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

---

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

Sulfite reductase (SiR) has been purified to homogeneity from spinach leaves. Two forms of the enzyme were separated by hydroxylapatite chromatography. One, with subunit Mr 69 000 appears to be proteolytically cleaved to give rise to the other, with subunit Mr 63 000, during the purification procedure. The two species have identical catalytic activities (on a per heme basis) when reduced methylviologen (MV+) or ferredoxin (Fdr) is used as electron donor for sulfite reduction, and they exhibit nearly identical optical and EPR spectra. Both enzyme forms exist in 50 mM phosphate buffer (pH 7.7) primarily as dimers at 20 degrees C. Spinach SiR contains 1 mol of siroheme and one Fe4S4 center per subunit. The heme iron is the high spin Fe3+ state in the enzyme as isolated. Near quantitative reduction of the Fe4S4 center by dithionite could be achieved if SiR was either converted to the CO complex or treated with 80% dimethyl sulfoxide. Spinach SiR and nitrite reductase (NiR) both catalyze Fdr-or MV+-de-pendent six-electron reductions of SO3(2)- and NO2-, as well as the two electron reduction of NH2OH. Vmax values are highest with the nitrogenous substrates. However, the Km of SiR for So3(2-), and of NiR for NO2-, is at least 2 orders of magnitude less than with either of the other substrates. Rates of reduction with Fdr as electron donor are greater than with MV+ as donor, No immunological cross-reaction could be detected between spinach SiR and Escherichia coli SiR or between spinach SiR and NiR.
...
PMID:Spinach siroheme enzymes: Isolation and characterization of ferredoxin-sulfite reductase and comparison of properties with ferredoxin-nitrite reductase. 710 2

Fundamental chemical transformations for biogeochemical cycling of sulfur and nitrogen are catalyzed by sulfite and nitrite reductases. The crystallographic structure of Escherichia coli sulfite reductase hemoprotein (SiRHP), which catalyzes the concerted six-electron reductions of sulfite to sulfide and nitrite to ammonia, was solved with multiwavelength anomalous diffraction (MAD) of the native siroheme and Fe4S4 cluster cofactors, multiple isomorphous replacement, and selenomethionine sequence markers. Twofold symmetry within the 64-kilodalton polypeptide generates a distinctive three-domain alpha/beta fold that controls cofactor assembly and reactivity. Homology regions conserved between the symmetry-related halves of SiRHP and among other sulfite and nitrite reductases revealed key residues for stability and function, and identified a sulfite or nitrite reductase repeat (SNiRR) common to a redox-enzyme superfamily. The saddle-shaped siroheme shares a cysteine thiolate ligand with the Fe4S4 cluster and ligates an unexpected phosphate anion. In the substrate complex, sulfite displaces phosphate and binds to siroheme iron through sulfur. An extensive hydrogen-bonding network of positive side chains, water molecules, and siroheme carboxylates activates S-O bonds for reductive cleavage.
...
PMID:Sulfite reductase structure at 1.6 A: evolution and catalysis for reduction of inorganic anions. 756 52

Cytochrome cd1 nitrite reductase was isolated from magnetite-containing cells of the magnetotactic bacterium Magnetospirillum (formerly Aquaspirillum) magnetotacticum, which was microaerobically cultivated under denitrifying conditions. The enzyme showed absorption maxima at 643 nm and 409 nm in the oxidized form, and at 663, 551, 522, and 418 nm in the reduced form. A distinctive split absorption band did not occur at about 550 nm. The pyridine ferrohemochrome spectra suggested the presence of heme c and heme d1 in the molecule. The enzyme was composed of two identical subunits each with a molecular mass of 54 kDa; each subunit contained one c-type and one d-type heme. The isoelectric point was 9.2. The redox potentials of heme c and heme d1 were estimated to be +191 mV and +180 mV, respectively. Although the enzyme showed cyanide-sensitive N,N,N',N'-tetramethyl-p-phenylenediamine-O2 oxidoreductase activity and N,N,N',N'-tetramethyl-p-phenylenediamine-nitrite oxidoreductase activity, the enzyme did not oxidize M. magnetotacticum ferrocytochrome c-550 and Pseudomonas aeruginosa ferrocytochrome c-551 in the presence of nitrite. Furthermore, sodium succinate did not cause the reduction of cytochrome cd1 in the crude cell-free extract prepared from the magnetite-containing bacterial cells. However, M. magnetotacticum cytochrome cd1 showed a novel Fe(II):nitrite oxidoreductase activity whereas P. aeruginosa cytochromes cd1 had no Fe(II):nitrite oxidoreductase activity. These results suggest that M. magnetotacticum cytochrome cd1 may function as a Fe(II)-oxidizing enzyme under microaerobic conditions using nitrite as electron acceptor.
...
PMID:Nitrite reductase from the magnetotactic bacterium Magnetospirillum magnetotacticum. A novel cytochrome cd1 with Fe(II):nitrite oxidoreductase activity. 758 14

Cytochrome cd1-nitrite reductase is a bifunctional enzyme that catalyzes the one-electron reduction of nitrite to nitric oxide and the four-electron reduction of oxygen to water. The 1.55 A crystal structure of the dimeric enzyme from Thiosphaera pantotropha is reported here. The protein was sequenced from the X-ray structure. Each subunit contains a covalent c heme with two axial His ligands (His-17, His-69) and a unique noncovalent d1 heme ligated by Tyr-25 and His-200. The d1 heme is the mononuclear iron center where both oxygen and nitrite reduction take place. The two types of heme are located in separate domains whose arrangement suggests a mechanism requiring domain movement during catalysis.
...
PMID:The anatomy of a bifunctional enzyme: structural basis for reduction of oxygen to water and synthesis of nitric oxide by cytochrome cd1. 773 89

Conditions for the rigorous purification of desulfoviridin, the dissimilatory sulfite reductase from the sulfate-reducing bacterium Desulfovibrio vulgaris (Hildenborough) have been established. A final purification by fast protein liquid chromatography yields at least three distinct bands that each exhibit the characteristic absorption spectrum of desulfoviridin. Two of these have been extensively characterized by amino acid analysis, isoelectric focusing, polyacrylamide gel electrophoresis, and formulation of the prosthetic centers. Each contains two pairs of [Fe4S4] and siroheme units. These results stand in marked contrast to recent work claiming significant demetallation of siroheme, excess iron content, and the presence of Fe6S6 clusters. These proposals are critically assessed in light of our results and other published work. Steady-state kinetic parameters have been determined: kcat(SO3(2-) = 0.31 mol SO3(2-).s-1.mol heme-1, Km = 0.06 mM; kcat(NO2-) = 0.038 mol NO2-.s-1.mol heme-1, Km = 0.028 mM; kcat(NH2OH) = 29 mol NH2OH.s-1.mol heme-1, Km = 48 mM. A detailed comparison is made with the Escherichia coli and spinach assimilatory sulfite reductase enzymes and spinach nitrite reductase. Highly purified samples of dissimilatory sulfite reductase display an electron paramagnetic resonance spectrum characteristic of rhombic high spin ferric heme centers, while the fully reduced enzyme shows EPR features typical of [Fe4S4] clusters. The magnetic properties of the prosthetic centers are further characterized by variable temperature experiments and spin quantitation.
...
PMID:Desulfoviridin, a multimeric-dissimilatory sulfite reductase from Desulfovibrio vulgaris (Hildenborough). Purification, characterization, kinetics and EPR studies. 803 12

The structural gene of the ferredoxin:sulphite reductase (EC 1.8.7.1) from the cyanobacterium Synechococcus PCC7942 (formerly 'Anacystis nidulans') was cloned and sequenced. The gene termed 'sir' was detected by heterologous Southern hybridisation with the structural gene cysI from Escherichia coli encoding the iron-sulphur haemoprotein of the NADPH:sulphite reductase. The open reading frame is comprised of 1875 bp encoding for a polypeptide of M(r) 70.028. The deduced amino acid sequence is 35.6% identical with the enterobacterial iron-sulphur haemoprotein. This putative fd-dependent sulphite reductase is only distantly related to the fd-dependent nitrite reductase (binary matching coefficient SAB: 0.23) or with the NADPH-sulphite reductase (SAB: 0.32). Highly conserved residues are found within the two Cys clusters forming the reactive Fe4S4-sirohaem centre of the enzyme. Expression of the sir gene using a fusion vector gave a single gene product which is immunologically related with the fd-sulphite reductase from the wild-type bacterium.
...
PMID:The ferredoxin:sulphite reductase gene from Synechococcus PCC7942. 834 57

Neurospora crassa NAD(P)H-nitrite reductase, encoded by the nit-6 gene, is a soluble, alpha2-type homodimeric protein composed of 127-kDa polypeptide subunits. This multicenter oxidation-reduction enzyme utilizes either NADH or NADPH as electron donor and possesses as prosthetic groups two iron-sulfur (Fe4S4) clusters, two siroheme groups, and two FAD molecules. The native activity of the enzyme is the NAD(P)H-dependent reduction of nitrite to ammonia. In addition, N. crassa nitrite reductase displays several partial activities in vitro, including a siroheme-independent NAD(P)H-cytochrome c reductase activity and an FAD-independent dithionite-nitrite reductase activity. These partial activities are presumed to be manifestations of discrete functional domains within the protein. A full-length nit-6 cDNA was constructed and used in developing an expression system within E. coli capable of yielding high levels of NADPH-nitrite reductase activity. Maximal expression was obtained in nirB- E. coli cells grown anaerobically at 22 +/- 1 degrees C, in conjunction with co-expression of a plasmid-borne cysG gene (encoding the rate-limiting enzyme in siroheme synthesis) and co-transformation with plasmid pGroESL (encoding bacterial chaperonins GroES and GroEL). Dissection of gene segments encoding putative functional domains within the nit-6 gene was performed. Expression of a partial cDNA construct encoding the FAD-/NAD-binding domain yielded extracts with NADPH-cytochrome c reductase activity but no NADPH-nitrite reductase activity or dithionite-nitrite reductase activity. Expression of a cDNA construct encoding the (Fe4S4)-siroheme-binding domain resulted in extracts possessing dithionite-nitrite reductase activity but no NADPH-nitrite reductase or NADPH-cytochrome c reductase activity. Analysis of site-directed mutations altering amino acid residues Cys-331 within the FAD-/NAD-binding domain and Ser-755 within the (Fe4S4)-siroheme-binding domain of the nitrite reductase demonstrated that these residues were not essential for native or partial enzyme activity. Cys-757 within the (Fe4S4)-siroheme-binding domain was essential for native enzyme activity.
...
PMID:Functional dissection and site-directed mutagenesis of the structural gene for NAD(P)H-nitrite reductase in Neurospora crassa. 879 48

The three-dimensional structures of the copper-containing enzymes ascorbate oxidase, ceruloplasmin, and nitrite reductase, comprised of multiple domains with a cupredoxin fold, are consistent with having evolved from a common ancestor. The presence or absence of copper sites has complicated ascertaining the structural and evolutionary relationship among these and related proteins. Simultaneous structural superposition of the enzyme domains and their known cupredoxin relatives shows clearly that there are at least six cupredoxin classes, and that the evolution of the conserved core of these domains is independent of the presence or absence of copper sites. Relationships among the variable loops in these structures show that the two-domain ancestor of the blue oxidases contained a trinuclear-copper interface but could not have functioned in a monomeric state. Comparison of the sequence of the copper-containing, iron-regulating protein. Ferrous transport (Fet3) from yeast to the structurally defined core and loop residues of the cupredoxins suggests specific residues that could be involved in the ferroxidase activity of Fet3.
...
PMID:Structural comparison of cupredoxin domains: domain recycling to construct proteins with novel functions. 909 85

The central tunnel of the eight-bladed beta-propeller domain of cytochrome cd1 (nitrite reductase) is seen, from a 1.28 A resolution structure, to contain hydrogen donors and acceptors that are satisfied by interaction either with water or the d1 haem. The d1 haem, although bound by an extensive network of hydrogen bonds, is not distorted in its binding pocket and is confirmed to have exactly the dioxoisobacteriochlorin structure proposed from chemical studies. A biological rationale is advanced for the undistorted structure of the d1 haem and the large number of hydrogen bonds it makes. The beta-propeller domain can be closely superimposed on that of methanol dehydrogenase despite the enzymes sharing no common sequence motifs and using a different set of interactions to "Velcro" close the propeller. The sequence and likely structural relationships between cytochrome cd1 or methanol dehydrogenase and other predicted eight-bladed beta-propeller domains in proteins, such as the pyrolloquinoline quinone-dependent alcohol dehydrogenase, are discussed and compared with other propeller proteins. From sequencing the nirS gene of Thiosphaera pantotropha, it is established that the amino acid sequence deduced previously in part from X-ray diffraction data at lower resolution was largely correct, as was the proposal that eight N-terminal amino acid residues were not seen in the structure. The unusual haem iron environments in both the c-type cytochrome domain, with His/His coordination, and the d1-type cytochrome domain with Tyr/His coordination are related to the functions of the redox centres.
...
PMID:Cytochrome cd1 structure: unusual haem environments in a nitrite reductase and analysis of factors contributing to beta-propeller folds. 919 11

Cytochrome cd1 nitrite reductase catalyses the conversion of nitrite to nitric oxide in the nitrogen cycle. The crystal structure of the oxidized enzyme shows that the d1 haem iron of the active site is ligated by His/Tyr side chains, and the c haem iron is ligated by a His/His ligand pair. Here we show that both haems undergo re-ligation during catalysis. Upon reduction, the tyrosine ligand of the d1 haem is released to allow substrate binding. Concomitantly, a refolding of the cytochrome c domain takes place, resulting in an unexpected change of the c haem iron coordination from His 17/His 69 to Met106/His69. This step is similar to the last steps in the folding of cytochrome c. The changes must affect the redox potential of the haems, and suggest a mechanism by which internal electron transfer is regulated. Structures of reaction intermediates show how nitric oxide is formed and expelled from the active-site iron, as well as how both haems return to their starting coordination. These results show how redox energy can be switched into conformational energy within a haem protein.
...
PMID:Haem-ligand switching during catalysis in crystals of a nitrogen-cycle enzyme. 931 86


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---