Showing papers on "Nitrite published in 1991"

Pathway for Biodegradation of p-Nitrophenol in a Moraxella sp

Abstract: A Moraxella strain grew on p-nitrophenol with stoichiometric release of nitrite. During induction of the enzymes for growth on p-nitrophenol, traces of hydroquinone accumulated in the medium. In the presence of 2,2′-dipyridyl, p-nitrophenol was converted stoichiometrically to hydroquinone. Particulate enzymes catalyzed the conversion of p-nitrophenol to hydroquinone in the presence of NADPH and oxygen. Soluble enzymes catalyzed the conversion of hydroquinone to γ-hydroxymuconic semialdehyde, which was identified by high-performance liquid chromatography (HPLC)-mass spectroscopy. Upon addition of catalytic amounts of NAD+, γ-hydroxymuconic semialdehyde was converted to β-ketoadipic acid. In the presence of pyruvate and lactic dehydrogenase, substrate amounts of NAD were required and γ-hydroxymuconic semialdehyde was converted to maleylacetic acid, which was identified by HPLC-mass spectroscopy. Similar results were obtained when the reaction was carried out in the presence of potassium ferricyanide. Extracts prepared from p-nitrophenol-growth cells also contained an enzyme that catalyzed the oxidation of 1,2,4-benzenetriol to maleylacetic acid. The enzyme responsible for the oxidation of 1,2,4-benzenetriol was separated from the enzyme responsible for hydroquinone oxidation by DEAE-cellulose chromatography. The results indicate that the pathway for biodegradation of p-nitrophenol involves the initial removal of the nitro group as nitrite and formation of hydroquinone. 1,4-Benzoquinone, a likely intermediate in the initial reaction, was not detected. Hydroquinone is converted to β-ketoadipic acid via γ-hydroxymuconic semialdehyde and maleylacetic acid.

Interleukin-lβ-Induced Nitric Oxide Production in Isolated Rat Pancreatic Islets Requires Gene Transcription and May Lead to Inhibition of the Krebs Cycle Enzyme Aconitase

Abstract: The aim of this study was to characterize the dynamics and functional relevance of interleukin-1 beta (IL-1 beta)-induced nitric oxide production in isolated pancreatic islets. Thus, islets were isolated from adult rats, precultured for 3-5 days in medium RPMI-1640 plus 10% fetal calf serum, and then exposed to IL-1 beta for different time periods, after which islet nitrite production and aconitase activity were determined. IL-1 beta (5 ng/ml) did not increase islet nitrite production during the first hour of incubation. Moreover, the nitric oxide synthase inhibitor NG-monomethyl-L-arginine (Meth-arg; 5 mM) failed to prevent the initial (90 min) IL-1 beta-induced increase in islet insulin release. After 4, 7, and 24 h, however, nitrite production was increased by 50%, 93%, and 139%, respectively. Islet aconitase activity and glucose oxidation rates were decreased by 70% after incubation for 24 h with IL-1 beta. Both Meth-arg and N alpha-p-tosyl-L-lysine chloromethyl ketone (0.1 mM), a protease inhibitor, could completely counteract the IL-1 beta-induced increases in nitrite production and inhibition of aconitase activity and glucose oxidation rates. In a separate series of experiments, islets were incubated for 60 min with or without IL-1 beta and the RNA synthesis inhibitor actinomycin-D (5 micrograms/ml) and subsequently incubated for another 9 h without any additions. The presence of actinomycin-D during the 1-h IL-1 beta incubation period prevented the IL-1 beta-induced rise in nitrite production and the IL-1 beta-induced inhibition of aconitase activity and insulin release. It is concluded that IL-1 beta-induced nitric oxide production is a late event which requires gene transcription and does not mediate the initial stimulatory effects of IL-1 beta on beta-cell function. However, the gradually augmented rate of nitric oxide production may inhibit the enzyme aconitase, leading to a suppressed mitochondrial activity and a defective insulin release in response to nutrient secretagogues.

Killing of Plasmodium falciparum in vitro by nitric oxide derivatives

Abstract: We have investigated the in vitro susceptibility of the human malaria parasite Plasmodium falciparum to killing by nitric oxide and related molecules. A saturated solution of nitric oxide did not inhibit parasite growth, but two oxidation products of nitric oxide (nitrite and nitrate ions) were toxic to the parasite in millimolar concentrations. Nitrosothiol derivatives of cysteine and glutathione were found to be about a thousand times more active (50% growth inhibitory concentration, approximately 40 microM) than nitrite.

Biodegradation of 2,4-dinitrotoluene by a Pseudomonas sp.

Abstract: Previous studies of the biodegradation of nonpolar nitroaromatic compounds have suggested that microorganisms can reduce the nitro groups but cannot cleave the aromatic ring. We report here the initial steps in a pathway for complete biodegradation of 2,4-dinitrotoluene (DNT) by a Pseudomonas sp. isolated from a four-member consortium enriched with DNT. The Pseudomonas sp. degraded DNT as the sole source of carbon and energy under aerobic conditions with stoichiometric release of nitrite. During induction of the enzymes required for growth on DNT, 4-methyl-5-nitrocatechol (MNC) accumulated transiently in the culture fluid when cells grown on acetate were transferred to medium containing DNT as the sole carbon and energy source. Conversion of DNT to MNC in the presence of 18O2 revealed the simultaneous incorporation of two atoms of molecular oxygen, which demonstrated that the reaction was catalyzed by a dioxygenase. Fully induced cells degraded MNC rapidly with stoichiometric release of nitrite. The results indicate an initial dioxygenase attack at the 4,5 position of DNT with the concomitant release of nitrite. Subsequent reactions lead to complete biodegradation and removal of the second nitro group as nitrite.

Chemical removal of nitrate from water

Abstract: HIGH levels of nitrate in ground water can pose a serious health risk. Reduction of nitrate to nitrite in the gut may cause methemoglobinaemia1both in newborn infants and in adults deficient in glucose-phosphate dehydrogenase2. Under abnormal circumstances, reduction to nitrite can also occur in the stomach to form N-nitrosamines, a postulated cause of stomach cancer3. Nitrate outflow onto shallow continental shelves can promote nearshore algal blooms. Both natural and anthropogenic sources contribute to nitrate pollution. In the United States4 and Europe5, legislation now specifies a maximum permissible nitrate level in drinking water. Techniques such as selective ion exchange6, reverse osmosis, electrodialysis and distillation exist to transfer nitrate between two bodies of water, but only biological processes are presently available for nitrate destruction. Here I describe a chemical process in which aluminium powder reduces nitrate to ammonia, nitrogen and nitrite. In a pH range of 9 to 10.5, selective reduction of nitrate relative to sulphate is possible, and between pH 9.1 and 9.3, loss of the reductant through decomposition of water can be minimized to less than 2%. Subsequent control of pH and concentrations of dissolved aluminium, nitrite and ammonia should be possible at a realistic cost, making this process potentially useful for combating nitrate pollution.

Inhibition of Cryptococcus neoformans replication by nitrogen oxides supports the role of these molecules as effectors of macrophage-mediated cytostasis.

Abstract: Activated macrophages are able to inhibit the replication of intracellular microbes and tumor cells. In the murine system, this cytostatic effect is associated with the oxidation of L-arginine to L-citrulline, nitrite, and nitrate and is thought to be mediated by an intermediate of this reaction, possibly nitric oxide (NO.). By exposing replicating Cryptococcus neoformans cells to conditions under which NO. is chemically generated, we have observed a cytostatic effect similar to that caused by activated murine macrophages. Nitric oxide is formed as a decomposition product of nitrite salts in acidic, aqueous solutions. Although C. neoformans replicates well in the presence of high nitrite concentrations at physiologic pH, its growth in acidic media can be inhibited by the addition of low concentrations of sodium nitrite. The degree of cytostasis is dependent on both the pH and the nitrite concentration of the NO. generating solution. The cytostatic effector molecule appears to be a gas since, in addition to inhibiting C. neoformans replication in solution, it is able to exert its inhibitory effect across a gas-permeable but ion-impermeable membrane. At high nitrite concentrations, a fungicidal effect occurs. We propose that the growth inhibition of C. neoformans upon exposure to chemically generated NO. or some related oxide of nitrogen represents a cell-free system simulating the cytostatic effect of activated murine macrophages.

Levels of nitrite, nitrate, N-nitroso compounds, ascorbic acid and total bile acids in gastric juice of patients with and without precancerous conditions of the stomach

Abstract: To determine the relevance of gastric juice factors to gastric carcinogenesis, 56 patients with unoperated stomachs undergoing endoscopy for dyspepsia had gastric juice aspirated and analysed for pH, ascorbic acid, total bile acids, nitrite, nitrate and total nitroso compounds (NOCs). Plasma was obtained for vitamin C estimation. Antral and body biopsies were assessed for gastritis, Helicobacter pylori, atrophy and intestinal metaplasia (IM). Patients with chronic atrophic gastritis (n = 17) had lower gastric juice ascorbic acid concentrations (P less than 0.001), higher pH (P less than 0.05) and higher incidence of H. pylori infection (P less than 0.001) than normal subjects (n = 12). Patients with reflux gastritis (n = 9) had higher total bile acids (P less than 0.01). Patients with chronic gastritis and IM (n = 11) had higher gastric juice pH (P less than 0.01) and total bile acid concentrations (P less than 0.05), and lower gastric ascorbic acid concentrations (P less than 0.01) than those with chronic gastritis and no IM (n = 24). In chronic gastritis, high nitrite concentrations were associated with high pH (P less than 0.01). However, there were no significant differences in plasma vitamin C or gastric nitrite, nitrate or total NOC concentrations in relation to gastric histology. We conclude that the premalignant condition IM is associated with H. pylori infection, low gastric ascorbic acid levels and elevated total bile acids, but not to elevation in nitrite or total NOCs in fasting gastric juice.

Urinary nitrate excretion in relation to murine macrophage activation. Influence of dietary L-arginine and oral NG-monomethyl-L-arginine.

Abstract: Murine macrophage oxidation of L-arginine guanidino nitrogen to nitrite/nitrate yields an intermediate effector, possibly nitric oxide, with antimicrobial activity. Total body nitrogen oxidation metabolism (NOM) was measured in vivo by determining the urinary nitrate excretion of mice ingesting a chemically defined nitrite/nitrate-free diet. As reported previously, mycobacterial infection with bacillus Calmette-Guerin led to a large increase in urinary nitrate excretion. This increase was temporally related to macrophage activation in vivo. The substrate for macrophage nitrogen oxidation metabolism in vitro, L-arginine, was deleted from the diet without ameliorating the urinary nitrate excretion response induced by BCG. This suggested that L-arginine was synthesized endogenously because there are no other known natural substrates for NOM. A competitive inhibitor of NOM, the L-arginine analog, NG-monomethyl-L-arginine was fed to mice in their drinking water. NG-monomethyl-L-arginine ingestion blocked both basal and bacillus Calmette-Guerin-induced urinary nitrate excretion over a 2-4 week time span. These experimental conditions should prove useful for further investigation on the role of macrophage NOM in host defense against intracellular microorganisms.

L-arginine-dependent production of a reactive nitrogen intermediate by macrophages of a uricotelic species.

Abstract: L-arginine-dependent production of reactive nitrogen intermediates (RNIs: nitric oxide, nitrite, and nitrate) by mammalian macrophages has been proposed to occur via an L-arginine oxidative deimination pathway and is known to be responsible for certain antineoplastic and antimicrobial effector functions. The present study represents the first examination of this pathway in a non-mammalian vertebrate. Because chickens, unlike mammals, lack a urea cycle and are incapable of de novo synthesis of L-arginine, the possible existence of an avian macrophage pathway for production of RNIs is questionable. We have defined conditions under which chicken macrophages are able to produce nitrite. Sephadex-elicited chicken peritoneal macrophages required a bacterial lipopolysaccharide (LPS from Escherichia coli) signal to produce nitrite during 24 hour cultures in the presence of L-arginine. As little as 5 ng/ml LPS resulted in significant nitrite production in culture. The relationship of nitrite production to both LPS and L-arginine levels was dose-dependent. D-arginine was unable to substitute for L-arginine but also produced no inhibitory effect. In contrast, L-NG-monomethyl arginine showed a significant inhibitory effect on nitrite production. A virus-transformed chicken macrophage cell line, HD11, also produced nitrite in a dose-dependent manner relative to both LPS and L-arginine concentration. Concentrations as low as 5 ng/ml LPS and 0.1 mM L-arginine resulted in significant nitrite production, while maximum levels of nitrite production were obtained using greater than or equal to 0.5 micrograms/ml LPS and greater than or equal to 0.4 mM L-arginine. These results indicate that chicken macrophages can produce RNIs. This production is dependent upon activation and is influenced by local L-arginine concentration. Moreover, because the chicken does not possess the ability to synthesize arginine and has an absolute nutritional requirement for this amino acid, the chicken represents a highly controllable system to examine the in vivo effects of L-arginine on macrophage-related immune functions.

Photochemical Reduction of Nitrate and Nitrite by Manganese and Iron Porphyrins

Abstract: New nitrate and nitrite complexes of metalloporphyrins have been synthesized and crystallographically characterized, and their photochemistry has been examined. Irradiation of Mn(TPP)(NO 3 ) and Mn(TPP)(NO 2 ) (where TPP=5,10,15,20-tetraphenylporphyrinate(2-)) produces the high-valent metal-oxo species O=Mn IV (TPP) quantitatively, with quantum yields of 1.58×10 −4 and 5.30×10 −4 , respectively. This metal-oxo species is capable of oxidizing substrates, as demonstrated in reactions with styrene or triphenylphosphine

Nitric and nitrous oxide reductases are active under aerobic conditions in cells of Thiosphaera pantotropha.

Abstract: Use of Clark-type electrodes has shown that, in cells of Thiosphaera pantotropha, the nitrous oxide reductase is active in the presence of O2, and that the two gases involved (N2O, O2) are reduced simultaneously, but with mutual inhibition. Reduction of nitrate, or nitrite, to N2O under aerobic conditions involves NO as an intermediate, as judged by trapping experiments with the ferric form of extracellular horse heart cytochrome c and the demonstration that the cells possess a nitric oxide reductase activity. The overall conversion of nitrate to N2, the process of denitrification, under aerobic conditions, is thus not prevented by reaction of NO with O2 and depends upon a nitrous oxide reductase system which differs from that in other organisms by being neither directly inhibited nor inactivated by O2.

Photochemistry and environment Part XIV. Phototransformation of nitrophenols induced by excitation of nitrite and nitrate ions

Abstract: The excitation of NO2−, HNO2 or NO3− in the presence of nitrophenol induces hydroxylations in the ortho or para positions with respect to the phenol function. No nitration is observed in contrast with phenol and hydroxybiphenyls. The reaction can be attributed to hydroxyl radicals formed in the photolysis of NO2−, HNO2 and NO3−. With nitrite, the reaction is more efficient at 253.7 nm than at longer wavelengths. This effect is not observed with HNO2. When NO2− or HNO2 are excited in the presence of nitrophenol, the formation of dihydroxynitrobenzenes competes with the scavenging of hydroxyl radicals by nitrite ions (or HNO2) and the efficiency of the reaction is significantly influenced by the relative concentrations.

Health hazards of nitrate in drinking water

Abstract: Nitrate per se is not toxic, but is the precursor of nitrite which is produced through microbial reduction of nitrate in the intestine or in food preparations and which causes methemoglobinemia. Children exposed to excessive nitrate in their diet can have slightly retarded bodily growth and slower reflexes. The trouble is mainly confined to infants who are artificially fed with milk feeds made with water containing elevated nitrate levels. The exposure of the South African population to nitrates in drinking water is unknown, as are possible effects of it

Molecular mechanisms of nitrovasodilator bioactivation.

Abstract: All nitrovasodilators act intracellularly by a common molecular mechanism. This is characterized by the release of nitric oxide (NO). They are, thus, prodrugs or carriers of the active principle NO, responsible for endothelial controlled vasodilation. The rate of NO-formation strongly correlates with the activation of the soluble guanylate cyclase in vitro, resulting in a stimulation of cGMP synthesis. Nitrovasodilators thus are therapeutic substitutes for endogenous EDRF/NO. The pathways of bioactivation, nevertheless, differ substantially, depending on the individual chemistry of the nitrovasodilator. Besides NO, numerous other reaction products such as nitrite and nitrate anions are formed. The guanylate cyclase is only activated if NO is liberated. In the case of organic nitrates such as GTN, NO is only formed if certain thiol compounds are present as an essential cofactor. The rate of NO-formation correlates with the number of nitrate ester groups and proceeds with a simultaneous nitrite formation (with a ratio of 1:14 in the presence of cysteine). Nitrosamines such as molsidomine do not need thiol compounds for bioactivation. They directly liberate NO from the ring-open A-forms. This process basically depends on the presence of oxygen as electron acceptor from the sydnonimine molecule. Therefore, besides NO also superoxide radicals are formed, which may react with the generated NO under formation of nitrate ions. Organic nitrites (such as amyl nitrite) require the preceding interaction with a mercapto group to form a S-nitrosothiol intermediate, from which finally NO radicals are liberated. Nitrosothiols (like S-nitroso-acetyl-penicillamine) and sodium nitroprusside spontaneously release NO. The molecules themselves do not possess a direct enzyme activating potency. In the presence of thiol compounds organic nitrites (e.g., amyl nitrite) and nitrosothiols may act as intermediary products of NO generation.

NarK enhances nitrate uptake and nitrite excretion in Escherichia coli.

Abstract: narK mutants of Escherichia coli produce wild-type levels of nitrate reductase but, unlike the wild-type strain, do not accumulate nitrite when grown anaerobically on a glucose-nitrate medium. Comparison of the rates of nitrate and nitrite metabolism in cultures growing anaerobically on glucose-nitrate medium revealed that a narK mutant reduced nitrate at a rate only slightly slower than that in the NarK+ parental strain. Although the specific activities of nitrate reductase and nitrite reductase were similar in the two strains, the parental strain accumulated nitrite in the medium in almost stoichiometric amounts before it was further reduced, while the narK mutant did not accumulate nitrite in the medium but apparently reduced it as rapidly as it was formed. Under conditions in which nitrite reductase was not produced, the narK mutant excreted the nitrite formed from nitrate into the medium; however, the rate of reduction of nitrate to nitrite was significantly slower than that of the parental strain or that which occurred when nitrite reductase was present. These results demonstrate that E. coli is capable of taking up nitrate and excreting nitrite in the absence of a functional NarK protein; however, in growing cells, a functional NarK promotes a more rapid rate of anaerobic nitrate reduction and the continuous excretion of the nitrite formed. Based on the kinetics of nitrate reduction and of nitrite reduction and excretion in growing cultures and in washed cell suspensions, it is proposed that the narK gene encodes a nitrate/nitrite antiporter which facilitates anaerobic nitrate respiration by coupling the excretion of nitrite to nitrate uptake. The failure of nitrate to suppress the reduction of trimethylamine N-oxide in narK mutants was not due to a change in the level of trimethylamine N-oxide reductase but apparently resulted from a relative decrease in the rate of anaerobic nitrate reduction caused by the loss of the antiporter system.

Ferrous iron dependent nitric oxide production in nitrate reducing cultures of Escherichia coli

Abstract: l-Lactate-driven ferric and nitrate reduction was studied in Escherichia coli E4. Ferric iron reduction activity in E. coli E4 was found to be constitutive. Contrary to nitrate, ferric iron could not be used as electron acceptor for growth. “Ferric iron reductase” activity of 9 nmol Fe2+ mg-1 protein min-1 could not be inhibited by inhibitors for the respiratory chain, like Rotenone, quinacrine, Actinomycin A, or potassium cyanide. Active cells and l-lactate-driven nitrate respiration in E. coli E4 leading to the production of nitrite, was reduced to about 20% of its maximum activity with 5 mM ferric iron, or to about 50% in presence of 5 mM ferrous iron. The inhibition was caused by nitric oxide formed by a purely chemical reduction of nitrite by ferrous iron. Nitric oxide was further chemically reduced by ferrous iron to nitrous oxide. With electron paramagnetic resonance spectroscopy, the presence of a free [Fe2+-NO] complex was shown. In presence of ferrous or ferric iron and l-lactate, nitrate was anaerobically converted to nitric oxide and nitrous oxide by the combined action of E. coli E4 and chemical reduction reactions (chemodenitrification).

Anion chromatography using octadecylsilane reversed-phase columns coated with cetyltrimethylammonium and its application to nitrite and nitrate in seawater

Abstract: Low levels of NO 2 − and NO 3 − are directly determined by using a silicone-polymer-coated C 18 column with high anion-exchange capacity, O.1M NaCl eluent, and UV and amperometric detection