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Query: EC:1.7.1.4 (nitrite reductase)
 1,847 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

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.
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PMID:Sensing nitrite through a pseudoazurin-nitrite reductase electron transfer relay. 1590 May 23

Nitrite reductase is an enzyme operating in the denitrification pathway which catalyses the conversion of nitrite (NO2(-)) to gaseous nitric oxide (NO). Here, crystal structures of the oxidized and reduced forms of the copper-containing nitrite reductase from Rhodobacter sphaeroides 2.4.3 are presented at 1.74 and 1.85 A resolution, respectively. Whereas the structure of the enzyme is very similar to those of other copper-containing nitrite reductases, folding as a trimer and containing two copper sites per monomer, the structures reported here enable conformational differences between the oxidized and reduced forms of the enzyme to be identified. In the type 1 copper site, a rotational perturbation of the side chain of the copper ligand Met182 occurs upon reduction. At the type 2 copper site, a dual conformation of the catalytic residue His287 is observed in the oxidized structure but is lacking in the reduced structure, such that the interactions of the oxidized type 2 copper ion can be regarded as adopting octahedral geometry. These findings shed light on the structural mechanism of the reduction of a copper-bound nitrite to nitric oxide and water.
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PMID:Structures of the oxidized and reduced forms of nitrite reductase from Rhodobacter sphaeroides 2.4.3 at high pH: changes in the interactions of the type 2 copper. 1613 51

Nitrite reduction is the key step in the denitrification reaction with two predominant types of nitrite reductase genes: nirS and nirK. The diversity of denitrifying bacteria in a municipal wastewater treatment plant is described by using both these genes. Of the cultured colonies, 22.5% contained the NirS gene and 12.5% the nirK gene. These nitrite reductase-containing colonies could be further divided into five different types by using both restriction fragment length polymorphism and denaturing gradient gel electrophoresis analysis. Phylogenetic analysis showed that these five types of denitrifying bacteria were phylogenetically diverse. Finally, one nirS gene was obtained and compared with the published sequences.
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PMID:Identification of denitrifying bacteria diversity in an activated sludge system by using nitrite reductase genes. 1623 Dec 19

The ability of Neisseria meningitidis to utilize both oxygen and nitrogen oxides as respiratory substrates allows it to thrive in the diverse environment of the human host. Genome analysis highlighted genes encoding a cbb(3) cytochrome oxidase, the aniA nitrite reductase gene and the norB nitric oxide reductase gene. In the present study, we used myxothiazol as an inhibitor of the bc(1) complex in intact cells and demonstrated that electron flow to nitrite reductase and the cytochrome oxidase, but not NO reductase, passes via the cytochrome bc(1) complex. UV-visible spectrophotometry of intact cells demonstrated that oxygen oxidizes c-type and b-type cytochromes. Oxidation of cytochromes by nitrite was only seen in microaerobically precultured whole cells, and the predominant oxidizable cytochromes were b-type. These are likely to be associated with the oxidation of a b-haem-containing nitric oxide reductase. Nitrite inhibits the oxidation of cytochromes by oxygen in a nitrite reductase-independent manner, indicating that nitrite may inhibit oxidase activity directly, as well as via the intermediate of denitrification, nitric oxide.
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PMID:Organization of the respiratory chain of Neisseria meningitidis. 1641 4

Severely Ca-deficient Triticum aestivum L. seedlings accumulated high levels of nitrite and moderate levels of nitrate and organic nitrogen, but contained unaltered levels of hydroxylamine. Nitrite accumulation was not related to molybdenum deficiency, or altered cellular pH. Nitrate reductase was decreased by Ca deficiency, apparently by repression of enzyme synthesis from accumulated nitrite and not by inhibition of enzyme activity. Nitrite reductase and NADP diaphorase activities were not affected by Ca deficiency, and Ca did not restore activity to nitrite reductase inactivated by cyanide. The results indicated that the role of Ca is in intracellular transport of nitrite and not in induction or activity of enzymes.
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PMID:Evidence for a role of calcium in nitrate assimilation in wheat seedlings. 1665 39

A method has been devised for the detection and measurement of nitrite reductase activity in intact barley (Hordeum vulgare L. cv. Himalaya) aleurone layers. The technique involves feeding aleurone layers nitrite and measuring nitrite disappearance after a given time period. The method also allows simultaneous determination of nitrite uptake by the tissue. Quantitative recovery of nitrite is obtained by rapid heating of tissue in the presence of dimethyl sulfoxide.Using the procedure described, nitrite reductase activity in intact barley aleurone layers was determined. Enzyme activity was increased by prior incubation of the tissue with nitrate, but considerable activity was present in tissue incubated without nitrate. Nitrate-induced activity was inhibited by cycloheximide but not by actinomycin D. Enzyme activity in induced layers was inhibited by 2,4-dinitrophenol, and partially by antimycin A and 2-n-heptyl-4-hydroxyquinoline N-oxide. Activity in noninduced tissue appeared to be less sensitive to these respiratory inhibitors. In contrast, both activities were inhibited more than 90% by anaerobiosis; but nitrate-induced and noninduced aleurone layers were able to reduce nitrite anaerobically when the concentration of substrate in the assay medium was reduced from 250 mum to 25 mum. Nitrite uptake was relatively insensitive to anaerobiosis and to the inhibitors tested.Nitrite depletion from the medium by aleurone layers was rapid at pH 4.5 and negligible at pH 7.5. Nitrite accumulated at pH 4.5 under anaerobic conditions was rapidly released when the tissue was transferred to medium at pH 7.5. Nitrite release at pH 7.5 occurred whether the tissue was maintained under anaerobic or aerobic conditions.
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PMID:Intact tissue assay for nitrite reductase in barley aleurone layers. 1665 6

Nitrite reductase from green leaves of corn (Zea mays L.) is eluted from a diethylaminoethyl-cellulose column in one peak of activity by a chloride gradient, while nitrite reductase from scutellum tissue is resolved into two peaks of activity, apparently representing two forms of the enzyme NiR1 and NiR2. One of these (NiR2) elutes at the same concentration of chloride as the leaf nitrite reductase. Roots and etiolated shoots also exhibited both forms of the enzyme, however, lesser amounts of NiR1 is extractable from these tissues than from scutellum. Comparison of green leaf nitrite reductase with NiR2 from scutellum tissue shows similar or identical properties with respect to molecular weight, isoelectric point, electron donor requirements, inhibition properties, pH optima, thermal stability, and pH tolerance. The significance of these similarities in relation to probable differences in the biochemical mechanism of nitrite reduction between leaf and scutellum tissues is discussed. Although ferredoxin is considered, with some reservations, to be the electron donor for nitrite reductase in green tissue, the reductant for nongreen tissue is not known. The possibility that nitrite reductases from green and non-green tissues uses the same electron donor, in vivo, is considered.
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PMID:A Comparison of Nitrite Reductase Enzymes from Green Leaves, Scutella, and Roots of Corn (Zea mays L.). 1665 56

When excised embryos of Agrostemma githago were incubated with nitrate, the activities of both nitrate reductase and nitrite reductase were enhanced. By contrast, benzyladenine induced nitrate reductase only. Our data suggest that nitrate affected nitrite reductase activity directly, without first being reduced to nitrite. When the endogenous nitrite production was increased by raising the level of nitrate reductase through simultaneous treatment with nitrate and benzyladenine, the activity of nitrite reductase was not higher than in embryos treated with nitrate alone. On the other hand, tungstate given together with nitrate drastically inhibited the development of nitrate reductase activity without reducing the enhancement of nitrite reductase activity. Nitrite enhanced nitrite reductase activity, though less efficiently than nitrate.
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PMID:Control of Nitrite Reductase Activity in Excised Embryos of Agrostemma githago. 1665 83

The effects of nitrogen source NO(3) (-) or NH(4) (+) on nitrogen metabolism during the first 2 weeks of germination of the rice seedling (Oryza sativa L., var. IR22) grown in nutrient solution containing 40 mug/ml N were studied. Total, soluble protein, and free amino N levels were higher in the NH(4) (+)-grown seedling, particularly during the 1st week of germination. Asparagine accounted for most of the difference in free amino acid level, in both the root and the shoot. Nitrate and nitrite reductase activities were present mainly in the shoot and were higher in the NO(3) (-)-grown seedling, whereas the activity of glutamate dehydrogenase and glutamine synthetase in the root tended to be lower than that of the NH(4) (+)-grown seedling during the 1st week of germination. Glycolate oxidase and catalase activities were present mainly in the shoot. Maximum activity of the above five enzymes occurred 7 to 10 days after germination. Differences in the zymograms of nitrate reductase, glutamate dehydrogenase, and catalase were mainly between shoot and root and not from N source. Nitrite reductase bands were observed only in plants grown in plants grown in NO(3) (-).Ten-day-old seedlings of three rices differing in level of grain protein did not differ in the level of N fractions and of enzyme activities, which were consistent with their differences in grain protein content.
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PMID:Aspects of nitrogen metabolism in the rice seedling. 1665

The nitrite-reducing activity of the normal susceptible biotype of lambsquarters (Chenopodium album L.) was strongly inhibited by atrazine in the assay medium, both in the case of the in vivo assays of leaf discs in light, and in vitro photoreduction assays of crude extracts. In vitro assays of crude extracts with methylviologen or ferredoxin supplying the reducing potential were not inhibited by atrazine. In the resistant biotype, inhibition of nitrite reduction did not occur with any of the above assays. Thus, it appears that atrazine does not inhibit nitrite reductase itself, but rather the availability of photosynthetically supplied electrons for the reduction. Atrazine had no effect when added to the media for either in vivo or in vitro assays of nitrate reduction by either the susceptible or resistant biotype.Young lambsquarters plants were treated with atrazine by spraying the leaves at a rate which was lethal for susceptible plants after 5 or 6 days, but had little effect on the resistant biotype. Nitrite did not accumulate in either biotype, but remained present at the level of about 0.1 microgram nitrite N per gram fresh weight. The nitrate content of susceptible-type leaves did increase to two or three times the initial level, during the first four days after spraying. Usually the only visible effect on the plants during this time was a decreased growth rate. Twenty-four hours after spraying the following activities had fallen to 25% or less of the activities of solvent-sprayed control plants: in vivo nitrite reductase, in vivo nitrate reductase, in vitro NADH-nitrate reductase, in vitro reduced flavin mononucleotidenitrate reductase, and in vitro NADH-diaphorase. In these atrazine-treated plants, in vitro nitrite reductase activity with reducing potential supplied by methylviologen was not affected, nor were any of the above activities in leaves of atrazine-treated resistant plants. The abrupt fall in nitrate reductase represents an effect of atrazine not directly related to inhibition of photosynthesis.
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PMID:Reduction of Nitrate and Nitrite in Lambsquarters (Chenopodium album) Biotypes Resistant and Susceptible to Atrazine Toxicity. 1666 20


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