Showing papers on "Nitrite published in 1980"

Nitrous Oxide from Soil Denitrification: Factors Controlling Its Biological Production

Abstract: Increasing concentrations of nitrate, nitrite, and molecular oxygen enhanced production of nitrous oxide relative to molecular nitrogen during denitrification in soils. Soil acidity interacted with nitrate to increase the ratio of nitrous oxide to molecular nitrogen. In response to anoxic conditions, nitrous oxide production initially increased but nitrous oxide was then consumed, a pattern which resulted from the sequential synthesis of nitrogenous oxide reductases.

Specific inhibition of nitrite oxidation by chlorate and its use in assessing nitrification in soils and sediments.

Abstract: A method was developed to determine the ammonium oxidation rate (potential) of unenriched natural samples by measuring the nitrite produced in shaken slurries. Addition of chlorate to the samples prevented nitrite from being oxidized to nitrate. The effectiveness and specificity of chlorate were tested with pure cultures of nitrite and ammonium oxidizers, as well as in soil and sediment slurries. It was concluded that chlorate had relatively little inhibitory effect on ammonium oxidation. However, under some conditions chlorate was not completely effective in blocking nitrite oxidation, and the causes of this were investigated. The technique was designed to check for incomplete blockage.

Nitrate and Nitrite Reduction

Abstract: Publisher Summary This chapter describes nitrate and nitrite reduction. Nitrate is the predominant form of nitrogen available to most cultivated plants grown under normal field conditions. Although ammoniacal fertilizers are used almost exclusively, the ammonia derived from these fertilizers is oxidized to nitrate by soil organisms. Nitrification is extremely rapid when the soil is well aerated, moist, and above 7°–10°C. Certain bacteria can utilize nitrate nitrogen as the sole nitrogen source for the synthesis of all nitrogen containing compounds of the cell. This nitrate assimilation can occur under both aerobic and anaerobic conditions. Nitrate reduction by partially purified enzyme preparations is frequently stimulated by phosphate. Nitrate reduction, mediated by either reduced pyridine nucleotides or reduced viologen dyes, is inhibited by cyanide and azide; however, pyridine-nucleotide-mediated reduction of cytochrome c is insensitive to these inhibitors. A reactivation of an inactive nitrate reductase apoenzyme extracted from molybdenum-deficient plants can be achieved by the addition of acid-treated nitrate reductase or by addition of phosphate buffer washes of nitrate reductase absorbed on adenosine monophosphate -Sepharose.

Production of nitrous oxide by ammonia-oxidizing chemoautotrophic microorganisms in soil.

Abstract: Gas chromatographic studies showed that nitrous oxide was produced in each instance when sterilized (autoclaved) soil was incubated after treatment with ammonium sulfate and inoculation with pure cultures of ammonia-oxidizing chemoautotrophic microorganisms (strains of Nitrosomonas, Nitrosospira, and Nitrosolobus). Production of N(2)O in ammonium-treated sterilized soil inoculated with Nitrosomonas europaea increased with the concentration of ammonium and the moisture content of the soil and was completely inhibited by both nitrapyrin and acetylene. Similar effects of nitrapyrin, acetylene, ammonium concentration, and soil moisture content were observed in studies of factors affecting N(2)O production in nonsterile soil treated with ammonium sulfate. These observations support the conclusion that, at least under some conditions, most of the N(2)O evolved from soils treated with ammonium or ammonium-producing fertilizers is generated by chemoautotrophic nitrifying microorganisms during oxidation of ammonium to nitrite.

The location of dissimilatory nitrite reductase and the control of dissimilatory nitrate reductase by oxygen in Paracoccus denitrificans.

Abstract: 1. A method is described for preparing spheroplasts from Paracoccus denitrificans that are substantially depleted of dissimilatory nitrate reductase (cytochrome cd) activity. Treatment of cells with lysozyme + EDTA together with a mild osmotic shock, followed by centrifugation, yielded a pellet of spheroplasts and a supernatant that contained d-type cytochrome. The spheroplasts were judged to have retained an intact plasma membrane on the basis that less than 1% of the activity of a cytoplasmic marker protein, malate dehydrogenase, was released from the spheroplasts. In addition to a low activity towards added nitrite, the suspension of spheroplasts accumulated the nitrite that was produced by respiratory chain-linked reduction of nitrate. It is concluded that nitrate reduction occurs at the periplasmic side of the plasma membrane irrespective of whether nitrite is generated by nitrate reduction or is added exogenously. 2. Further evidence for the integrity of the spheroplasts was that nitrate reduction was inhibited by O2, and that chlorate was reduced at a markedly lower rate than nitrate. These data are taken as evidence for an intact plasma membrane because it was shown that cells acquire the capability to reduce nitrate under aerobic conditions after addition of low amounts of Triton X-100 which, with the same titre, also overcame the permeability barrier to chlorate reduction by intact cells. The close relationship between the appearance of chlorate reduction and the loss of the inhibitory effect of O2 on nitrate reduction also suggests that the later feature of nitrate respiration is due to a control on the accessibility of nitrate to its reductase rather than on the flow of electrons to nitrate reductase.

Effects of temperature, ph, salinity, and inorganic nitrogen on the rate of ammonium oxidation by nitrifiers isolated from wetland environments.

Abstract: Ammonium-oxidizing bacteria were examined in two wetland environments, a freshwater marsh and an estuarine bay, during a 2-year period. Two predominant types were consistently isolated, one from each environment. Both isolates were identified as species ofNitrosomonas. Using a closed culture, high cell density assay, the effects of temperature, pH, salinity, Na(+), K(+), nitrite, nitrate, and ammonium concentrations on ammonium oxidation were determined. Maximum activity was observed for the freshwater isolate at 35°C, pH 8.5, salinities of 0.3 to 0.5% Na(+) and K(+), and ammonium concentrations greater than 0.5 g/l. For the estuarine isolate, maximum activity was observed at 40°C, pH 8.0, salinities of 0.5 to 1.0%, 1.0% Na(+) and K(+), and 0.2 g/l ammonium. The estuarine isolate had a Na(+) requirement which could be partially substituted by the K(+), suggesting that the organism is a true estuarine bacterium. Nitrite inhibited both isolates at concentrations greater than 5 mg/l, whereas nitrate had no significant effect on either isolate.

Nitrate and Nitrite in Saliva

Abstract: A survey is given on the occurrence of nitrate and nitrite in human saliva and the influence of the dietary nitrate intake. Nitrate, after its absorption in the upper gastrointestinal tract, reaches the salivary glands via the blood circulation where it is secreted into the oral cavity and partially reduced to nitrite by the oral microflora. There is a linear relationship between the amounts of nitrate ingested and amounts of nitrate and nitrite found in saliva. The ability of the oral microflora to reduce nitrate to nitrite depends on he individual ages. Mean salivary nitrite was found to increase from well below 1 ppm in infants of up to 6 months to about 7 ppm in adults. a remarkably different situation has been found in areas of high esophageal cancer incidence in Iran: although dietary intake of nitrate and nitrite is very low, nitrite levels in saliva, especially in children of this area tend to be much higher than those in children of western European countries.

Bacterial inhibitory effects of nitrite: inhibition of active transport, but not of group translocation, and of intracellular enzymes.

Abstract: Nitrite inhibited active transport of proline in Escherichia coli but not group translocation of sugar via the phosphoenolpyruvate:phosphotransferase system. These results were consistent with previous results that nitrite inhibits active transport, oxygen uptake, and oxidative phosphorylation in aerobic bacteria. Nitrite also inhibited aldolase (EC 4.1.2.13) from E. coli, Pseudomonas aeruginosa, Streptococcus faecalis, and rabbit muscle. Thus, these various data showed that nitrite has more than one site of attack in the bacterial cell. These data also indicated that nitrite is inhibitory to a wide range of physiological types of bacteria.

Nitric oxide in seawater.

Abstract: Nitrite photolysis at natural light intensities and normal nitrite concentrations in seawater produced detectable concentrations of nitric oxide, which was consumed rapidly by a dark chemical reaction in the laboratory. Nitric oxide was also detected in situ in nitrite-rich surface waters of the central equatorial Pacific, where it formed in daylight and disappeared rapidly at sunset. The formation and rapid cycling of nitric oxide implies the presence of other free radicals in seawater, perhaps as intermediates in ongoing autoxidation processes. The central equatorial Pacific is a nitric oxide source to the atmosphere.

N2O reduction by Vibrio succinogenes.

Abstract: Vibrio succinogenes grew anaerobically at the expense of formate oxidation, with nitrous oxide (N2O) serving a terminal oxidant. N2O was quantitatively reduced to dinitrogen (N2). In the presence of 5 x 10(-2) atm (ca. 5 kPa) of acetylene (C2H2), which inhibits the reduction of N2O, growth of V. succinogenes was completely inhibited. Nitrate was reduced to nitrite or to ammonia, depending on the extent of availability of formate, but N2 was not produced by reduction of nitrate. During the reduction of nitrate to ammonia, all eight electrons transported to a molecule of nitrate appeared to be coupled for energy-yielding reactions.

Denitrification of water using immobilized Pseudomonas denitrificans cells

Abstract: Preparations of living Pseudomonas denitrificans cells immobilized in alginate gel were used in the denitrification of water. In the presence of an exogenous carbon source the entrapped microorganisms reduced nitrate and nitrite to gaseous products and to achieve complete reduction, carbon to nitrogen ratios of over two were required. The effects on denitrification of particle size and the number of bacteria in the gel were investigated. Apparent Km values for nitrate and nitrite reduction were calculated for free and immobilized cells. When the immobilized cells were incubated in nutrient media, an increase in reduction rate was observed and this was shown to be caused by the growth of cells within the gel particles. Immobilized P. denitrificans cells retained 75% of their initial nitrate reduction capacity after 21 days of storage at +4°C. The operational stability of the alginate-immobilized cells was studied both in batch and in a column which was operated continuously. A column (45 g of alginate-cell fibers in 80 ml) denitrified a high nitrate drinking water (100 mg NO3/l) with a rate of 300 ml of nitrate and nitrite free water/day/g of gel. The half life for nitrate reduction was estimated to be 30 days.

Nitrite-Induced Methemoglobin Formation in Channel Catfish

Abstract: Nitrite that accumulates during intensive culture of channel catfish (Ictalurus punctatus) often results in high mortality. This study evaluated sublethal effects of nitrite on young channel catfish. Fish (7–10 cm standard length) exposed to 1, 2, 3, 4, or 5 mg/liter of nitrite for 24 hours developed mean methemoglobin concentrations (% of total hemoglobin) of 35, 79, 79, 85, and 90%, respectively. During the 5 mg/liter exposure, methemoglobin increased rapidly during the first 6 hours from 7% to 59%, more slowly to about 80% by 12 hours, and trivially thereafter. Channel catfish exposed to 5 mg/liter nitrite for 6 hours and transferred to nitrite-free water had near normal amounts of methemoglobin (13%) after 24 hours. An inverse relationship was noted between pH of aquarium water and methemoglobin formation after exposure to nitrite. Addition of calcium chloride, potassium chloride, sodium chloride, and sodium bicarbonate to the water suppressed methemoglobin formation in fish exposed to nitrit...

Daily dietary intakes of nitrate, nitrite and volative N-nitrosamines in the Netherlands using the duplicate portion sampling technique.

Abstract: In total, 201 duplicates of all foods and drinks sampled by adult volunteers during a 24-hour sampling period have been analyzed for nitrate, nitrite and volatile N-nitrosamines. For nitrate the mean daily intake was equivalent to 179 mg of potassium nitrate per 24 h, for nitrite this intake was equivalent to 4.2 mg of sodium nitrite per 24 h. The best estimate for the total daily fraction of salivary nitrite originating from dietary nitrate has been calculated as 6.3 mol%/24 h. For N-nitrosodimethylamine the mean daily intake was 0.38 microgram/24 h. The most important source of this nitrosamine contributing to the daily dietary intake was shown to be beer, which contributes 71% of the intake of an average consumer. Finally, attention has been drawn to the identification of N-nitroso-5-methyl-1,1-oxazolidine as an environmental nitrosamine present as an impurity in cutting fluids.

Formation of nitrous oxide and dinitrogen by chemical decomposition of hydroxylamine in soils

Abstract: Soil properties affecting formation of nitrous oxide (N2O) and dinitrogen (N2) by chemical decomposition of hydroxylamine (NH2OH) in soils were studied using 19 soils selected to obtain a wide range in properties. It was found that production of N2O by chemical decomposition of NH2OH in soils is more rapid than production of N2 and that, except with calcareous soils, N2O production greatly exceeds N2 production. Studies of the correlations between various soil properties and formation of N2O and N2 by decomposition of NH2OH showed that production of N2O was very highly correlated with exchangeable and oxidized Mn in the soils studied, and that production of N2 was very highly correlated with pH, CaCO3 equivalent, exchangeable Ca2+, and oxidized Mn. Production of N2 in neutral and acidic soils was highly correlated with both exchangeable and oxidized Mn, and production of N2 in calcareous soils was significantly correlated with oxidized Fe. The deductions from these correlations that Mn compounds are involved in the reactions leading to formation of N2O and N2 by chemical decomposition of NH2OH in soils, and that CaCO3 and Fe compounds are involved in the reactions leading to formation of N2 in calcareous soils, were supported by studies of N2O and N2 production through reactions of Mn and Fe compounds with NH2OH in the presence and absence of CaCO3. Production of N2O via chemical decomposition of NH2OH in soils greatly exceeds production of N2O through chemical decomposition of nitrite (i.e. via chemodenitrification), and the amount of N2 produced by decomposition of NH2OH in most soils exceeds the amount produced by decomposition of nitrite. Work reported indicates that, if N2O is formed in soils through nonbiological transformations of NH2OH produced by soil microorganisms, very little of this gas is generated by the reaction of NH2OH with nitrite frequently postulated as a mechanism of N2O production in soils (NH2OH + HNO2 → N2O + 2H2O).

Determination of nitrate and nitrite in meat products by using a nitrate ion-selective electrode

Abstract: A procedure for the determination of nitrate and nitrite in meat products by a direct potentiometric method with a nitrate ion-selective electrode is presented. The soluble nitrate and nitrite were extracted from the meat products with a Soxhlet extractor using borax buffer solution (pH 9). The effect of pH on the recovery of nitrite and nitrate was studied. Results obtained by the proposed method were compared with those obtained by recommended spectrophotometric methods. Storage of samples before analysis was also studied.

[23] Ferredoxin-nitrite reductase

Abstract: Publisher Summary This chapter describes ferredoxin-nitrite reductase. Ferredoxin-nitrite reductase (EC 1.7.7.1) is the second enzyme component of the photosynthetic nitrate-reducing system. It was first identified as a ferredoxin-dependent chloroplast enzyme which catalyzes the 6-electron reduction of nitrite to ammonia. Usual assay involves sodium dithionite as reductant and either ferredoxin or its artificial substitute, methyl viologen, as electron carrier. Enzymatic activity can be best followed by measuring colorimetrically the rate of disappearance of nitrite. The reaction is run in open test tubes. The reduced methyl viologen assay follows the nitrite reductase activity of a purified preparation by measuring colorimetrically at 604 nm the rate of nitrite-dependent oxidation of reduced methyl viologen (MVH), which can be prepared with H 2 and platinum asbestos. The NADPH assay method is based on the use of NADPH and ferredoxin–NADP reductase as electron-donor system to reduce ferredoxin. It follows nitrite reductase activity by measuring colorimetrically the rate of disappearance of nitrite. Nitrite reductases from spinach, calabash, Curcubita pepo, and Chlorella have been purified to homogeneity. The purified enzyme can be stored in the deep-freeze for several months with no loss in activity.

The Exposure of Humans to Nitrite

Abstract: Although nitrate is more abundant than nitrite in food and the environment in general, it requires reduction by, for instance, bacterial or plant enzymes before it is involved in the nitrosation of amines or amides. Part of the exposure of humans to nitrite arises from its use as a food additive where it performs a very useful function in protecting the consumer from pathogenic micro-organisms such as Clostridium botulinum. Some untreated foodstuffs, such as potatoes, tomatoes and beets, also contain low levels of nitrite. Nevertheless, the main source of human contact is that produced in vivo from nitrate ingested in foods in general and in vegetables in particular. Nitrate also occurs widely in drinking water supplies and this source can also contribute in some measure to human exposure. As yet, it is not possible to compute with accuracy the contribution from any endogenous synthesis within the gastrointestinal tract. Since the rate of nitrosation of an amine is dependent on the nitrite concentration to a power of greater than unity, it is probable that nitrite ingested in one application over a short period will be more active in the synthesis of N-nitroso compounds than a continuous supply at lower concentrations over long periods.

Role of nitrite in cured meat flavor: antioxidant role of nitrite

Abstract: The antioxidant activity of nitrite was investigated in model systems containing linoleic acid, Tween 20, and phosphate buffer. Results indicated that nitrite by itself can act as a prooxidant especially at concentrations greater than 25 mg/kg (parts per million). However, the addition of nitrite to model systems containing prooxidants such as Fe++ or Fe++-EDTA substantially reduced the rates of oxidation. Lipid oxidation catalyzed by aqueous beef extract also showed a marked decrease upon the addition of nitrite. Nitrite also produced a significant effect (p < 0.05) on heme-catalyzed lipid oxidation although the nature of this effect was not established. Further studies with an aqueous extract of pork demonstrated that dialysis removes a fraction which is largely responsible for the catalytic effect of meat extracts on lipid oxidation. Trace metal analysis revealed the presence of iron in the dialyzates from these extracts. Nitrite may function as a metal chelator to tie up these trace metals present in meat.

A Nitrate Reductase-less Variant Isolated from Suspension Cultures of Datura innoxia (Mill.).

Abstract: A comparative study has been carried out of the growth of two lines of Datura innoxia (Mill.) cells, designated DI-6 and NR1, their resistance to chlorate, and their ability to assimilate nitrate in sterile culture. The NR1 cell line was isolated from DI-6 cultures by first growing the latter in a nitrate-based medium for 5 days and then transferring the cells to a medium containing 2 grams liter −1 of casein hydrolysate as the sole N source and 49 millimolar KClO 3 for a 6-week incubation period. Cells which survived the chlorate treatment then were transferred to casein hydrolysate medium and have been cultured in the absence of chlorate for more than 18 months (NR1). DI-6 cells can grow in a nitrate-based medium, whereas NR1 cells can take up nitrate but cannot use it as a N source. The inability of NR1 to assimilate nitrate appears to be due to the lack of an active nitrate reductase in these cells. Through the use of a variety of electron donors and acceptors, the lack of nitrate reductase activity in NR1 cells was shown to be due to the absence of, or a defect in, that component of the enzyme which mediates the reduction of nitrate to nitrite. In other experiments, DI-6 and NR1 were grown on a solid medium containing casein hydrolysate (2 grams liter −1 ) as the sole N source. Under these culture conditions, neither cell line contained an active nitrate reductase. The growth on this medium was compared to that on the same medium containing chlorate at concentrations from 0 to 100 millimolar. DI-6 culture growth was inhibited by 70% at a chlorate concentration of 30 micromolar, whereas growth of NR1 was stimulated by more than 60% on the same medium and by 100% at a chlorate concentration of 30 millimolar. In the presence of 100 millimolar chlorate, the growth of both cell lines was completely inhibited. This clear difference between the response of DI-6 and NR1 cells to chlorate even in the absence of nitrate lends support to the observations by others that chlorate inhibits cells by a mechanism other than, or in addition to, its nitrate reductase-catalyzed conversion to chlorite. Nitrite reductase was induced by nitrate in NR1 cells as well as in DI-6. This observation is a further confirmation of the fact that nitrate, not nitrite, is the true inducer of the nitrate assimilatory pathway in higher plants.