and 3.8 mg/L nitrite-N for P. monodon juvenile.

A new facultatively nitrite oxidizing bacterium, Nitrobacter vulgaris sp. nov.

Abstract: A total of 17 facultatively lithoautotrophic strains of Nitrobacter were investigated. They all were found to be related on the species level by DNA hybridizations. The G+C content of DNA ranged between 58.9 and 59.9 mol %. The isolates originated from divers environments. The cells were 0.5−0.8×1.2−2.0 μm in size and motile by one polar to subpolar flagellum. Cell-division normally occurred by budding. Polar caps of intracytoplasmic membranes as well as carboxysomes were present. The cells tended to excrete extracellular polymers forming aggregates or biofilms. Heterotrophic growth was slower than mixotrophic but often faster than litoautotrophic growth. In the presence of nitrite and organic substances the organisms often showed diphasic growth. First nitrite and then the organic material was oxidized. In the absence of oxygen growth was possible by dissimilatory nitrate reduction. Nitrite, nitric and nitrous oxide as well as ammonia were formed. Depending on growth conditions the generation times varied from 12 to 140 h. The new Nitrobacter spec. may be one of the most abundant nitrite-oxidizing bacteria in soils, fresh waters and natural as well as artificial stones. For this organism the name Nitrobacter vulgaris is proposed. The type strain is filed with the culture collection of the Institut fur Allgemeine Botanik, Universitat Hamburg, FRG.

Inhibition of Nitrogen Fixation in Soybean Plants Supplied with Nitrate I. Nitrite Accumulation and Formation of Nitrosylleghemoglobin in Nodules

Abstract: The present investigation was undertaken in order to examine the influence on nitrogen fixation of the accumulation of nitrite, as result of the supply of exogenous nitrate, in soybean nodules, and to clarify the relationship between the inhibition of nitrogen fixation, the formation of nitrite in the nodule cytosol, and the decrease in leghemoglobin function due to the formation of LbNO under such conditions

Dietary intakes of some essential and non-essential trace elements, nitrate, nitrite and N-nitrosamines, by Dutch adults: estimated via a 24-hour duplicate portion study.

Abstract: Duplicate portions of 24‐hour diets of 110 adults have been analyzed for aluminium, cadmium, copper, lead, manganese, mercury, zinc, nitrate, nitrite and volatile N‐nitrosamines. The mean daily intake of copper (1.2 mg) is only about 50% of recommended values; mean daily intakes for manganese (3.3 mg) and zinc (8.4 mg) are adequate and marginal respectively with respect to recommended amounts. For the non‐essential elements Al, Cd, Hg and Pb, mean daily intakes of 3.1 mg, 0.01 mg, 0.002 mg and 0.034 mg were found, respectively. For Cd this amounts to 17% of the acceptable daily amount, for Al, Hg and Pb 5%, 5% and 8%, respectively. Since 1976–1978 the dietary intake of lead has been reduced by a factor three; for the other six elements daily dietary intakes are almost the same as in 1976–1978. Average nitrate intake was 52 mg NO− 3/day, about 25% of the ADI. Only 16 diets contained a measurable amount of nitrite. The highest daily intake (0.7 mg NO− 2) is less than 10% of the ADI. Volatile N‐nitrosamines ...

The analyses of KCL soil extracts for nitrate, nitrite and ammonium using a TRAACS 800 analyzer

Abstract: Potassium chloride extracts of soils are often coloured due to organic or colloidal matter. A dialyzer was used to remove these interferences and reduce the sensitivity of the method to attain the optimum range in concentration for the simultaneous determination of nitrate, nitrite and ammonium at an analysis rate of 100 samples per hour. Highly coloured plant extracts were also analysed without interference. Ammonium is determined by the Berthelot Reaction, through the formation of a blue coloured compound apparently related to indophenol from the reaction of ammonium and sodium phenoxide, followed by the addition of sodium hypochlorite. Sodium nitroprusside is added to intensify the blue colour. Nitrate is reduced to nitrite at pH 7.5 in a copper‐cadmium reductor coil. The nitrite produced reacts under acidic conditions with sulfanilamide to form a diazo compound that couples with N‐1‐Naphthylethylenediamine dihydrochloride to form a reddish‐purple azo dye measurable at 520 nm.

Evidence for the production of nitric oxide by activated macrophages treated with the antitumor agents flavone-8-acetic acid and xanthenone-4-acetic acid.

Abstract: Activated peritoneal macrophages, obtained from mice pretreated with Bacillus Calmette-Guerin, after exposure in vitro to flavone-8-acetic acid (FAA; NSC 347512) at a concentration of 890 microM, produce nitrite (3.7 nmol/10(6) cells), as measured 20 h later by the Griess reaction. Stimulation of nitrite production was inhibited at least 90% by NG-monomethylarginine (125 microM), suggesting that nitrite was formed via nitric oxide as a product of arginine metabolism. Stimulation was only partially inhibited by dexamethasone (0.1 microM). The ability of xanthenone-4-acetic acid (XAA) and three of its analogues to stimulate nitrite production was also investigated. 5,6-Dimethyl-XAA stimulated nitrite production (12.6 nmol/10(6) cells) at an optimal concentration of 80 microM, 8-methyl-XAA was without effect, and XAA and 5-methyl-XAA showed intermediate activity. The optimal in vitro drug concentrations for stimulation by FAA, XAA, and active XAA analogues correlated with the optimal in vivo dose required for the induction of either hemorrhagic necrosis or growth delay of s.c. Colon 38 tumors. These results strongly imply that FAA and active XAA derivatives function as low molecular weight stimulators of nitric oxide formation in macrophages, possibly acting on the same differentiation pathway as do endotoxin and tumor necrosis factor alpha. We suggest that nitric oxide, which is known to be toxic to tumor cells, contributes to the cytotoxic action of FAA and its analogues.

Influence of soil pH on the nitrate-reducing microbial populations and their potential to reduce nitrate to NO and N2O

Abstract: Slurries of an acid forest soil (pH 4.0) and two slightly alkaline agricultural soils (pH 7.6–7.8) were adjusted to pH values between 3.8 and 7.8 and tested for the nitrate-reducing potential; the perceptual production of nitrite. NO, N2O and NH4+; and the most probable number (MPN) counts of nitrate-reducing bacteria. As a general trend, pH had a 2-fold effect, i.e. nitrate-reducing potentials decreased with pH, whereas the proportions of NO, N2O and NH4+ production increased. Experiments with chloramphenicol indicated that this behaviour was due to adaptation of the resident bacterial activity rather than to population changes. The relatively high rates of NH4+ production indicated the presence of nitrate-ammonifying in addition to denitrifying bacteria. The population size of the nitrate-reducing bacteria was similar when MPN culture media with acid or neutral pH were used, but increased by 3 orders of magnitude when slurries of the acid soil were preincubated at neutral pH. The potential of the resident populations for nitrate reduction and growth populations for nitrate reduction and growth apparently was limited but not completely precluded by low soil pH. The acid forest soil did not contain a population that was specifically adapted to the low pH in situ.

Induction and activity of NO synthase in bone-marrow-derived macrophages are independent of Ca2+

Abstract: The aim of the present study was to analyse whether an increase in the intracellular free Ca2+ concentration ([Ca2+]i) plays a role as a signal mediating synthesis of nitric oxide (NO) in bone-marrow-derived macrophages, either by stimulating induction of NO synthase or by regulating the activity of the enzyme. Therefore we compared the effects of various synthetic analogues of bacterial lipopeptide and of lipopolysaccharide (LPS) on NO production (assessed as nitrite formation during an incubation for 24 h) and on [Ca2+]i [measured with the fluorescent probe indo-1 (1-[2-amino-5-(6-carboxyindol-2-yl)phenoxy]-2- 2-(2′-amino-5′-methylphenoxy)ethane-NNN′N′-tetra-acetic acid)]. Strongly dissociating effects were evoked on nitrite formation and on [Ca2+]i by the stimuli. LPS was preferentially effective on nitrite formation, whereas the Ca2+ ionophore ionomycin and AlF3 induced increases only in [Ca2+]i. The lipopeptides N-palmitoyl-(S)-[2,3-bis(palmitoyloxy)-(2RS)- propyl]-(R)-cysteinylalanylglycine, N-palmitoyl-(S)-[2,3-bis(palmitoyloxy)- (2RS)-propyl]-(R)-cysteinylseryl-lysyl-lysyl-lysine and (S)-(1,2- dicarboxyhexadecyl)ethyl-N-palmitoylcysteinylseryl-lysyl-lys yl-lysine stimulated both parameters, but the maximal effects on nitrite formation and the shape of the dose-response curves did not parallel the effects on [Ca2+]i. Reduction of extracellular Ca2+ with EGTA significantly inhibited increases in [Ca2+]i, but did not change nitrite formation. Furthermore, NO synthesis in the cytosolic fraction of stimulated macrophages was not affected by Ca2+ over the concentration range 10 nM-2 microM. We conclude that increases in [Ca2+]i are not required for NO production in bone-marrow-derived macrophages. Thus the cellular regulation of NO production strikingly differs from that in the vascular endothelium, brain and adrenal gland.

Modeling of Nitrification Under Substrate‐Inhibiting Conditions

Abstract: A mathematical model was developed for the biological-nitrification process. The model assumed two consecutive oxidation steps occurring under a substrate-inhibiting condition. The mathematical model was calibrated using data obtained from batch experiments performed on the contents of five chemostats operated to steady-state on a feed containing 1,000 mg/L of ammonia-nitrogen. In the batch experiments, initial ammonia concentrations ranging from 100 to 1,000 mg-N/L were used. Time-varying concentrations of ammonia and nitrite were collected until the oxidation of these constituents was complete. Parameter sets that optimized the fit on the mathematical model to the experimental data were obtained by nonlinear-regression analyses. The oxidation of ammonia to nitrite was well represented by the Haldane-inhibition model. The Haldane-inhibition model did not satisfactorily describe the oxidation of nitrite to nitrate. It was observed that the simultaneous presence of both nitrite and ammonia led to the inhibition of nitrite oxidation. Modification of the model to consider a revised inhibition mechanism that accounted for the observed behavior was quite successful for the interpretation of the nitrite-oxidation data.