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PubMed1993

Mutagenicity of iso-butyl nitrite vapor in the Ames test and some relevant chemical properties, including the reaction of iso-butyl nitrite with phosphate.

We examined the mutagenicity of iso-butyl nitrite (IBN) vapor and aqueous IBN solution in the Ames test to help evaluate the hazard of sniffing this vapor, a habit which might play a role in the induction of Kaposi's sarcoma associated with acquired immune deficiency syndrome. Chemical analysis showed that the saturated vapor contained 190 micrograms IBN/ml at 25 degrees C, and saturated aqueous solution, 2.6 mg IBN/ml at 21-23 degrees C. When agar plates containing Salmonella typhimurium TA-1535 and rat liver S-9 were exposed to IBN vapor, the number of mutants reached a maximum after 40 min. A mean of 307 mutants/plate (22 x background) was observed when the plates were exposed to IBN vapor for 30 min. Addition of 0.2 ml saturated IBN solution in water to similar plates gave a mean of 179 mutants/plate (7.9 x background) in the absence of S-9, confirming published results. The S-9 did not affect the results. Based on the IBN level in medium exposed to IBN vapor, the vapor was apparently 11 times more mutagenic than IBN solution. This was attributed to continuous replenishment of unstable IBN in the medium by the vapor. The half-life of IBN at 21-23 degrees C was > 1 hr for solutions in water and < 3 min for solutions in the assay medium. This instability was traced to a reaction with phosphate, presumably hydrolysis to nitrite and iso-butanol. IBN in solution was 2.8 times more mutagenic than sodium nitrite, suggesting that IBN was not mutagenic because of its conversion to nitrite. Iso-butanol was not mutagenic. The results demonstrate the potential hazard of sniffing IBN vapor.

Aerosols↗

PubMed1998

Application of nitrite reductase from Alcaligenes faecalis S-6 for nitrite measurement.

The enzymatic reaction of nitrite reductase (NIR) from Alcaligenes faecalis S-6 was applied to the measurement of nitrite. NIR was immobilized on the surface of a gold electrode using filter paper and a dialysis membrane, and used as a working electrode in a three-electrode system. Amperometric methods were applied using NIR and the electron mediator 1-methoxy PMS (1-methoxy-5-methylphenazinium methylsulfate). The decrease in cathodic current showed a correlation to nitrite concentration over the range 0-1 mg/l. Measurements using a batch-flow type system gave a lower detection limit of 0.01 mg/l. This is sufficient for the detection of nitrite in natural waters.

Alcaligenes↗

PubMed1994

X-ray structure and site-directed mutagenesis of a nitrite reductase from Alcaligenes faecalis S-6: roles of two copper atoms in nitrite reduction.

Nitrite reductase (NIR) from the denitrifying bacterium Alcaligenes faecalis S-6 is a copper-containing enzyme which requires pseudoazurin, a low molecular weight protein containing a single type I copper atom, as a direct electron donor in vivo. Crystallographic analysis shows that NIR is a trimer composed of three identical subunits, each of which contains one atom of type I copper and one atom of type II copper, and that the ligands to the type I and type II copper atoms are the same as those of the Achromobacter cycloclastes NIR. An efficient NIR expression-secretion system in Escherichia coli was constructed and used for site-directed mutagenesis. An NIR mutant with a replacement of the type II copper ligand, His135, by Lys still retained a type II copper site as well as a type I copper atom, but it completely lost nitrite-reducing activity as measured with methyl viologen as an electron donor. On the other hand, another mutant with a replacement of the type I copper ligand, Met150, by Glu contained only a type II copper atom, but it still retained significant nitrite-reducing activity with methyl viologen. When pseudoazurin was used as an electron donor for the reaction, however, Met150Glu failed to catalyze the reduction of nitrite. Kinetic analysis of the electron transfer between NIR and pseudoazurin revealed that the electron-transfer rate between Met150Glu and pseudoazurin was reduced 1000-fold relative to that of wild-type NIR.(ABSTRACT TRUNCATED AT 250 WORDS)

Alcaligenes↗

PubMed1999

Kinetics of nirS expression (cytochrome cd1 nitrite reductase) in Pseudomonas stutzeri during the transition from aerobic respiration to denitrification: evidence for a denitrification-specific nitrate- and nitrite-responsive regulatory system.

After shifting an oxygen-respiring culture of Pseudomonas stutzeri to nitrate or nitrite respiration, we directly monitored the expression of the nirS gene by mRNA analysis. nirS encodes the 62-kDa subunit of the homodimeric cytochrome cd1 nitrite reductase involved in denitrification. Information was sought about the requirements for gene activation, potential regulators of such activation, and signal transduction pathways triggered by the alternative respiratory substrates. We found that nirS, together with nirT and nirB (which encode tetra- and diheme cytochromes, respectively), is part of a 3.4-kb operon. In addition, we found a 2-kb monocistronic transcript. The half-life of each of these messages was approximately 13 min in denitrifying cells with a doubling time of around 2.5 h. When the culture was subjected to a low oxygen tension, we observed a transient expression of nirS lasting for about 30 min. The continued transcription of the nirS operon required the presence of nitrate or nitrite. This anaerobically manifested N-oxide response was maintained in nitrate sensor (NarX) and response regulator (NarL) knockout strains. Similar mRNA stability and transition kinetics were observed for the norCB operon, encoding the NO reductase complex, and the nosZ gene, encoding nitrous oxide reductase. Our results suggest that a nitrate- and nitrite-responsive regulatory circuit independent of NarXL is necessary for the activation of denitrification genes.

Aerobiosis↗

PubMed1994

Nitrite-induced mutations in a forward mutation assay: influence of nitrite concentration and pH.

The mutagenicity of sodium nitrite at three pHs (7.4, 6.4 and 5.4) has been investigated by treating a shuttle vector plasmid in vitro and assaying for mutations within the supF target gene following replication of the damaged plasmid in human Ad293 cells. Mutation frequency increased with increasing nitrite concentration and decreasing pH. Among treatments from which a significant number of mutants could be collected, the most commonly induced mutations were GC-->AT transitions (44-56% of total mutations), followed by GC-->TA transversions (24-30%). The types of mutations induced at different nitrite concentrations and different pH's were similar, though some differences in their distribution throughout the supF gene were noted. These results provide information on the types of mutations that may be produced following the processing of nitrite-induced DNA damage in human cells.

Base Sequence↗

PubMed2004

Effects of seawater salinity on nitrite accumulation in short-range nitrification to nitrite as end product.

The effect of seawater salinity on nitrite accumulation in short-range nitrification to nitrite as the end product was studied by using a SBR. Experimental results indicated that the growth of nitrobacteria was inhibited and very high levels of nitrite accumulation at different salinities were achieved under the conditions of 25-28 degrees C, pH 7.5-8.0, and the influent ammonia nitrogen of 40-70 mg/L when seawater flow used to flush toilet was less than 35% (salinity 12393 mg/L, Cl- 6778 mg/L) of total domestic wastewater flow, which is mainly ascribed to much high chlorine concentration of seawater. Results showed that high seawater salinity is available for short-range nitrification to nitrite as the end product. When the seawater flow used to flush toilet accounting for above 70% of the total domestic wastewater flow, the removal efficiency of ammonia was still above 80% despite the removal of organics declined obviously (less than 60%). It was found that the effect of seawater salinity on the removal of organics was negative rather than positive one as shown for ammonia removal.

Ammonia↗

PubMed1990

[Nitrates and nitrites and the utilization of beta-carotene. I. The effect of different amounts of dietary nitrates and nitrites on the utilization of beta-carotene in rats].

The subject of the study was demonstration whether and in what extent different amounts of nitrates and nitrites in the diet affect the utilization of beta-carotene by rat organism. The level of vitamin A in the liver was accepted as an indicator of this utilization in accordance with the method of combined balance studies and liver test; additionally the plasma vitamin A level was determined. Two biological experiments lasting 30 days were carried out on male Wistar rats standardized with respect to hepatic vitamin A content. The animals were given orally 30 mcg daily an oil solution of beta-carotene and diets with varying amounts of potassium nitrate (0.5; 1.0; 2.0; 4.0; 6.0%) and sodium nitrite (0.05; 0.1; 0.5; 1.0%). Nitrates and nitrites in the diets reduced the utilization of beta-carotene in a dose-dependent way. The nitrate reduced the utilization of the provitamins by from about 50% to over 60%, and the nitrite reduced it by from over 60% to about 80%. The studied compounds exerted also a negative effect on the consumption of diet and weight gain.

Animals↗

PubMed1987

[Dynamics of endogenous bacterial nitrite formation in the stomach. 3. Dependence of nitrate and nitrite concentration on secretion volume].

The nitrate and nitrite concentration of 96 fasting gastric juice samples of young healthy volunteers were analysed. Two different methods have been used to take the gastric juice: 54 secrete samples were taken directly from the stomach, 42 secrete samples were taken after instillation of 500 ml sterile nitrite and nitrate free NaCl solution ("gastric-washing"). It could be shown that the expected high dilution of nitrite and nitrate concentration after gastric washing does not occur. A possible explanation might be that the solubilisation we could formerly observe in a biological pattern leads to a release of ions. This fact is very important for the question of endogen synthesis of cancerogenic N-nitroso compounds, because high nitrite and nitrate concentrations are subjects of interests as precursors of these compounds.

Bacteria↗

PubMed2002

Nitrite accumulation and nitric oxide emission in relation to cellular signaling in nitrite reductase antisense tobacco.

An antisense nitrite reductase (NiR, EC 1.7.7.1) tobacco ( Nicotiana tabacum L.) transformant (clone 271) was used to gain insight into a possible correlation between nitrate reductase (NR, EC 1.6.6.1)-dependent nitrite accumulation and nitric oxide (NO(.)) production, and to assess the regulation of signal transduction in response to stress conditions. Nitrite concentrations of clone 271 leaves were 10-fold, and NO(.) emission rates were 100-fold higher than in wild type leaves. Increased protein tyrosine nitration in clone 271 suggests that high NO(.) production resulted in increased peroxynitrite (ONOO(-)) formation. Tyrosine nitration was also observed in vitro by adding peroxynitrite to leaf extracts. As in mammalian cells, NO(.) and derivatives also increased synthesis of proteins like 14-3-3 and cyclophilins, which are both involved in regulation of activity and stability of enzymes.

14-3-3 Proteins↗

PubMed1987

Location and sequence of the promoter of the gene for the NADH-dependent nitrite reductase of Escherichia coli and its regulation by oxygen, the Fnr protein and nitrite.

The DNA sequence containing the start of the Escherichia coli nirB gene is reported. The N-terminal amino acid sequence of purified NADH-dependent nitrite reductase coincided with that predicted from the DNA sequence, confirming that nirB is the structural gene for nitrite reductase apoprotein and identifying the translation start point. Using nuclease S1 mapping, the sole transcription startpoint for the nirB gene was found 23 or 24 base-pairs upstream from the ATG initiation codon. By subcloning successively smaller DNA fragments into a beta-galactosidase expression vector plasmid, we located the promoter within a sequence bounded by a TaqI site at +14 with respect to the transcription startpoint and a HpaII site at -208. Measurements in vivo of beta-galactosidase expression and RNA levels due to nirB promoter activity showed that this promoter was activated during anaerobic growth. Optimal activity was found only after anaerobic growth in the presence of nitrite. The sequence of the nirB promoter is compared with sequences found at other anaerobically activated promoters.

Bacterial Proteins↗

PubMed1993

Nitrite reductase gene from Synechococcus sp. PCC 7942: homology between cyanobacterial and higher-plant nitrite reductases.

The gene encoding nitrite reductase (nir) from the cyanobacterium Synechococcus sp. PCC 7942 has been identified and sequenced. This gene comprises 1536 nucleotides and would encode a polypeptide of 56,506 Da that shows similarity to nitrite reductase from higher plants and to the sulfite reductase hemoprotein from enteric bacteria. Identities found at positions corresponding to those amino acids which in the above-mentioned proteins hold the Fe4S4-siroheme active center suggest that nitrite reductase from Synechococcus bears an active site much alike that present in those reductases. The fact that the Synechococcus and higher-plant nitrite reductases are homologous proteins gives support to the endosymbiont theory for the origin of chloroplasts.

Amino Acid Sequence↗

PubMed2005

Sensing nitrite through a pseudoazurin-nitrite reductase electron transfer relay.

Nitrite is converted to nitric oxide by haem or copper-containing enzymes in denitrifying bacteria during the process of denitrification. In designing an efficient biosensor, this enzymic turnover must be quantitatively assessed. The enzyme nitrite reductase from Alcaligenes faecalis contains a redox-active blue copper centre and a nonblue enzyme-active copper centre. It can be covalently tethered to modified gold-electrode surfaces in configurations in which direct electron transfer is possible. A surface cysteine mutant of the enzyme can be similarly immobilised on bare electroactive gold substrates. Under such circumstances, however, electron transfer cannot be effectively coupled with substrate catalytic turnover. In using either the natural redox partner, pseudoazurin, or ruthenium hexammine as an "electron-shuttle" or "conduit" between enzyme and a peptide-modified electrode surface, the coupling of electron transfer to catalysis can be utilised in the development of an amperometric nitrite sensor.

Azurin↗

PubMed1997

A nitrite biosensor based on a maltose binding protein nitrite reductase fusion immobilized on an electropolymerized film of a pyrrole-derived bipyridinium.

The preparation and electrochemical characterization of glassy carbon electrodes (GCEs) modified with electropolymerized films of the cation N-(3-pyrrol-1-yl-propyl)-4,4'-bipyridine (PPB) are described. The behavior of a new biosensor, which exhibits a high catalytic activity for nitrite reduction and which consists of a maltose binding protein nitrite reductase fusion (MBP-Nir) immobilized on an electropolymerized film of PPB as an electrocatalyst, is also described. The insoluble perchlorate salt of the poly(benzyl viologen) dication was used to immobilize MBP-Nir onto an electrode previously modified with an electropolymerized film of PPB. The electropolymerized film of PPB on the GCE is redox active and exhibits special electron-transfer properties toward the MBP-Nir layer but not toward Nir (Nir without MBP fusion attached), suggesting an intimate interaction between the PPB film and the MBP-Nir layer. The kinetics of the catalytic reaction between the biosensor and nitrite anion were characterized using cyclic voltammetry and rotated disk electrode techniques, and a value of (4.6 +/- 0.5) x 10(3) M-1 S-1 was obtained for the rate constant.

Biosensing Techniques↗

PubMed2004

Reactions of spinach nitrite reductase with its substrate, nitrite, and a putative intermediate, hydroxylamine.

Plant nitrite reductase (NiR) catalyzes the reduction of nitrite (NO(2)(-)) to ammonia, using reduced ferredoxin as the electron donor. NiR contains a [4Fe-4S] cluster and an Fe-siroheme, which is the nitrite binding site. In the enzyme's as-isolated form ([4Fe-4S](2+)/Fe(3+)), resonance Raman spectroscopy indicated that the siroheme is in the high-spin ferric hexacoordinated state with a weak sixth axial ligand. Kinetic and spectroscopic experiments showed that the reaction of NiR with NO(2)(-) results in an unexpectedly EPR-silent complex formed in a single step with a rate constant of 0.45 +/- 0.01 s(-)(1). This binding rate is slow compared to that expected from the NiR turnover rates reported in the literature, suggesting that binding of NO(2)(-) to the as-isolated form of NiR is not the predominant type of substrate binding during enzyme turnover. Resonance Raman spectroscopic characterization of this complex indicated that (i) the siroheme iron is low-spin hexacoordinated ferric, (ii) the ligand coordination is unusually heterogeneous, and (iii) the ligand is not nitric oxide, most likely NO(2)(-). The reaction of oxidized NiR with hydroxylamine (NH(2)OH), a putative intermediate, results in a ferrous siroheme-NO complex that is spectroscopically identical to the one observed during NiR turnover. Resonance Raman and absorption spectroscopy data show that the reaction of oxidized NiR ([4Fe-4S](2+)/Fe(3+)) with hydroxylamine is binding-limited, while the NH(2)OH conversion to nitric oxide is much faster.

Hydroxylamine↗

PubMed2000

Time-resolved infrared spectroscopy reveals a stable ferric heme-NO intermediate in the reaction of Paracoccus pantotrophus cytochrome cd1 nitrite reductase with nitrite.

Cytochrome cd(1) is a respiratory enzyme that catalyzes the physiological one-electron reduction of nitrite to nitric oxide. The enzyme is a dimer, each monomer containing one c-type cytochrome center and one active site d(1) heme. We present stopped-flow Fourier transform infrared data showing the formation of a stable ferric heme d(1)-NO complex (formally d(1)Fe(II)-NO(+)) as a product of the reaction between fully reduced Paracoccus pantotrophus cytochrome cd(1) and nitrite, in the absence of excess reductant. The Fe-(14)NO nu(NO) stretching mode is observed at 1913 cm(-1) with the corresponding Fe-(15)NO band at 1876 cm(-1). This d(1) heme-NO complex is still readily observed after 15 min. EPR and visible absorption spectroscopic data show that within 4 ms of the initiation of the reaction, nitrite is reduced at the d(1) heme, and a cFe(III) d(1)Fe(II)-NO complex is formed. Over the next 100 ms there is an electron redistribution within the enzyme to give a mixed species, 55% cFe(III) d(1)Fe(II)-NO and 45% cFe(II) d(1)Fe(II)-NO(+). No kinetically competent release of NO could be detected, indicating that at least one additional factor is required for product release by the enzyme. Implications for the mechanism of P. pantotrophus cytochrome cd(1) are discussed.

Cytochrome c Group↗

PubMed1990

The reaction of Pseudomonas nitrite reductase and nitrite. A stopped-flow and EPR study.

The reaction between reduced Pseudomonas nitrite reductase and nitrite has been studied by stopped-flow and rapid-freezing EPR spectroscopy. The interpretation of the kinetics at pH 8.0 is consistent with the following reaction mechanism (where k1 and k3 much greater than k2). [formula: see text] The bimolecular step (Step 1) is very fast, being lost in the dead time of a rapid mixing apparatus; the stoichiometry of the complex has been estimated to correspond to one NO2- molecule/heme d1. The final species is the fully reduced enzyme with NO bound to heme d1; and at all concentrations of nitrite, there is no evidence for dissociation of NO or for further reduction of NO to N2O. Step 2 is assigned to an internal electron transfer from heme c to reduced NO-bound heme d1 occurring with a rate constant of 1 s-1; this rate is comparable to the rate of internal electron transfer previously determined when reducing the oxidized enzyme with azurin or cytochrome c551. When heme d1 is NO-bound, the rate at which heme c can accept electrons from ascorbate is remarkably increased as compared to the oxidized enzyme, suggesting an increase in the redox potential of the latter heme.

Electron Spin Resonance Spectroscopy↗

PubMed1980

[Nitrite reduction by NADH, catalyzed by the nitrite reductase of Pseudomonas aeruginosa].

Reduction of nitrite by NADH catalyzed by Pseudomonas aeruginosa nitrite reductase is inhibited by a high concentration of nitric oxide NO. Contrary to what is currently admitted, we find that the nitrite reduction proceeds to the nitrogen monoxide N2O stage. EPR spectra show that, during the catalytic cycle, the enzyme forms specific Fe2+-NO heminic complexes.

Catalysis↗

PubMed1991

Nitrite activates the transcription of the Pseudomonas aeruginosa nitrite reductase and cytochrome c-551 operon under anaerobic conditions.

The transcription of the Pseudomonas aeruginosa denAB operon, which consists of the nitrite reductase and cytochrome c-551 genes, is induced under anaerobic conditions. However, under anaerobic non-denitrifying conditions (anaerobic growth on arginine), the promoter activity of the operon was approximately one-fifth of that under anaerobic denitrifying conditions (anaerobic growth in the presence of nitrite or nitrate). This result clearly demonstrates that the presence of nitrite or nitrate activates the transcription of P. aeruginosa denAB operon under anaerobic conditions.

Anaerobiosis↗