Showing papers on "Nitrite published in 1992"

Increased concentrations of nitrite in synovial fluid and serum samples suggest increased nitric oxide synthesis in rheumatic diseases.

Abstract: Cytokines induce nitric oxide synthesis by endothelial cells, macrophages and polymorphonuclear leucocytes, indicating a role for nitric oxide in inflammatory processes. Nitric oxide production was therefore measured indirectly as nitrite in serum and synovial fluid samples from patients with rheumatoid arthritis (RA) and osteoarthritis (OA) together with serum samples from healthy volunteers matched for age and sex. Serum nitrite concentrations in patients with RA and OA were significantly higher than in controls. In both disease groups synovial fluid nitrite was significantly higher than serum nitrite, implying nitric oxide synthesis by the synovium. Serum and synovial fluid nitrite concentrations in RA were also significantly higher than those in OA. These data show increased nitric oxide production in RA and OA and suggest a role for nitric oxide as an inflammatory mediator in rheumatic diseases.

Denitrification by fungi.

Abstract: Many fungi in the centre of the group of Fusarium and its teleomorphs were shown to be capable of reducing nitrite anaerobically to form nitric oxide (NO), nitrous oxide (N2O), and/or dinitrogen (N2). Several strains could reduce nitrate as well. Nitrous oxide was the major product of the reduction of nitrate or nitrite. Several fungi could also form N2. When [15]nitrite was used as substrate for the N2-forming dinitrification, 15N2O, 15NO, and 14N15N were obtained as the products. These results demonstrated that, unexpectedly, many fungi have denitrifying abilities. It was also shown that the fungal system contains a unique reaction, formation of a hybrid dinitrogen.

Dependence of the metabolism of nitric oxide (NO) in healthy human whole blood on the oxygenation of its red cell haemoglobin.

Abstract: Plasma or whole venous or arterialized blood from healthy human donors was incubated with NO (50-300 microM), and the resulting formation of methaemoglobin (MetHb), nitrosyl haemoglobin (HbNO), and plasma nitrite and nitrate were measured. In plasma, NO was converted to nitrite and nitrate in a ratio of 5:1. In arterial blood (O2 sat. 94-99%) NO was almost quantitatively converted to nitrate and MetHb. No nitrite was detected and HbNO formation was low. In venous blood (O2 sat. 36-85%) more HbNO and less nitrate was formed, in comparison to arterialized blood. We propose that NO liberated from endothelium of conductance and resistance vessels is taken up by red blood cells and inactivated by HbO2 via stoichiometric conversion to MetHb and nitrate.

L-arginine transport is increased in macrophages generating nitric oxide.

Abstract: Transport of L-arginine and nitrite production were examined in the murine macrophage cell line J774. Bacterial lipopolysaccharide (LPS) induced a dose- and time-dependent stimulation of nitrite production, which was further increased in the presence of interferon-gamma. Nitrite synthesis was absolutely dependent on extracellular L-arginine and inhibited in the presence of L-lysine or L-ornithine. In unactivated J774 cells L-arginine transport was saturable, with an apparent Km of 0.14 +/- 0.04 mM and Vmax. of 15 +/- 2 nmol/h per 10(6) cells. LPS (1 microgram/ml) induced a time-dependent stimulation of L-arginine transport, and after 24 h the Vmax. increased to 34 +/- 2 nmol/h per 10(6) cells. These findings indicate that activation of J774 cells with LPS produces an increase in both L-arginine transport and nitrite synthesis. The elevated rate of L-arginine transport in activated J774 cells may provide a mechanism for sustained substrate supply during enhanced utilization of L-arginine for the generation of NO.

Oxidation of inorganic nitrogen compounds as energy source.

Abstract: This chapter covers one of the microbiological steps of the nitrogen cycle, nitrification, which is the biological oxidation of reduced forms of inorganic nitrogen to nitrite and nitrate. Nitrifying bacteria use the oxidation of inorganic nitrogen compounds as their major energy source. Reactions are catalyzed by two physiological groups of bacteria: ammonia-oxidizing bacteria, which gain energy from oxidation of ammonia to nitrite, and nitrite-oxidizing bacteria, which thrive by oxidizing nitrite to nitrate. Because of the toxic nature of nitrite, its rapid conversion to nitrate, assimilated by plants and microorganisms, is essential. Ammonia oxidizers are lithoautotrophic organisms using carbon dioxide as the main carbon source; ammonia monooxygenase oxidizes ammonia to hydroxylamine, which is convertedtonitritebythehydroxylamineoxidoreductase.When grown lithotrophically with nitrite, nitrite is oxidized to nitrate by the nitrite oxidoreductase and the oxygen atom in the nitrate molecule is derived from water. The enzyme also reduces nitrite to nitrate when Nitrobacter strains are grown heterotrophically in the presence of nitrate. Detailed schemes for electron flow and energy transduction as well as energy generation schemes are outlined and the role of nitrifying bacteria in the environment highlighted. The two groups of nitrifying bacteria are phylogenetically unrelated, as they are found in different classes of Proteobacteria and members of the nitrite oxidizers are even found in different phyla. This chapter also covers the physiology and phylogeny of recently detected anaerobic ammonium-oxidizing deep-branching members of the phylum Planctomycetes and of Nitrosomonas eutropha.

Degradation of 2,4-dinitrotoluene by the lignin-degrading fungus Phanerochaete chrysosporium

Abstract: Under ligninolytic conditions, the white rot basidiomycete Phanerochaete chrysosporium mineralizes 2,4-dinitrotoluene (I) The pathway for the degradation of I was elucidated by the characterization of fungal metabolites and oxidation products generated by lignin peroxidase (LiP), manganese peroxidase (MnP), and crude intracellular cell extracts The multistep pathway involves the initial reduction of I to yield 2-amino-4-nitrotoluene (II) II is oxidized by MnP to yield 4-nitro-1,2-benzoquinone (XII) and methanol XII is then reduced to 4-nitro-1,2-hydroquinone (V), and the latter is methylated to 1,2-dimethoxy-4-nitrobenzene (X) 4-Nitro-1,2-hydroquinone (V) is also oxidized by MnP to yield nitrite and 2-hydroxybenzoquinone, which is reduced to form 1,2,4-trihydroxybenzene (VII) 1,2-Dimethoxy-4-nitrobenzene (X) is oxidized by LiP to yield nitrite, methanol, and 2-methoxy-1,4-benzoquinone (VI), which is reduced to form 2-methoxy-1,4-hydroquinone (IX) The latter is oxidized by LiP and MnP to 4-hydroxy-1,2-benzoquinone, which is reduced to 1,2,4-trihydroxybenzene (VII) The key intermediate 1,2,4-trihydroxybenzene is ring cleaved by intracellular cell extracts to produce, after reduction, beta-ketoadipic acid In this pathway, initial reduction of a nitroaromatic group generates the peroxidase substrate II Oxidation of II releases methanol and generates 4-nitro-1,2-benzoquinone (XII), which is recycled by reduction and methylation reactions to regenerate intermediates which are in turn substrates for peroxidase-catalyzed oxidation leading to removal of the second nitro group Thus, this unique pathway apparently results in the removal of both aromatic nitro groups before ring cleavage takes place

Reduction of nitrate and nitrite in water by immobilized enzymes

Abstract: NITRATE, a common and serious contaminant of ground water, is removed at present either by physicochemical methods that do not degrade it, or via degradation by microorganisms, which is a slow process1. We report here a rapid and efficient process for nitrate removal which involves catalytic reduction by immobilized enzymes. The reduction is driven by an electrical current, and results in complete conversion of nitrate to N2 without residues. Our electro-bioreactor was constructed by co-immobilizing the enzymes (purified NADH: nitrate reductase from Zea mays2 and crude nitrite reductase and N2O reductase from Rhodop-seudomonas3) with electron-carrying dyes in a polymer matrix, which was then attached in thin layers to the surface of the cathode. Nitrate-laden water is pumped past the anode and through the active matrix on the cathode while a low voltage is applied, resulting in two-stage nitrate reduction to N2 via nitrite. The enzyme activity is higher in the co-immobilized state than in free solution. In principle, such electro-bioreactors could be developed for removal of other water contaminants such as pesticides, if appropriate enzymes and cofactors can be identified.

Denitrification in anaerobic digesters: Possibilities and influence of wastewater COD/N‐NOX ratio

Abstract: Laboratory‐scale completely‐stirred anaerobic digesters were fed with synthetic wastewaters containing nitrate and nitrite and with glucose as the only source of organic carbon in order to investigate and compare the denitrification potentials of anaerobic digesters in the presence of nitrate and nitrite. Varying the input nitrate and nitrite concentration at fixed COD and HRT, methane production without denitrification occurred at COD/N‐NOX > 53; denitrification and methane production at 8.86 ≤ COD/N‐NOX ≤ 53 and only denitrification at COD/N‐NOX 53, ammonification appeared to be the main nitrate and nitrite reduction pathway. The successful competition of ammonia formers over the true denitrifiers at high ratios was attributed to the low initial nitrate and nitrite concentrations.

Effects of nitrate and nitrite on dissimilatory iron reduction by Shewanella putrefaciens 200.

Abstract: The inhibitory effects of nitrate (NO3-) and nitrite (NO2-) on dissimilatory iron (FE3+) reduction were examined in a series of electron acceptor competition experiments using Shewanella putrefaciens 200 as a model iron-reducing microorganism. S. putrefaciens 200 was found to express low-rate nitrate reductase, nitrite reductase, and ferrireductase activity after growth under highly aerobic conditions and greatly elevated rates of each reductase activity after growth under microaerobic conditions. The effects of NO3- and NO2- on the Fe3+ reduction activity of both aerobically and microaerobically grown cells appeared to follow a consistent pattern; in the presence of Fe3+ and either NO3- or NO2-, dissimilatory Fe3+ and nitrogen oxide reduction occurred simultaneously. Nitrogen oxide reduction was not affected by the presence of Fe3+, suggesting that S. putrefaciens 200 expressed a set of at least three physiologically distinct terminal reductases that served as electron donors to NO3-, NO2-, and Fe3+. However, Fe3+ reduction was partially inhibited by the presence of either NO3- or NO2-. An in situ ferrozine assay was used to distinguish the biological and chemical components of the observed inhibitory effects. Rate data indicated that neither NO3- nor NO2- acted as a chemical oxidant of bacterially produced Fe2+. In addition, the decrease in Fe3+ reduction activity observed in the presence of both NO3- and NO2- was identical to the decrease observed in the presence of NO2- alone. These results suggest that bacterially produced NO2- is responsible for inhibiting electron transport to Fe3+.

Cytokines and Lipopolysaccharide Induce Nitric Oxide Synthase in Cultured Rat Pulmonary Artery Smooth Muscle

Abstract: In the current study, we describe cytokine and Escherichia coli lipopolysaccharide (LPS) induction of nitric oxide (NO) synthase mRNA levels in cultured smooth muscle from rat pulmonary artery (RPASM). Exposure of RPASM to interleukin-1β, interferon-γ, or LPS alone did not significantly affect NO synthesis, as determined by nitrite concentrations in media. Exposure to tumor necrosis factor-α caused a modest (2×) increase in nitrite production. In contrast, exposure to a combination of the above three cytokines and LPS caused a large increase in NO synthesis. Exposure of RPASM to this combination caused an increase in mRNA levels of NO synthase (as described by Northern blot analysis with 32P-cDNA probe to an inducible form of NO synthase present in murine macrophages) that was apparent as early as 4 h. Expression of the induced gene product after exposure to the cytokine and LPS mixture was evident by significant increases in nitrite production at 12 h. Production of nitrite was completely abolished in th...

The impact of organic matter on nitric oxide formation by Nitrosomonas europaea

Abstract: Chemolithoautotrophically growing cells of Nitrosomonas europaea quantitatively oxidized ammonia to nitrite under aerobic conditions with no loss of inorganic nitrogen. Significant inorganic nitrogen losses occurred when cells were growing mixotrophically with ammonium, pyruvate, yeast extract and peptone. Under oxygen limitation the nitrogen losses were even higher. In the absence of oxygen pyruvate was metabolized slowly while nitrite was consumed concomitantly. Nitrogen losses were due to the production of nitric oxide and nitrous oxide. In mixed cultures of Nitrosomonas and Nitrobacter, strong inhibition of nitrite oxidation was reproducibly measured. NO and ammonium were not inhibitory to Nitrobacter. First evidence is given that hydroxylamine, the intermediate of the Nitrosomonas monooxygenase-reaction, is formed. 0.2 to 1.7 μM NH2OH were produced by mixotrophically growing cells of Nitrosomonas and Nitrosovibrio. Hydroxylamine was both a selective inhibitory agent to Nitrobacter cells and a strong reductant which reduced nitrite to NO and N2O. It is discussed whether chemodenitrification or denitrification is the most abundant process for NO and N2O production of Nitrosomonas.

Decrease of Nitrate Reductase Activity in Spinach Leaves during a Light-Dark Transition

Abstract: In leaves of spinach plants (Spinacia oleracea L.) performing CO(2) and NO(3) (-) assimilation, at the time of sudden darkening, which eliminates photosystem I-dependent nitrite reduction, only a minor temporary increase of the leaf nitrite content is observed. Because nitrate reduction does not depend on redox equivalents generated by photosystem I activity, a continuation of nitrate reduction after darkening would result in a large accumulation of nitrite in the leaves within a very short time, which is not observed. Measurements of the extractable nitrate reductase activity from spinach leaves assayed under standard conditions showed that in these leaves the nitrate reductase activity decreased during darkening to 15% of the control value with a half-time of only 2 minutes. Apparently, in these leaves nitrate reductase is very rapidly inactivated at sudden darkness avoiding an accumulation of the toxic nitrite in the cells.

Nitrite oxidoreductase from nitrobacter hamburgensis redox centers and their catalytic role

Abstract: Nitrite oxidoreductase was isolated from mixotrophically grown cells of Nitrobacter hamburgensis. The enzyme purified from heat treated membranes was homogeneous by the criteria of polyacrylamide gel electrophoresis and size exclusion chromatography. The monomeric form consisted of two subunits with Mr 115000 and 65000, respectively. The dimeric form of the enzyme contained 0.70 molybdenum, 23.0 iron, 1.76 zinc, and 0.89 copper. The catalytically active enzyme was investigated by visible and electron paramagnetic resonance spectroscopy (EPR) under oxidizing (as isolated), reducing (dithionite), and turnover (nitrite) conditions. As isolated the enzyme exhibited a complex set of EPR signals between 5–75 K, originating from several ironsulfur and molybdenum (V) centers. Addition of the substrate nitrite, or the reducing agent dithionite resulted in a set of new resonances. The molybdenum and the iron-sulfur centers of nitrite oxidoreductase from Nitrobacter hamburgensis were involved in the transformation of nitrite to nitrate.

Inhibition of tobacco nitrite reductase activity by expression of antisense RNA

Abstract: Summary A tobacco nitrite reductase (NiR) cDNA and its corresponding gene were isolated from cDNA and genomic libraries. An NiR antisense mRNA was expressed in transgenic tobacco under the control of a double 35S promoter. Transformants were obtained on a medium containing ammonium as the sole source of nitrogen. One plant growing normally on ammonium but displaying drastically reduced development and chlorotic leaves when grown on nitrate as the sole source of nitrogen was studied further. This plant accumulated nitrite fivefold over wild-type level and showed reduced amounts of ammonium (11% wild-type level), glutamine (19%), and total protein (8%). NiR mRNA and activity were below detectable levels. Under these conditions, nitrate reductase (NR) activity and mRNA were overexpressed, suggesting that N-metabolites resulting from nitrate reduction are responsible for the repression of the expression of the NR gene, independently from the presence or absence of a functional NR protein.

Anaerobic metabolism of Nitrosomonas europaea

Abstract: Nitrosomonas europaea is capable of maintaining an anaerobic metabolism, using pyruvate as an electron donor and nitrite as an electron acceptor; utilization of nitrite depends upon supply of both pyruvate and ammonia. The role of ammonia in this reaction was not determined. N europaea also assimilates CO2 anaerobically into cell material in the presence of nitrite (0.5–1.0 mM), pyruvate and ammonia. This reaction was partially inhibited by nitrite which apparently competed with CO2 for reducing power. Anaerobic “nitrite respiration” is sensitive to ionophores, FCCP being the most effective.

Trinitrotoluene (TNT) as a sole nitrogen source for a sulfate-reducing bacterium Desulfovibrio sp. (B strain) isolated from an anaerobic digester.

Abstract: A sulfate-reducing bacterium (SRB),Desulfovibrio sp. (B strain), isolated from a continuous anaerobic digester (Boopathy and Daniels, Current Microbiology, 23:327–332, 1991) was found to use 2,4,6-trinitrotoluene (TNT) as sole nitrogen source. This bacterium also used nitrate, nitrite, and ammonium as nitrogen source. A long lag period was noticed when TNT or nitrite was used as nitrogen source. Nitrate, nitrite and TNT also served as electron acceptor in the absence of sulfate for this bacterium. Under nitrogen-limiting condition, 100% removal of TNT was observed within 8 days of incubation. The main intermediate observed was diaminonitrotoluene, which was further converted to toluene via triaminotoluene by reductive deamination process. Under nitrogen-rich conditions (presence of ammonium), TNT was converted to diaminonitrotoluene, and toluene was not produced. This isolate did not degrade TNT all the way to CO2. This study demonstrated the possibility of using this isolated to decontaminate the soil and water contaiminated with TNT under anaerobic conditions.

Heterotrophic nitrification and aerobic denitrification in Alcaligenes faecalis strain TUD.

Abstract: Heterotrophic nitrification and aerobic and anaerobic denitrification byAlcaligenes faecalis strain TUD were studied in continuous cultures under various environmental conditions. Both nitrification and denitrification activities increased with the dilution rate. At dissolved oxygen concentrations above 46% air saturation, hydroxylamine, nitrite and nitrate accumulated, indicating that both the nitrification and denitrification were less efficient. The overall nitrification activity was, however, essentially unaffected by the oxygen concentration. The nitrification rate increased with increasing ammonia concentration, but was lower in the presence of nitrate or nitrite. When present, hydroxylamine, was nitrified preferentially. Relatively low concentrations of acetate caused substrate inhibition (KI=109 μM acetate). Denitrifying or assimilatory nitrate reductases were not detected, and the copper nitrite reductase, rather than cytochrome cd, was present. Thiosulphate (a potential inhibitor of heterotrophic nitrification) was oxidized byA. faecalis strain TUD, with a maximum oxygen uptake rate of 140–170nmol O2·min-1·mg prot-1. Comparison of the behaviour ofA. faecalis TUD with that of other bacteria capable of heterotrophic nitrification and aerobic denitrification established that the response of these organisms to environmental parameters is not uniform. Similarities were found in their responses to dissolved oxygen concentrations, growth rate and ammonia concentration. However, they differed in their responses to externally supplied nitrite and nitrate.

Bacterial nitrite-reducing enzymes

Abstract: The enzymic reduction of nitrite takes place in a wide range of bacteria and is found to occur in denitrifying, assimilatory and dissimilatory pathways. In this review we describe the major molecular characteristics of the various enzymes employed in each of these processes.

Co-denitrification by the denitrifying system of the fungus Fusarium oxysporum

Abstract: Nitrogen compounds such as azide, salicylhydroxamic acid, and possibly ammonium ions were converted to nitrous oxide (N2O) or dinitrogen (N2) by Fusarium oxysporum under denitrifying conditions. Nitrogen atoms in these compounds were combined with another nitrogen atom from nitrite to form a hybrid N2O species. The fungus exhibited much higher converting activities as compared with similar reactions catalyzed by bacterial denitrifiers. We thus propose the phenomenon be called co-denitrification, which means that such nitrogen compounds are denitrified by the system induced by nitrite (or nitrate) but are incapable by themselves of inducing the denitrifying system.

Electrochemical reduction of nitrogen oxyanions in 1 M sodium hydroxide solutions at silver, copper and CuInSe2 electrodes

Abstract: The reduction of nitrate and nitrite ions was studied in 1m NaOH supporting electrolyte. Voltammetric investigations show that, on silver cathodes, nitrate reduction begins at potentials about 500 mV more positive than nitrite reduction, the latter being superimposed on hydrogen evolution. Electrolyses of nitrate solutions at −1.4V/sce give nitrite with good selectivity. On copper cathodes, nitrate and nitrite reductions occur in the same region of potentials and show similar voltammetric profiles. The dominant product of nitrite reduction is ammonia, whereas nitrate may be reduced to nitrite at −1.1 V/sce and to ammonia with high yields at −1.4 V/sce. Reduction of nitrogen oxyanions may also be performed on CuInSe2 (photo)cathodes. Photoassisted reductions of nitrate performed on p-CuInSe2 at −1.4 V/sce gave mixtures of ammonia, nitrite and hydrogen.

Mechanistic probes of N-hydroxylation of L-arginine by the inducible nitric oxide synthase from murine macrophages.

Abstract: NG-Hydroxy-L-arginine, [15N]-NG-hydroxy-L-arginine, and NG-hydroxy-NG- methyl-L-arginine were used as mechanistic probes of the initial step in the reaction catalyzed by nitric oxide synthase isolated from murine macrophages. NG-Hydroxy-L-arginine was found to be a substrate for nitric oxide synthase with a Km equal to 28.0 microM, yielding nitric oxide and L-citrulline. NADPH was required for the reaction and (6R)-tetrahydro-L-biopterin enhanced the initial rate of nitric oxide formation. The stoichiometry of NG-hydroxy-L-arginine loss to L-citrulline and nitric oxide (measured as nitrite and nitrate) formation was found to be 1:1:1. NG-Hydroxy-L-arginine was also observed in small amounts from L-arginine during the enzyme reaction. Studies with [15N]-NG-hydroxy-L-arginine indicated that the nitrogen in nitric oxide is derived from the oxime nitrogen of [15N]-NG-hydroxy-L- arginine. NG-Hydroxy-NG-methyl-L-arginine was found to be both a reversible and an irreversible inhibitor of nitric oxide synthase, displaying reversible competitive inhibition with K(i) equal to 33.5 microM. As an irreversible inhibitor, NG-hydroxy-NG-methyl-L-arginine gave kinact equal to 0.16 min-1 and KI equal to 26.5 microM. This inhibition was found to be both time- and concentration-dependent as well as showing substrate protection against inactivation. Gel filtration of an NG-hydroxy-NG-methyl-L-arginine-inactivated nitric oxide synthase failed to recover substantial amounts of enzyme activity.