Showing papers on "Nitrite published in 1973"

Mechanism of tolerance development to organic nitrates

Abstract: Tolerance to the vasodilator activity of organic nitrates appears to involve an alteration in a receptor in vascular smooth muscle. An in vitro model of nitrate tolerance was developed by incubation of rabbit thoracic aorta with organic nitrate at alkaline pH, producing a time- and concentration-dependent decrease in sensitivity to glyceryl trinitrate. Cross-tolerance is observed to all organic nitrates studied but not to nonnitrate vasodilators. When aortic strips are incubated at alkaline pH, nitrite formation is enhanced and tissue SH levels decrease. It s proposed that organic nitrate tolerance involves the oxidation of a critical sulfhydryl in the glyceryl trinitrate "receptor." This hypothesis is supported by the reversal of both in vitro - and in vivo -induced glyceryl trinitrate tolerance by the disulfide reducing agent, dithiothreitol.

Anaerobic nitrite production by plant cells and tissues: evidence for two nitrate pools.

Abstract: Tobacco (Nicotiana tabacum L. cv. Xanthi) XD cells containing nitrate and nitrate reductase stopped producing nitrite after approximately 1 hour when incubated under anaerobic conditions. The cessation of nitrite production was not due to an inactivation of the nitrate reducing system. This was shown by the ability of the cells to resume anaerobic nitrite production at a rate similar to the initial rate of nitrite production upon exposure to nitrate, monohydroxy alcohols or pyrazole. Cessation of nitrite production also could not be attributed to leakage of nitrate from the cells. Although some nitrate did leak from the cells, most of the nitrate was still in the cells by the time anaerobic nitrite production ceased. We infer the existence of a small metabolic pool and a large storage pool of nitrate, such that nitrite production ceases when the metabolic pool is depleted of nitrate. The metabolic pool of nitrate in tobacco cells decreased 170-fold as the culture aged from 3 to 5 days. However, total cellular nitrate during this period remained relatively constant.Anaerobic nitrite production by barley (Hordeum vulgare) aleurone layers and corn (Zea mays) leaf sections also ceased after only a small fraction of endogenous nitrate was reduced and resumed again upon addition of exogenous nitrate. In contrast to that found with tobacco cells, the metabolic pool of nitrate in corn leaf sections remained constant with age, while total endogenous nitrate increased. These results were interpreted to mean that higher plants in general contain metabolic and storage pools of nitrate, the properties of which vary with species and physiological variables.

Effect of sodium nitrite and sodium nitrate on botulinal toxin production and nitrosamine formation in wieners.

Abstract: Wieners were formulated and processed approximating commercial conditions as closely as possible. Twenty-four batches of product were made with the addition of six levels of sodium nitrite (0, 50, 100, 150, 200, and 300 μg/g), four levels of sodium nitrate (0, 50, 150, and 450 μg/g), and two levels of Clostridium botulinum (0 and 620 spores/g). After formulation, processing, and vacuum packaging, portions of each batch were incubated at 27 C or held for 21 days at 7 C followed by incubation at 27 C for 56 days. The latter storage condition approximated distribution of product through commercial channels and potential temperature abuse at the consumer level. Samples were analyzed for botulinal toxin, nitrite, and nitrate levels after 3, 7, 14, 21, 28, and 56 days of incubation. When nitrite was not added, toxic samples were detected after 14 days of incubation at 27 C. At the lowest level of nitrite added (50 μg/g), no toxic samples were observed until 56 days of incubation. Higher levels of nitrite completely inhibited toxin production throughout the incubation period. Nine uninoculated samples, representing various levels and combinations of nitrite and nitrate, were evaluated organoleptically. The flavor quality of wieners made with nitrite was judged significantly higher (P = 0.05) than of wieners made without nitrite. The nine samples were negative for 14 volatile nitrosamines at a sensitivity level of 10 ng/g. The results indicated that nitrite effectively inhibited botulinal toxin formation at commercially employed levels in wieners and that detectable quantities of nitrosamines were not produced during preparation and processing of the product for consumption.

The lower electronic states of nitrite and nitrate ion, nitromethane, nitramide, nitric acid, and nitrate esters

Abstract: CNDO/s–CI calculations are performed for the series of molecules: nitrite ion, nitromethane, nitramide, ethyl nitrate, methyl nitrate, nitric acid, and nitrate ion. The high intensity transitions, which occur near 6.5 eV in these molecules, are assigned to a transition to the 11B2(π0π*) state. The low intensity transitions, which occur below 6.5 eV, are assigned to transitions to 11B1(σ1π*) and 11A2(n 0π*) states. The 11A2(n 0π*) state remains at close to the same energy, 4.5 eV, throughout the series; whereas, the 11B1(σ1π*) state goes to increasingly high energy along the series. In nitrate ion, the 11A1(πD π*) and 21A2(σπ*) states, which lie above 6.5 eV in the other molecules, become degenerate with the 11B2(π0π*) and 11B1(σ1π*) states, respectively. Transitions to the 11A1(πD π*) state, which goes to lower energy across the series, may account for the high energy tail observed on transitions to the 11B2(π0π*) state. The first triplet state is assigned to the 13B1(σ1π*) and 13A2(n 0π*) state in nitrite and nitrate ion. respectively, the 13B1(σ1π*) state in nitromethane and the 13B2(π0π*) state in the nitric esters and nitric acid. The trends in the energies of these states along the series are related to the increasing electronegativity of the donor group attached to the nitro group. The 11,3A1(πD π*) states are characterized as intramolecular charge transfer states, which may be unstable to dissociation into donor and nitro group free radicals.

Effect of Nitrite and Nitrate on Toxin Production by Clostridium botulinum and on Nitrosamine Formation in Perishable Canned Comminuted Cured Meat

Abstract: Comminuted ham was formulated with different levels of sodium nitrite and nitrate, inoculated with Clostridium botulinum, and pasteurized to an internal temperature of 68.5 C. When added to the meat, nitrite concentrations decreased, and cooking had little effect on them. Nitrite concentrations decreased more rapidly during storage at 27 than at 7 C; however they remained rather constant at formulated levels throughout the experiment at both incubation temperatures. The level of nitrite added to the meat greatly influenced growth and toxin production of C. botulinum. The concentration of nitrite necessary to effect complete inhibition was dependent on the inoculum level. With 90 C. botulinum spores/g of meat, botulinum toxin developed in samples formulated with 150 but not with 200 μg of nitrite per g of meat. At a spore level of 5,000/g, toxin was detected in samples with 400 but not with 500 μg of nitrite per g of the product incubated at 27 C. At lower concentrations of nitrite, growth was retarded at both spore levels. No toxin developed in samples incubated at 7 C. Nitrate showed a statistically significant inhibitory effect at a given nitrite level; however, the effect was insufficient to be of practical value. Analyses for 14 volatile nitrosamines from samples made with varying levels of nitrite and nitrate were negative at a detection level of 0.01 μg of nitrite or nitrate per g of meat.

Degradation of parathion by bacteria isolated from flooded soil.

Abstract: Two bacteria, Bacillus sp. and Pseudomonas sp., were isolated from parathionamended flooded alluvial soil which exhibited parathion-hydrolyzing ability. Bacillus sp. readily liberated nitrite from the hydrolysis product, p-nitrophenol, but not from intact parathion. Pseudomonas sp. hydrolyzed parathion and then released nitrite from p-nitrophenol. These studies establish bacterial degradation of parathion past the p-nitrophenol stage to the end product, nitrite.

Protective Effect of Ascorbic Acid on Hepatotoxicity Caused by Sodium Nitrite Plus Aminopyrine

Abstract: The oral treatment of rats with sodium ascorbate in combination with sodium nitrite and aminopyrine prevents the rise in serum alanine aminotransferase (EC 2.6.1.2) observed when nitrite and aminopyrine are given alone. Ascorbic acid also affords protection, whereas dehydroascorbic acid exerts no protective effect.

Malignant tumours of liver and lung in rats fed aminopyrine or heptamethyleneimine together with nitrite.

Abstract: SOME human cancer might be caused by nitrosamines formed in the gastrointestinal tract from nitrite in the food and secondary or tertiary amines ingested deliberately or incidentally1–3. This hypothesis was supported by experiments in which rats fed with nitrite and secondary amines developed the same type of tumours as after treatment with the respective nitrosamines4.

Microbial formation of nitrosamines in vitro.

Abstract: Mortierella parvispora and an unidentified bacterium converted trimethylamine to dimethylamine, and the bacterium (but not the fungus) formed dimethylnitrosamine in the presence of nitrite Dimethylnitrosamine also appeared in cell suspensions of Escherichia coli and Streptococcus epidermidis and in hyphal mats of Aspergillus oryzae incubated with dimethylamine and nitrate Suspensions of a number of microorganisms produced N-nitrosodiphenylamine from diphenylamine and nitrite at pH 75, and soluble enzymes catalyzing the N-nitrosation of diphenylamine were obtained from two of these organisms In the presence of these enzymes, several dialkylamines were converted to the corresponding N-nitroso compounds

Formation of Nitrosamines in a Meat Curing Mixture

Abstract: TRACE amounts of certain N-nitrosamines, well known carcinogens, in foods, especially nitrite-treated meat and fish products, have caused a great deal of concern1–3. These compounds are usually formed from the interactions of nitrite and secondary or tertiary amines4–5. Recent studies, however, have shown that certain naturally occurring quaternary ammonium compounds can also react with nitrite to form nitrosamines6. Of the known nitrosamines dimethylnitrosamine (DMN) and nitrosopyrrolidine (NPy) are the two compounds which have been most frequently found to be present in cured meat products2,3,7,8. NPy is formed during frying of bacon but its presence in other cured meat products has not been reported.

Stabilization of solutions of 3-isothiazolones employing certain metal nitrates and nitrites

Abstract: Solution of 3-isothiazolones are stabilized against chemical decomposition of the isothiazolone by adding thereto a metal nitrate or a metal nitrite.

Studies on Horseradish Peroxidase. XII. A Kinetic Study of the Oxidation of Sulfite and Nitrite by Compounds I and II

Abstract: The kinetics of the oxidation of sulfite and nitrite by horseradish peroxidase compounds I and II have been studied as a function of pH at 25° and ionic strength 0.11. The pH dependence of the rate...

Inhibition of methane formation in soil by various nitrogen-containing compounds

Abstract: The evolution of methane from soil samples under anaerobic conditions was suppressed by adding nitrogen-containing chemicals. Nitrate caused the strongest inhibition of CH4 formation followed with decreasing efficiency by nitrite, nitric oxide and nitrous oxide; ammonium sulfate and hydroxylamine did not have an influence. It was also observed that organic substances in relation to their structure and concentration influence the evolution of CH4.

Separation of soluble denitrifying enzymes and cytochromes from Pseudomonas perfectomarinus.

Abstract: Nitrite and nitric oxide reductases were found soluble in extracts of Pseudomonas perfectomarinus cultured anaerobically at the expense of nitrate and ruptured with the French pressure cell. Malic enzyme, transhydrogenase, and flavin reductase that provided electron flow for these reductases were soluble as well. Nitrous oxide reductase remained particle-bound. Exogenous NADH was a poor electron donor for crude extracts, but a combination of malate, NADP, and NAD served well in the reduction of nitrite and nitric oxide. Nitrite reductase activity lost on dialysis of crude extract was restored by addition of this combination. Addition of free flavins was required for reduction of nitrite and nitric oxide. A nitrite reductase complex was separated from the nitric oxide reductase by gel filtration and DEAE-cellulose chromatography. NADH was an effective electron donor for this system with flavins provided as well. A c-type cytochrome with a split-α peak (perhaps associated with a d type) and two additional c...

Reduced nicotinamide-adenine dinucleotide-nitrite reductase from Azotobacter chroococcum

Abstract: 1. The assimilatory nitrite reductase of the N2-fixing bacterium Azotobacter chroococcum was prepared in a soluble form from cells grown aerobically with nitrate as the nitrogen source, and some of its properties have been studied. 2. The enzyme is a FAD-dependent metalloprotein (mol.wt. about 67000), which stoicheiometrically catalyses the direct reduction of nitrite to NH3 with NADH as the electron donor. 3. NADH–nitrite reductase can exist in two either active or inactive interconvertible forms. Inactivation in vitro can be achieved by preincubation with NADH. Nitrite can specifically protect the enzyme against this inactivation and reverse the process once it has occurred. 4. A. chroococcum nitrite reductase is an adaptive enzyme whose formation depends on the presence of either nitrate or nitrite in the nutrient solution. 5. Tungstate inhibits growth of the microorganism very efficiently, by competition with molybdate, when nitrate is the nitrogen source, but does not interfere when nitrite or NH3 is substituted for nitrate. The addition of tungstate to the culture media results in the loss of nitrate reductase activity but does not affect nitrite reductase.

Nitrite Reductase-deficient Mutants of Escherichia coli K12

Abstract: Summary: Mutants of Escherichia coli K12 have been isolated which reduce nitrite 3 to 30% as rapidly as the wild-type. Activities of reduced nicotinamide adenine dinucleotide (NADH)-nitrite oxidoreductase were lower in cell-free extracts of these nirA * mutants than in the wild-type. The mutants grew on minimal agar, and their sulphite reductase activity was the same as in the wild-type. Double mutants deficient in both nitrite and sulphite reductases were constructed, as well as recombinants which had regained one or both activities following recombination with Escherichia coli Hfr Hayes. The inability to reduce sulphite was due to an altered cysB† gene. Suspensions of nirA cysB + and nirA cysB bacteria reduced nitrite at similar rates, showing that sulphite reductase (which is a gratuitous nitrite reductase) contributes little to the rate of nitrite reduction in vivo. Cytochome c 552 was synthesized by nirA + cysB + double recombinants but not by nirA cysB or nirA cysB + bacteria. This data suggests that cytochrome c 552 is involved in nitrite reduction in E. coli either as a component of NADH-NO2 - oxidoreductase, or as an electron carrier whose synthesis is affected by the nir gene.

The appearance of nitrate reductase activity in nitrogen-starved cells of Ankistrodesmus braunii.

Abstract: Nitrate reductase activity was detectable in ammonium-grown cells of Ankistrodesmus braunii after 50 minutes of nitrogen starvation. The rate of formation of nitrate reductase was stimulated by addition of nitrate and inhibited completely by cycloheximide (20 μg/ml). Nitrogen-starved cells assimilated added nitrate or nitrite rapidly and no nitrite or nitrate was detectable in either cells or culture medium from cultures subjected to nitrogen starvation. It is concluded that nitrate is not obligatory for the formation of nitrate reductase.

Characteristics of Nitrate Reduction in a Mutant of the Blue-Green Alga Agmenellum quadruplicatum.

Abstract: Characteristics of nitrate reduction in terms of nitrite production in an N-methyl-N′-nitro-N-nitrosoguanidine-induced mutant of the blue-green alga Agmenellum quadruplicatum are described. Following induction of nitrate reduction a linear rate of nitrite production proportional to cell concentration was observed. Rate of nitrite production and growth rate showed similar responses to pH, temperature, and light intensity. If required, only trace amounts of carbon dioxide were necessary for nitrite production. Atmospheres of oxygen or nitrogen inhibited production of nitrite. In addition, a low but constant rate of nitrite production was observed in the dark. Nitrite production by mutant AQ-6 was studied in terms of photosynthesis. As nitrite production proceeded, rate of photosynthesis declined. Ultraviolet irradiation and 3-(3,4-dichlorophenyl)-1, 1-dimethylurea poisoning did not prevent nitrite production. The action spectrum of nitrite production was chlorophyll a-like.