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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)

Various dehydrogenases, reductases, and electron transfer proteins involved in respiratory sulfate reduction by Desulfovibrio gigas have been localized with respect to the periplasmic space, membrane, and cytoplasm. This species was grown on a lactate-sulfate medium, and the distribution of enzyme activities and concentrations of electron transfer components were determined in intact cells, cell fractions prepared with a French press, and lysozyme spheroplasts. A significant fraction of formate dehydrogenase was demonstrated to be localized in the periplasmic space in addition to hydrogenase and some c-type cytochrome. Cytochrome b, menaquinone, fumarate reductase, and nitrite reductase were largely localized on the cytoplasmic membrane. Fumarate reductase was situated on the inner aspect on the membrane, and the nitrite reductase appeared to be transmembraneous. Adenylylsulfate reductase, bisulfite reductase (desulfoviridin), pyruvate dehydrogenase, and succinate dehydrogenase activities were localized in the cytoplasm. Significant amounts of hydrogenase and c-type cytochromes were also detected in the cytoplasm. Growth of D. gigas on a formate-sulfate medium containing acetate resulted in a 10-fold increase in membrane-bound formate dehydrogenase and a doubling of c-type cytochromes. Growth on fumarate with formate resulted in an additional increase in b-type cytochrome compared with lactate-sulfate-grown cells.
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PMID:Localization of dehydrogenases, reductases, and electron transfer components in the sulfate-reducing bacterium Desulfovibrio gigas. 724 92

Desulfovibrio desulfuricans (ATCC 27774), a strictly anaerobic sulfate-reducing bacteria, is able to perform anaerobic nitrate respiration in which nitrate is first reduced to nitrite by the action of nitrate reductase, and nitrite reductase then catalyzes the six-electron reduction of nitrite to ammonia. The nitrite reductase was found to be a membrane-bound enzyme and has been purified to electrophoretic homogeneity. The purified enzyme has a minimal Mr = 66,000 as judged by sodium dodecyl sulfate gel electrophoresis and contains 6 c-type heme groups/molecule. Pure nitrite reductase exhibits a typical c-type cytochrome absorption spectrum with reduced alpha-band at 552.5 nm. NADH and NADPH do not function as direct electron donors for the nitrite reductase. Desulfovibrio vulgaris hydrogenase, however, is able to transfer electrons from H2 to the nitrite reductase using FAD as the electron transfer mediator. The dithionite-reduced nitrite reductase was demonstrated to be auto-oxidizable even in the presence of potassium cyanide. On addition of nitrite, the dithionite-reduced enzyme is re-oxidized immediately. Hydroxylamine, however, can only partially re-oxidize the reduced enzyme. Ascorbate reduces the enzyme to a limited extent and the partially reduced enzyme is neither auto-oxidizable nor re-oxidizable by nitrite or hydroxylamine. Purified nitrite reductase has a pH optimum in the range of 8.0-9.5 and optimal activity at 57 degrees C. Purified nitrite reductase also has hydroxylamine reductase activity, and the Km for nitrite was determined to be 1.14 mM and that for hydroxylamine is 113.5 mM. The difference in Km values seems to exclude the possibility of hydroxylamine being a free intermediate in the reduction of nitrite.
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PMID:The isolation of a hexaheme cytochrome from Desulfovibrio desulfuricans and its identification as a new type of nitrite reductase. 730 57

Nitric oxide (NO) reductase is an integral membrane component of the anaerobic respiratory chain of Pseudomonas stutzeri that transforms nitrate to dinitrogen (denitrification). The enzyme catalyzes the reduction of NO to nitrous oxide. The structural genes for the NO reductase complex, norC and norB, were sequenced and their organization established by primer extension and Northern blot analysis. The norCB genes encoding the cytochrome c and cytochrome b subunits of the enzyme are contiguous and transcribed as a single 2.0-kb transcript. The promoter region has a canonical recognition motif for the transcriptional activator protein Fnr, centered at -40.5 nucleotides from the initiation site of transcription. No similarity of the derived gene products to known cytochromes of b- or c-type was found in a data bank search. Post-translational processing of the two subunits was limited to the removal of the terminal methionine to leave an N-terminal serine in either subunit. The mature cytochrome c subunit (16508Da, 145 residues) is predicted to be a bitopic protein with a single membrane anchor. The mature cytochrome b subunit (53006Da, 473 residues) is a putatively polytopic, strongly hydrophobic membrane-bound protein with 12 potential transmembrane segments. Several histidine and proline residues were identified with potentially structural and/or functional importance. Mutational inactivation of NO reductase by deletion of norB or the norCB genes affected strongly the in vivo activity of respiratory nitrite reductase (cytochrome cd1), but to a much lesser extent the expression level of this enzyme. In turn, mutational inactivation of the structural gene for cytochrome cd1, nirS, or loss of in vivo nitrite reduction by mutation of the nirT gene, encoding a presumed tetraheme cytochrome, lowered the expression level of NO reductase to 5-20%, but hardly its catalytic activity. The cellular concentration of NO reductase increased again on restoration of nitrite reduction in the nirS::Tn5 mutant MK202 by complementation with nirS or with the heterologous nirK gene, encoding the Cu-containing nitrite reductase from Pseudomonas aureofaciens. Thus, NO may be required as an inducer for its own reductase. Our results show that the nitrite-reducing system and the NO-reducing system are not operating independently from each other but are interlaced by activity modulation and regulation of enzyme synthesis.
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PMID:Nitric oxide reductase from Pseudomonas stutzeri. Primary structure and gene organization of a novel bacterial cytochrome bc complex. 750 88

By using the gene encoding the C-terminal part of the cd1-type nitrite reductase of Pseudomonas stutzeri JM300 as a heterologous probe, the corresponding gene from Paracoccus denitrificans was isolated. This gene, nirS, codes for a mature protein of 63144 Da having high homology with cd1-type nitrite reductases from other bacteria. Directly downstream from nirS, three other nir genes were found in the order nirECF. The organization of the nir gene cluster in Pa. denitrificans is different from the organization of nir clusters in some Pseudomonads. nirE has high homology with a S-adenosyl-L-methionine:uroporphyrinogen III methyltransferase (uro'gen III methylase). This methylase is most likely involved in the heme d1 biosynthesis in Pa. denitrificans. The third gene, nirC, codes for a small cytochrome c of 9.3 kDa having high homology with cytochrome c55X of Ps. stutzeri ZoBell. The 4th gene, nirF, has no homology with other genes in the sequence databases and has no relevant motifs. Inactivation of either of these 4 genes resulted in the loss of nitrite and nitric oxide reductase activities but not of nitrous oxide reductase activity. nirS mutants lack the cd1-type nitrite reductase while nirE, nirC and nirF mutants produce a small amount of cd1-type nitrite reductase, inactive due to the absence of heme d1. Upstream from the nirS gene the start of a gene was identified which has limited homology with nosR, a putative regulatory gene involved in nitrous oxide reduction. A potential FNR box was identified between this gene and nirS.
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PMID:Isolation, sequencing and mutational analysis of a gene cluster involved in nitrite reduction in Paracoccus denitrificans. 774 27

In the denitrification gene cluster from Pseudomonas aeruginosa, an operon encoding three open reading frames (nirQ, ORF2, ORF3) was upstream of the structural gene for nitrite reductase (nirS) as a divergent transcriptional organization. A nucleotide-binding protein encoded by nirQ was 76% identical to the Pseudomonas stutzeri nirQ gene product, which was shown to be necessary for activating nitrite and nitric oxide reductases. The gene product of ORF2 was homologous to subunit III of cytochrome oxidases. The nirQ gene was transcribed under denitrifying conditions. The intergenic region of nirS and nirQ has only one binding motif for ANR, a regulatory protein for anaerobic gene expression correspond to FNR in E. coli. Complementation analyses showed that the transcription of both nirS and nirQ completely depended on ANR.
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PMID:Structure and ANR-dependent transcription of the nir genes for denitrification from Pseudomonas aeruginosa. 776 51

The complete amino acid sequence of cytochrome c-552 derived from the chemoautotrophic ammonia-oxidizing bacterium Nitrosomonas europaea was determined. The cytochrome consisted of 81 amino acid residues, and its molecular weight was calculated to be 9098 including heme c. Although the sequence of cytochrome c-552 was highly homologous to those of cytochromes c-551, which were known as the electron-donating components to dissimilatory nitrite reductase in pseudomonads, cytochrome c-552 differed from cytochrome c-551 in two points: (1) the sequence of cytochrome c-552 was shorter by two amino acid residues than that of cytochrome c-551 at the N-terminus and (2) one amino acid insertion was present in cytochrome c-552.
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PMID:The amino acid sequence of Nitrosomonas europaea cytochrome c-552. 776 24

A copper-containing nitrite reductase (Cu-NiR) was purified to homogeneity from the denitrifying fungus Fusarium oxysporum. The enzyme seemed to consist of two subunits with almost the same M(r) value of 41,800 and contains two atoms of copper per subunit. The electron paramagnetic resonance spectrum showed that both type 1 and type 2 copper centers are present in the protein, whereas the visible absorption spectrum exhibited a sole and strong absorption maximum at 595 nm, causing a blue but not green color. The reaction product due to the Cu-NiR was mainly nitric oxide (NO), whereas a stoichiometric amount of nitrous oxide (N2O) was formed when cytochrome P-450nor was further added to the assay system. Therefore, the denitrifying (N2O forming) nitrite reductase activity that we had detected in the cell-free extract of the denitrifying cells (Shoun, H., and Tanimoto, T. (1991) J. Biol. Chem. 266, 11078-11082) could be reconstituted upon combination of the purified Cu-NiR and P-450nor. The Km for nitrite and specific activity at pH 7.0 were estimated as 49 microM and 447 mumol NO.min-1.mg protein-1, respectively. Its activity was strongly inhibited by cyanide, carbon monoxide, and diethyldithiocarbamate, whereas enormously restored by the addition of cupric ions. An azurin-like blue copper protein (M(r) = 15,000) and a cytochrome c were also isolated from the same fungus, both of which together with cytochrome c of the yeast Saccharomyces cerevisiae were effective in donating electrons to the fungal Cu-NiR. The result suggested that the physiological electron donor of the Cu-NiR is the respiratory electron transport system. The intracellular localization of Cu-NiR was investigated, and it was suggested that the Cu-NiR localizes in an organelle such as mitochondrion. These findings showed the identity in many aspects between the fungal nitrite reductase and bacterial dissimilatory Cu-NiRs. This is the first isolation of dissimilatory NiR from a eukaryote.
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PMID:The copper-containing dissimilatory nitrite reductase involved in the denitrifying system of the fungus Fusarium oxysporum. 787 66

Monomeric nitrite reductase in an active form has been prepared by controlled succinylation of the dimeric native enzyme of Pseudomonas aeruginosa and subsequent purification. The monomeric enzyme has an optical spectrum indistinguishable from that of the native enzyme. On the other hand, circular dichroic spectra in the heme and peptide absorption regions show differences with respect to the dimer that indicate that the chemical modification and/or the dissociation into monomers somewhat perturb the chromophores' environment and the secondary structure. The (negatively charged) monomer is unable to oxidize its physiological substrates, azurin and cytochrome c551. This loss of activity is not due to monomerization, but is linked to the total net charge of the succinylated molecule, which interestingly enough acquires the ability to oxidize efficiently eukaryotic cytochrome c (which is not a substrate of the native dimeric enzyme). Stopped-flow studies show that the reduced monomer reacts with oxygen with a kinetic pattern similar to that shown by the dimeric enzyme. However, a higher reaction rate in the bimolecular binding of oxygen and a much higher oxygen affinity than for the native enzyme are observed. The evidence reported in this paper indicates that the dimeric state of Pseudomonas nitrite reductase is not a prerequisite for the ferrocytochrome c-oxygen oxidoreductase activity of this enzyme.
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PMID:Monomeric Pseudomonas aeruginosa nitrite reductase: preparation, characterization, and kinetic properties. 787 36

The biochemistry and molecular biology of nitrite reductase, a key enzyme in the dissimilatory denitrification pathway of Ps aeruginosa which reduces nitrite to NO, is reviewed in this paper. The enzyme is a non-covalent homodimer, each subunit containing one heme c and one heme d1. The reaction mechanisms of nitrite and oxygen reduction are discussed in detail, as well as the interaction of the enzyme with its macromolecular substrates, azurin and cytochrome c551. Special attention is paid to new structural information, such as the chemistry of the d1 prosthetic group and the primary sequence of the gene and the protein. Finally, results on the expression both in Ps aeruginosa and in heterologous systems are presented.
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PMID:Pseudomonas aeruginosa nitrite reductase (or cytochrome oxidase): an overview. 789 16

Ammonia-forming cytochrome c nitrite reductase from Sulfurospirillum deleyianum contains four covalently bound heme c groups/55 kDa subunit as determined by atomic absorption spectroscopy and the pyridine Fe(II)-hemochrome technique. Nitrite reductase was isolated from the membrane fraction as a monomer (M(r) 55 +/- 2 kDa) and as a heterooligomeric complex. Both the monomeric and the complex form of the enzyme exhibited a high specific activity, with up to 1050 mumol NO2-min-1 mg-1. The complex was built from four 55 kDa units and contained a 22 kDa c-type cytochrome which was absent in the monomeric form. EPR spectra of the complex displayed a prominent feature at g 4.83 (baseline crossing). This resonance, which was not observed in the spectra of the monomeric nitrite reductase, was assigned to the 22 kDa c-type cytochrome subunit. Identical results were obtained for the enzyme from Wolinella succinogenes which had been reinvestigated for comparison.
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PMID:Ammonia-forming cytochrome c nitrite reductase from Sulfurospirillum deleyianum is a tetraheme protein: new aspects of the molecular composition and spectroscopic properties. 799 30


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