Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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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)

Enzymes and proteins: AO, amine oxidase; and as proposed in reference 3, BSAO, bovine serum AO; SSAO, swine serum AO; SKDAO, swine kidney AO; PSAO, pea seedling AO; APAO, arthrobacter P1AO; MADH, methylamine dehydrogenase; AAO, ascorbic acid oxidase; alpha-AE, alpha-amidating enzyme; Az, azurin; COX, cytochrome c oxidase; CP, ceruloplasmin; DBH, dopamine beta-hydroxylase; GO, galactose oxidase; Hc, hemocyanin; MT, metallotheonein; NIR, nitrite reductase; SOD, superoxide dismutase. Cofactors: Dopa, 3,4 dihydroxyphenylalanine; Topa, 3,4,6 trihydroxyphenyl-alanine; PLP, pyridoxal-phosphate; PQQ, pyrroloquinolinequinone. Reagents: DDC, diethyldithiocarbamate; DMG, diaminoguanidine; DMSA, dimercaptosuccinic acid; NTA, nitrilotriacetic acid. Technique-related: XANES, x-ray absorption near edge spectroscopy; EXAFS, extended x-ray absorption fine structure; ENDOR, electron-nuclear double resonance; ESEEM, electron spin echo envelope modulation; CD, circular dichroism; MCD, magnetic circular dichroism; NMRD, nuclear magnetic resonance dispersion; nqi, nuclear quadrupole interaction; DSC, differential scanning calorimetry.
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PMID:Copper in biological systems. A report from the 6th Manziana Conference, September 23-27, 1990. 175 86

The genes that encode the hc-type nitric-oxide reductase from Paracoccus denitrificans have been identified. They are part of a cluster of six genes (norCBQDEF) and are found near the gene cluster that encodes the cd1-type nitrite reductase, which was identified earlier [de Boer, A. P. N., Reijnders, W. N. M., Kuenen, J. G., Stouthamer, A. H. & van Spanning, R. J. M. (1994) Isolation, sequencing and mutational analysis of a gene cluster involved in nitrite reduction in Paracoccus denitrificans, Antonie Leeu wenhoek 66, 111-127]. norC and norB encode the cytochrome-c-containing subunit II and cytochrome b-containing subunit I of nitric-oxide reductase (NO reductase), respectively. norQ encodes a protein with an ATP-binding motif and has high similarity to NirQ from Pseudomonas stutzeri and Pseudomonas aeruginosa and CbbQ from Pseudomonas hydrogenothermophila. norE encodes a protein with five putative transmembrane alpha-helices and has similarity to CoxIII, the third subunit of the aa3-type cytochrome-c oxidases. norF encodes a small protein with two putative transmembrane alpha-helices. Mutagenesis of norC, norB, norQ and norD resulted in cells unable to grow anaerobically. Nitrite reductase and NO reductase (with succinate or ascorbate as substrates) and nitrous oxide reductase (with succinate as substrate) activities were not detected in these mutant strains. Nitrite extrusion was detected in the medium, indicating that nitrate reductase was active. The norQ and norD mutant strains retained about 16% and 23% of the wild-type level of NorC, respectively. The norE and norF mutant strains had specific growth rates and NorC contents similar to those of the wild-type strain, but had reduced NOR and NIR activities, indicating that their gene products are involved in regulation of enzyme activity. Mutant strains containing the norCBQDEF region on the broad-host-range vector pEG400 were able to grow anaerobically, although at a lower specific growth rate and with lower NOR activity compared with the wild-type strain.
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PMID:Mutational analysis of the nor gene cluster which encodes nitric-oxide reductase from Paracoccus denitrificans. 902 86

A heterologous expression system of the blue copper-containing nitrite reductase from Alcaligenes xylosoxidans GIFU1051 (AxgNIR) was constructed, and the purified recombinant enzyme was characterized. All the characteristic spectroscopic properties and enzyme activity of native AxgNIR were retained in the copper-reconstituted recombinant protein expressed in Escherichia coli, indicating the correct coordination of two types of Cu (type 1 and 2) in the recombinant enzyme. Moreover, two conserved noncoordinate residues, Asp98 and His255, located near the type 2 Cu site were replaced to elucidate the catalytic residue(s) of NIR. The Asp98 residue hydrogen-bonded to the water molecule ligating the type 2 Cu was changed to Ala, Asn, or Glu, and the His255 residue hydrogen-bonded to Asp98 through the water molecule was replaced with Ala, Lys, or Arg. The catalytic rate constants of all mutants were decreased to 0.4-2% of those of the recombinant enzyme, and the apparent K(m) values for nitrite were greatly increased in the Asp98 mutants. All the steady-state kinetic data of the mutants clearly demonstrate that both Asp98 and His255 are involved not only in the catalytic reaction but also in the substrate anchoring.
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PMID:Functional analysis of conserved aspartate and histidine residues located around the type 2 copper site of copper-containing nitrite reductase. 1073 3

Cytochrome cd(1) (cd(1)NIR) from Paracoccus pantotrophus, which is both a nitrite reductase and an oxidase, was reduced by ascorbate plus hexaamineruthenium(III) chloride on a relatively slow time scale (hours required for complete reduction). Visible absorption spectroscopy showed that mixing of ascorbate-reduced enzyme with oxygen at pH = 6.0 resulted in the rapid oxidation of both types of heme center in the enzyme with a linear dependence on oxygen concentration. Subsequent changes on a longer time scale reflected the formation and decay of partially reduced oxygen species bound to the d(1) heme iron. Parallel freeze-quench experiments allowed the X-band electron paramagnetic resonance (EPR) spectrum of the enzyme to be recorded at various times after mixing with oxygen. On the same millisecond time scale that simultaneous oxidation of both heme centers was seen in the optical experiments, two new EPR signals were observed. Both of these are assigned to oxidized heme c and resemble signals from the cytochrome c domain of a "semi-apo" form of the enzyme for which histidine/methionine coordination was demonstrated spectroscopically. These observations suggests that structural changes take around the heme c center that lead to either histidine/methionine axial ligation or a different stereochemistry of bis-histidine axial ligation than that found in the as prepared enzyme. At this stage in the reaction no EPR signal could be ascribed to Fe(III) d(1) heme. Rather, a radical species, which is tentatively assigned to an amino acid radical proximal to the d(1) heme iron in the Fe(IV)-oxo state, was seen. The kinetics of decay of this radical species match the generation of a new form of the Fe(III) d(1) heme, probably representing an OH(-)-bound species. This sequence of events is interpreted in terms of a concerted two-electron reduction of oxygen to bound peroxide, which is immediately cleaved to yield water and an Fe(IV)-oxo species plus the radical. Two electrons from ascorbate are subsequently transferred to the d(1) heme active site via heme c to reduce both the radical and the Fe(IV)-oxo species to Fe(III)-OH(-) for completion of a catalytic cycle.
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PMID:Oxidase reaction of cytochrome cd(1) from Paracoccus pantotrophus. 1074 91

The mutant replacing the Met86 ligand of Achromobacter cycloclastes pseudoazurin (Ac-pAz) with Gln has been prepared and spectroscopically and electrochemically characterized. Ac-pAz has four ligands (2His, Cys, and Met) and donates one electron to its cognate Cu-containing nitrite reductase (Ac-NIR). The mutant ([Met86Gln]pAz) shows the electronic absorption and CD spectra considerably similar to those of zucchini mavicyanin (Mv) and lacquer and cucumber stellacyanins (St) having 2His, Cys, and Gln. The EPR signal of the mutant has an axial character, although those of Mv and St show rhombic signals. The findings indicate that the Cu site having Gln might be a distorted trigonal geometry. The half-wave potentials (E(1/2)) of [Met86Gln]pAz and the intermolecular electron-transfer rate constant (kET) from the mutant to Ac-NIR were determined by cyclic voltammetry at pH 7.0 and 25 degrees C. The E(1/2) is +134 mV (versus NHE) and the coordination of Gln instead of Met negatively shifts the E(1/2) of Ac-pAz (+260 mV (versus NHE)). The kET of [Met86Gln]pAz (1.2x10(6) M(-1) s(-1)) is larger than that of the recombinant Ac-pAz (7.5x10(5) M(-1) s(-1)).
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PMID:Spectroscopic and electrochemical properties of the Met86Gln mutant of Achromobacter cycloclastes pseudoazurin. 1113 42

The mutant (M150Q-NIR) replacing the Met150 ligand of the type 1 Cu center in Achromobacter cycloclastes nitrite reductase (AcNIR) with Gln has been physicochemically and functionally characterized. The electronic absorption and CD spectra of M150Q-NIR are similar to those of mavicyanin and stellacyanin having the 2His, Cys, and Gln ligands, but the EPR signal has an axial character, although their blue copper proteins show rhombic EPR signals. The mutant has about 80% catalytic activity of AcNIR. Moreover, the midpoint potential (E(1/2)) of M150Q-NIR is +113 mV vs. NHE at pH 7.0, being negatively shifted compared to that of AcNIR (+240 mV). Although the intermolecular electron-transfer process from Achromobacter cycloclastes pseudoazurin (pAz) to M150Q-NIR was not detected, the pAz mutant (M86Q-pAz) replacing the Met86 ligand with Gln transfers one electron to the NIR mutant with an intermolecular electron-transfer rate constant (k(ET)) of 2.3 x 10(5)M(-1)s(-1).
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PMID:Characterization and function of Met150Gln mutant of copper-containing nitrite reductase from Achromobacter cycloclastes IAM1013. 1265 49

Nitrite reduction by cytochrome cd(1) nitrite reductase (cd(1)NIR) is currently accepted to involve coordination of the nitrite nitrogen atom to the ferrous d(1) heme. Here, density functional theory results are reported on the previously unexplored O-binding of nitrite to ferrous and ferric cd(1)NIR. Although the N-isomer (nitro) is energetically favored over the O-nitrite (nitrito), even one single strong hydrogen bond may provide the energy required to put the two isomers on level terms. When hydrogen bonding existent at the cd(1)NIR active site is accounted for in the computational model, the O-nitrite isomer is found to spontaneously protonate and thus yield a ferric-hydroxo species, liberating nitric oxide. An O-nitrite ferrous cd(1)NIR complex appears to be an energetically feasible intermediate for nitrite reduction. O-Coordination would offer an advantage since the end product of nitrite reduction would be a ferric-hydroxo/water complex, rather than the more kinetically inert iron-nitrosyl complex implied by the N-nitrite mechanism.
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PMID:Linkage isomerism in nitrite reduction by cytochrome cd1 nitrite reductase. 1518 Apr 27

Copper-containing nitrite reductase harbors a type-1 and a type-2 Cu site. The former acts as the electron acceptor site of the enzyme, and the latter is the site of catalytic action. The effect of the methionine ligand on the reorganization energy of the type-1 site was explored by studying the electron-transfer kinetics between NiR (wild type (wt) and the variants Met150Gly and Met150Thr) with Fe(II)EDTA and Fe(II)HEDTA. The mutations increased the reorganization energy by 0.3 eV (30 kJ mol-1). A similar increase was found from pulse radiolysis experiments on the wt NIR and three variants (Met150Gly, Met150His, and Met150Thr). Binding of the nearby Met62 to the type-1 Cu site in Met150Gly (under influence of an allosteric effector) lowered the reorganization energy back to approximately the wt value. According to XRD data the structure of the reduced type-1 site in Met150Gly NiR in the presence of an allosteric effector is similar to that in the reduced wt NiR (solved to 1.85 A), compatible with the similarity in reorganization energy.
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PMID:Effect of the methionine ligand on the reorganization energy of the type-1 copper site of nitrite reductase. 1722 14

The heme-containing periplasmic nitrite reductase (cd(1) NIR) is responsible for the production of nitric oxide (NO) in denitrifying bacterial species, among which are several animal and plant pathogens. Heme NIRs are homodimers, each subunit containing one covalently bound c-heme and one d(1)-heme. The reduction of nitrite to NO involves binding of nitrite to the reduced protein at the level of d(1)-heme, followed by dehydration of nitrite to yield NO and release of the latter. The crucial rate-limiting step in the catalytic mechanism is thought to be the release of NO from the d(1)-heme, which has been proposed, but never demonstrated experimentally, to occur when the iron is in the ferric form, given that the reduced NO-bound derivative was presumed to be very stable, as in other hemeproteins. We have measured for the first time the kinetics of NO binding and release from fully reduced cd(1) NIR, using the enzyme from Pseudomonas aeruginosa and its site-directed mutant H369A. Quite unexpectedly, we found that NO dissociation from the reduced d(1)-heme is very rapid, several orders of magnitude faster than that measured for b-type heme containing reduced hemeproteins. Because the rate of NO dissociation from reduced cd(1) NIR, measured in the present report, is faster than or comparable with the turnover number, contrary to expectations this event may well be on the catalytic cycle and not necessarily rate-limiting. This finding also provides a rationale for the presence in cd(1) NIR of the peculiar d(1)-heme cofactor, which has probably evolved to ensure fast product dissociation.
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PMID:Fast dissociation of nitric oxide from ferrous Pseudomonas aeruginosa cd1 nitrite reductase. A novel outlook on the catalytic mechanism. 1738 87

Tetrapyrroles are essential molecules in living organisms and perform a multitude of functions in all kingdoms. Their synthesis is achieved in cells via a complex biosynthetic machinery which is unlikely to be maintained, if unnecessary. Here we propose that ancient hemes, such as the d(1)-heme of cd(1) nitrite reductase or the siroheme of bacterial and plant nitrite and sulphite reductases, are molecular fossils which have survived the evolutionary pressure because their role is strategic for the organism where they are found today. The peculiar NO-releasing propensity of the d(1)-heme of P. aeruginosa NIR, recently shown by our group is, in our opinion, an example of this strategy. The hypothesis is that the d(1)-heme structure might be a pre-requisite for the fast rate of NO dissociation from the ferrous form, a property which is crucial to enzymatic activity and cannot be achieved with a more common b-type heme.
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PMID:Ancient hemes for ancient catalysts. 1970 34


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