Showing papers on "Nitrite published in 2001"

Nitrite‐derived nitric oxide: a possible mediator of ‘acidic–metabolic’ vasodilation

Abstract: The fundamental, yet poorly understood, physiological mechanism known as 'acidic-metabolic' vasodilation, contributes to local blood flow regulation during hypoxia/ischaemia and increased metabolic activity. The vasodilator nitric oxide (NO) has been suggested to be involved in this event. Besides enzymatic production by NO synthases, a novel mechanism for generation of this gas in vivo was recently described. This involves non-enzymatic reduction of inorganic nitrite to NO, a reaction that takes place predominantly during acidic/reducing conditions. We have studied the effects of physiological amounts of nitrite on NO generation and relaxation of rat aorta in vitro in a situation where environmental pH was reduced to levels seen in tissues during hypoxia/ischaemia. The relaxatory effect of nitrite was increased in an acidic buffer solution (pH 6.6) compared with neutral pH; EC50 for nitrite was reduced from 200 to 40 microM. Nitrite-evoked relaxation was effectively prevented by coadministration of an inhibitor of soluble guanylyl cyclase. The relaxation was further potentiated by the addition of ascorbic acid. In parallel, NO was generated from nitrite in a pH dependent manner with even larger amounts seen after addition of ascorbic acid. NO generation from nitrite correlated to the the degree of relaxation of rat aorta. These results illustrate non-enzymatic release of NO from nitrite at physiological concentrations. This may be an important auto-regulated physiological mechanism involved in the regulation of vascular tone during hypoxia/ischaemia.

A plasma membrane-bound enzyme of tobacco roots catalyses the formation of nitric oxide from nitrite.

Abstract: Purified plasma membranes (PMs) of tobacco (Nicotiana tabacum L. cv. Samsun) roots exhibited a nitrite-reducing enzyme activity that resulted in nitric oxide (NO) formation. This enzyme activity was not detected in soluble protein fractions or in PM vesicles of leaves. At the pH optimum of pH 6.0, nitrite was reduced to NO with reduced cytochrome c as electron donor at a rate comparable to the nitrate-reducing activity of root-specific succinate-dependent PM-bound nitrate reductase (PM-NR). The hitherto unknown PM-bound nitrite: NO-reductase (NI-NOR) was insensitive to cyanide and anti-NR IgG and thereby proven to be different from PM-NR. Furthermore, PM-NR and NI-NOR were separated by gel-filtration chromatography and apparent molecular masses of 310 kDa for NI-NOR and 200 kDa for PM-NR were estimated. The PM-associated NI-NOR may reduce the apoplastic nitrite produced by PM-NR in vivo and may play a role in nitrate signalling via NO formation.

Optimal operational factors for nitrite accumulation in batch reactors.

Abstract: The environmental factors that affected the accumulation of nitrite in nitrifying reactors were investigated using a mixed culture A batch reactor with 50 mg-N/l of ammonia was used The pH, temperature and dissolved oxygen concentration were varied The concentration of unionized free ammonia also changed with the oxidation of ammonia and the variation of pH and temperature The accumulation of nitrite was affected sensitively by pH and temperature A higher nitrite concentration was observed at pH 8-9 or temperature around 30 °C The dissolved oxygen also affected, giving the highest nitrite accumulation at around 15 mg/l These were the favoredconditions for nitrite production The free ammonia concentration influenced thenitrite accumulation also, by inhibiting nitrite oxidation The inhibition becameapparent at a concentration of approximately 4 mg/l or above, but insignificant atbelow 1 mg/l Thus, simultaneously high free ammonia concentration and maximumspecific ammonia-oxidation rate (above 15 × 10-3 mg-N/mg-VSSċh)were needed for a significant nitrite accumulation When the two conditions were met, thenthe highest accumulation was observed when the ratio of the maximum specific oxidationrate of ammonia to the maximum specific oxidation rate of nitrite (ka/kn) was highestUnder the optimal operating conditions of pH 8, 30 °C and 15 mg/l of dissolvedoxygen, as much as 77% of the removed ammonia accumulated in nitrite

Peptide methionine sulfoxide reductase from Escherichia coli and Mycobacterium tuberculosis protects bacteria against oxidative damage from reactive nitrogen intermediates.

Abstract: Inducible nitric oxide synthase (iNOS) plays an important role in host defense. Macrophages expressing iNOS release the reactive nitrogen intermediates (RNI) nitrite and S-nitrosoglutathione (GSNO), which are bactericidal in vitro at a pH characteristic of the phagosome of activated macrophages. We sought to characterize the active intrabacterial forms of these RNI and their molecular targets. Peptide methionine sulfoxide reductase (MsrA; EC 1.8.4.6) catalyzes the reduction of methionine sulfoxide (Met-O) in proteins to methionine (Met). E. coli lacking MsrA were hypersensitive to killing not only by hydrogen peroxide, but also by nitrite and GSNO. The wild-type phenotype was restored by transformation with plasmids encoding msrA from E. coli or M. tuberculosis, but not by an enzymatically inactive mutant msrA, indicating that Met oxidation was involved in the death of these cells. It seemed paradoxical that nitrite and GSNO kill bacteria by oxidizing Met residues when these RNI cannot themselves oxidize Met. However, under anaerobic conditions, neither nitrite nor GSNO was bactericidal. Nitrite and GSNO can both give rise to NO, which may react with superoxide produced by bacteria during aerobic metabolism, forming peroxynitrite, a known oxidant of Met to Met-O. Thus, the findings are consistent with the hypotheses that nitrite and GSNO kill E. coli by intracellular conversion to peroxynitrite, that intracellular Met residues in proteins constitute a critical target for peroxynitrite, and that MsrA can be essential for the repair of peroxynitrite-mediated intracellular damage.

Nitrification at low oxygen concentration in biofilm reactor

Abstract: A nitrification process under low dissolved oxygen (DO) concentration is proposed in a completely stirred biofilm reactor. The reactor was fed with a synthetic wastewater containing 250 mg NH\d4–N/L. A stable nitrite accumulation in the effluent was obtained during >110 days’ operation; NO\d2–N(NO\d2–N+NO\d3–N) in the effluent reached >90% under 0.5 mg DO/L. Ammonium was completely converted and NH\d4–N in the outlet was as low as 5 mg/L. A transient increase of the DO concentration in the reactor induced a complete conversion of ammonia and nitrite to nitrate after only 2 days. A return to a low DO concentration again induced nitrite accumulation. These results show that the nitrite oxidizers were always present in the reactor but were outcompeted at low DO concentration, due to their lower affinity for oxygen, compared with ammonia oxidizers. Nitrite accumulation could also be favored by free nitrous acid accumulation inside the biofilm.

Rapid abiotic transformation of nitrate in an acid forest soil

Abstract: Nitrate immobilization into organic matter is thought to require catalysis by the enzymes of soil microorganisms. However, recent studies suggest that nitrate added to soil is immobilized rapidly and this process may include abiotic pathways. We amended living and sterilized soil with 15 N-labeled nitrate and nitrite to investigate biotic and abiotic immobiliz- ation. We report rapid transformation of nitrate in incubations of the O layer of forest soils that have been sterilized to prevent microbial activity and to denature microbial enzymes. Approximately 30, 40, and 60% of the 15 N-labeled nitrate added to live, irradiated, or auto- claved organic horizon soil disappeared from the extractable inorganic-N pool in less than 15 minutes. About 5% or less of the nitrate was recovered as insoluble organic N in live and sterilized soil, and the remainder was determined to be soluble organic N. Added 15 N- nitrite, however, was either lost to gaseous N or incorporated into an insoluble organic N form in both live and sterile organic soils. Hence, the fate and pathway of apparent abiotic nitrate immobilization differs from the better-known mechanisms of nitrite reactions with soil organic matter. Nitrate and nitrite added to live A-horizon soil was largely recovered in the form added, suggesting that rapid conversion of nitrate to soluble organic-N may be limited to C-rich organic horizons. The processes by which this temperate forest soil transforms added nitrate to soluble organic-N cannot be explained by established mechanisms, but appears to be due to abiotic processes in the organic horizon.

Dissimilatory Nitrite Reductase Genes from Autotrophic Ammonia-Oxidizing Bacteria

Abstract: The presence of a copper-containing dissimilatory nitrite reductase gene (nirK) was discovered in several isolates of β-subdivision ammonia-oxidizing bacteria using PCR and DNA sequencing. PCR primers Cunir3 and Cunir4 were designed based on published nirK sequences from denitrifying bacteria and used to amplify a 540-bp fragment of the nirK gene from Nitrosomonas marina and five additional isolates of ammonia-oxidizing bacteria. Amplification products of the expected size were cloned and sequenced. Alignment of the nucleic acid and deduced amino acid (AA) sequences shows significant similarity (62 to 75% DNA, 58 to 76% AA) between nitrite reductases present in these nitrifiers and the copper-containing nitrite reductase found in classic heterotrophic denitrifiers. While the presence of a nitrite reductase in Nitrosomonas europaea is known from early biochemical work, preliminary sequence data from its genome indicate a rather low similarity to the denitrifier nirKs. Phylogenetic analysis of the partial nitrifier nirK sequences indicates that the topology of the nirK tree corresponds to the 16S rRNA and amoA trees. While the role of nitrite reduction in the metabolism of nitrifying bacteria is still uncertain, these data show that the nirK gene is present in closely related nitrifying isolates from many oceanographic regions and suggest that nirK sequences retrieved from the environment may include sequences from ammonia-oxidizing bacteria.

Nitrate and nitrite transport in bacteria

Abstract: The topological arrangements of nitrate and nitrite reductases in bacteria necessitate the synthesis of transporter proteins that carry the nitrogen oxyanions across the cytoplasmic membrane. For assimilation of nitrate (and nitrite) there are two types of uptake system known: ABC transporters that are driven by ATP hydrolysis, and secondary transporters reliant on a proton motive force. Proteins homologous to the latter type of transporter are also involved in nitrate and nitrite transport in dissimilatory processes such as denitrification. These proteins belong to the NarK family, which is a branch of the Major Facilitator Superfamily. The mechanism and substrate specificity of transport via these proteins is unknown, but is discussed in the light of sequence analysis of members of the NarK family. A hypothesis for nitrate and nitrite transport is proposed based on the finding that there are two distinct types of NarK.

Increased nitric oxide metabolites in exhaled breath condensate after exposure to tobacco smoke

Abstract: BACKGROUND Cigarette smoking reduces the level of exhaled nitric oxide (NO) in healthy subjects, although the mechanism is unclear. NO is a highly reactive molecule which can be oxidised or complexed with other biomolecules, depending on the microenvironment. The stable oxidation end products of NO metabolism are nitrite and nitrate. This study investigated the effect of smoking on NO metabolites in exhaled breath condensate. METHODS Fifteen healthy current smokers were recruited together with 14 healthy non-smokers. Measurement of exhaled NO, lung function, and collection of exhaled breath condensate were performed. Nitrite, nitrite + nitrate, S-nitrosothiols, and nitrotyrosine levels were measured. The effect of inhaling two cigarettes in smokers was also evaluated. The mean level of exhaled NO in smokers was significantly lower than in non-smokers (4.3 (0.3) ppb v 5.5 (0.5) ppb, p RESULTS There was no difference in the levels of nitrite, nitrite + nitrate, S-nitrosothiols, and nitrotyrosine in the exhaled breath condensate at the baseline visit between smokers and non-smokers. After smoking, nitrite + nitrate levels were significantly but transiently increased (from 20.2 (2.8) μM to 29.8 (3.4) μM, p CONCLUSIONS These findings suggest that acute smoking can increase the level of nitrate, but not nitrite, S-nitrosothiols, or nitrotyrosine in breath condensate. The deleterious effect of oxidant radicals induced by smoking may contribute to the epithelial damage of airways seen in smokers.

Antimicrobial effect of acidified nitrite on dermatophyte fungi, Candida and bacterial skin pathogens

Abstract: Aims: Nitric oxide is generated from sweat nitrite in the acidic environment of the skin surface and is thought to contribute to protection against infection. This study examined the sensitivity of Trichophyton mentagrophytes, T. rubrum, Candida albicans, Streptococcus pyogenes, Staphylococcus aureus and Propionibacterium acnes to acidified nitrite. Methods and Results: Organisms were cultured in varying concentrations of nitrite and pH for different lengths of time, before being transferred to recovery medium. With the exception of Strep. pyogenes, addition of nitrite increased the antimicrobial activity of acid solutions against all organisms tested. The rank order of sensitivity was: C. albicans < T. rubrum < T. mentagrophytes < Staph. aureus < P. acnes, with P. acnes being most sensitive. Conclusions: This work has shown that acidified nitrite is microbiocidal to common cutaneous pathogens. The concentrations of nitrite required to kill pathogenic fungi and bacteria in in vitro assays were higher than the concentrations of nitrite measured in sweat. However, additional co-factors in vivo and in sweat may potentiate the effect of acidified nitrite. Significance and Impact of the Study: Pharmacological preparations of acidified nitrite are novel antimicrobial agents. These data suggest skin organisms which may be sensitive to this treatment.

Control of biogenic H(2)S production with nitrite and molybdate.

Abstract: The effects of the metabolic inhibitors, sodium nitrite and ammonium molybdate, on production of H2S by a pure culture of the sulfate-reducing bacterium (SRB) Desulfovibrio sp. strain Lac6 and a consortium of SRB, enriched from produced water of a Canadian oil field, were investigated. Addition of 0.1 mM nitrite or 0.024 mM molybdate at the start of growth prevented the production of H2S by strain Lac6. With exponentially growing cultures, higher levels of inhibitors, 0.25 mM nitrite or 0.095 mM molybdate, were required to suppress the production of H2S. Simultaneous addition of nitrite and molybdate had a synergistic effect: at time 0, 0.05 mM nitrite and 0.01 mM molybdate, whereas during the exponential phase, 0.1 mM nitrite and 0.047 mM molybdate were sufficient to stop H2S production. With an exponentially growing consortium of SRB, enriched from produced water of the Coleville oil field, much higher levels of inhibitors, 4 mM nitrite or 0.47 mM molybdate, were needed to stop the production of H2S. The addition of these inhibitors had no effect on the composition of the microbial community, as shown by reverse sample genome probing. The results indicate that the efficiency of inhibitors in containment of SRB depends on the composition and metabolic state of the microbial community. Journal of Industrial Microbiology & Biotechnology (2001) 26, 350–355.

Nitric Oxide Signaling and Transcriptional Control of Denitrification Genes in Pseudomonas stutzeri

Abstract: The expression of denitrification by a facultatively anaerobic bacterium requires as exogenous signals a low oxygen tension concomitant with an N oxide. We have studied the role of nitric oxide (NO), nitrous oxide (N2O), and nitrite as signal molecules for the expression of the denitrification apparatus of Pseudomonas stutzeri. Transcriptional kinetics of structural genes were monitored by Northern blot analysis in a 60-min time frame after cells were exposed to an N oxide signal. To differentiate the inducer role of NO from that of nitrite, mRNA kinetics were monitored under anoxic conditions in a nirF strain, where NO generation from nitrite is prevented because of a defect in heme D1 biosynthesis. NO-triggered responses were monitored from the nirSTB operon (encoding cytochrome cd1 nitrite reductase), the norCB operon (encoding NO reductase), nosZ (encoding nitrous oxide reductase), and nosR (encoding a putative regulator). Transcription of nirSTB and norCB was activated by 5 to 50 nM NO, whereas the nosZ promoter required about 250 nM. Nitrite at 5 to 50 nM elicited no response. At a threshold concentration of 650 nM N2O, we observed in the anoxic cell the transient appearance of nosZ and nosR transcripts. Constant levels of transcripts of both genes were observed in an anoxic cell sparged with N2O. NO at 250 nM stimulated in this cell type the expression of nos genes severalfold. The transcription factor DnrD, a member of the FNR-CRP family, was found to be part of the NO-triggered signal transduction pathway. However, overexpression of dnrD in an engineered strain did not result in NirS synthesis, indicating a need for activation of DnrD. NO modified the transcriptional pattern of the dnrD operon by inducing the transcription of dnrN and dnrO, located upstream of dnrD. Insertional mutagenesis of dnrN altered the kinetic response of the nirSTB operon towards nitrite. Our data establish NO and DnrD as key elements in the regulatory network of denitrification in P. stutzeri. The NO response adds to the previously identified nitrate-nitrite response mediated by the NarXL two-component system for the expression of respiratory nitrate reductase encoded by the narGHJI operon.

Nitrate Reduction and signalling

Abstract: The ability to use nitrate as sole nitrogen source to sustain growth is a property shared by some bacteria and fungi and by most algae and plants. The biochemical pathway responsible for nitrate assimilation seems to be the same in both prokaryotes and eukaryotes. Soil nitrate is the preferred inorganic nitrogen source for many wild or cultivated plants. It seems, indeed, that most plants, unlike bacteria or fungi, which preferentially use ammonium as a nitrogen source, show better growth when nitrate is present. The generalisation of the use of chemical fertilizers has allowed a tremendous increase in crop yield during the past 50 years. However, there is now a growing concern about the effect of nitrate, on both the environment and human health (Chap. 8). Indeed, nitrate can accumulate in high concentrations in the leaves of edible plants or in drinking water. Once taken up from the soil by an active process (see Chap. 1.1), nitrate is either stored in the plant root system or translocated to aerial parts via the xylem. High concentrations of nitrate can be found in vacuoles and it seems that nitrate, beside its role as a nutrient, participates in the maintenance of the plant osmoticum. The first committed step of the nitrate assimilation pathway is the reduction of nitrate to nitrite, catalysed by assimilatory nitrate reductase (NR, Fig. 1). In some bacteria, dissimilatory nitrate reduction, in which nitrate replaces oxygen as a terminal electron acceptor for respiration, is also found, but the utilisation of nitrate for respiration in anaerobic plant cells is still debated. The nitrite formed by NR activity is translocated to the chloroplast, where it is further reduced to ammonium by nitrite reductase (NiR). Ammonium is subsequently incorporated into the amino acid pool through the action of glutamine synthetase (GS) and glutamate synthase (GOGAT) (see Chap. 2.2 and Fig. 1).

New spectrophotometric method for the determination of nitrite in water

Abstract: A selective and rapid spectrophotometric method for the determination of nitrite is presented. It relies on the reaction of nitrite with p-aminoacetophenone to form a diazonium ion, which is coupled with citrazinic acid in a basic medium to form an azo dye, which shows an absorption maximum at 495 nm. The colour is stable for 3h. Beer's law is obeyed in the range of 0.5 to 12 mug of nitrite in a final volume of 10 ml, with a molar absorptivity and its Sandell's sensitivity are 2.9 x 10(4) l mol(-1) cm(-1) and 16 ng cm(-2), respectively. The optimum reaction conditions and other analytical parameters are evaluated. The method has been successfully applied to the determination of nitrite in natural waters.

Antimicrobial effect of acidified nitrite on periodontal bacteria.

Abstract: The antimicrobial agent nitric oxide (NO) is formed in the mouth and its concentration is directly related to salivary nitrite, which in turn is related to dietary nitrate intake. The aim of this study was to determine whether nitrite under acidic conditions will have an inhibitory effect, possibly occurring through NO production, on the periodontal disease pathogens Fusobacterium nucleatum, Eikenella corrodens and Porphyromonas gingivalis. Whereas the growth of these organisms was inhibited by a more acid pH, the addition of nitrite caused a marked, further dose-dependent reduction in bacterial numbers after exposure. The ability of these bacteria to recover from nitrite exposure was also affected by pH and nitrite concentration. At acidity levels below pH 5.0, low concentrations of nitrite (0.2 mM) caused effective complete killing of the periodontal bacteria. Addition of sodium thiocyanate did not increase the bacteriostatic or bacteriocidal activity of acidified nitrite against any of the 3 bacteria. These results demonstrate the possibility that nitrite in saliva, under appropriate conditions, may have an effect on the growth and survival of the bacteria implicated in periodontal disease.

The promoting role of noble metals on NOx storage catalyst and mechanistic study of NOx storage under lean-burn conditions

Abstract: The promoting roles of noble metals (Pt, Rh, and Pd) and NOx storage mechanism were investigated on alkaline earth metal oxide-based NOx storage catalysts under lean-burn conditions. It was found that noble metals increased the reaction rates of NO oxidation to NO2 and nitrite oxidation to nitrate, resulting in an increase of NOx adsorption and nitrate formation. The rates of NO oxidation to NO2, nitrite oxidation to nitrate, and NOx adsorption were found to increase in the order of CaO/Al2O3 < Pd/CaO/Al2O3 < Pt/CaO/Al2O3 < Rh/CaO/Al2O3. In situ FTIR spectra showed that adsorbed NO2, nitrite (NO2-), and nitrate (NO3-) were formed after the noble metal-doped CaO/Al2O3 catalysts were treated by NOx (+O2) at 300 °C. But the adsorbed NO2 and nitrite species were found to vanish with the formation of strong surface nitrate species. It was proposed that nitrite and NO2 adspecies acted as intermediates and nitrate mainly came from oxidation of nitrite. NOx stored on the catalysts was present mainly as nitrate. I...