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:1.9.3.1 (cytochrome oxidase)
8,822 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Heme a3+ isolated from bovine cardiac muscle cytochrome oxidase has been converted to the bis-imidazole species and studied by magnetic circular dichroism (MCD) spectroscopy. Spectra have been recorded down to 1.5 degrees K, enabling the MCD magnetization curves to be measured at a number of wavelengths in the visible and near infrared regions. The experimentally determined curves show excellent correlation to a curve using the g-values determined by electron paramagnetic resonance spectroscopy to be gz = 2.96, gy = 2.29, and gx = 1.73. The data show that the bis-imidazole derivative of extracted heme a3+ is an excellent model of cytochrome a in the enzyme, confirming the presence of two histidine residues in the protein as the fifth and sixth ligands. The spectral features of heme a3+ bis-imidazole in the near infrared region are consistent with transitions of the porphyrin ( a1u , a2u ) to ferric (eg) charge transfer type.
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PMID:Low temperature magnetic circular dichroism spectra and magnetization properties of extracted heme a3+ bis-imidazole. A model of cytochrome a in bovine cytochrome c oxidase. 632 4

The iron-carbon monoxide stretching mode and the iron-carbon-oxygen bending mode in carbon monoxide-bound cytochrome oxidase have been assigned at 520 and 578 cm-1, respectively. The frequencies, widths, and intensities of these modes show that the Fe-C-O grouping in carbon monoxide-cytochrome a3 is linear but tilted from the normal to the heme plane; that the iron-histidine bond in both five- and six-coordinate cytochrome a3 is strained; and that the carbon monoxide and the proximal histidine each have characteristic, well-defined orientations in all molecules. These data can account for the binding affinities of carbon monoxide and dioxygen under physiological conditions.
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PMID:Cytochrome a3 structure in carbon monoxide-bound cytochrome oxidase. 633 Aug 90

The secondary structure of the C-terminal region of all blue copper proteins can be assigned to two beta strands and a connecting segment that contains a potential histidine ligand. A similar assignment is made for the second probable blue (Type 1) site that is located in the middle fragment of ceruloplasmin also. The secondary structure regions for stellacyanin and subunit II of cytochrome oxidase predicted by the Chou-Fasman method are compared to those found in the crystal structures of plastocyanin and azurin.
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PMID:Blue copper sites and analogous sites in copper-containing oxidases: a structural description. 641 68

Cytochrome-c oxidase contains an unusual copper centre (CuA) located in subunit II. This centre mediates one-electron transfer from cytochrome c to low-spin heme a. Recent spectroscopic and biochemical studies have shown that this centre is a valence delocalised dinuclear [Cu(+1.5)-Cu(+1.5)] centre. We have measured the absorption, EPR and variable-temperature magnetic circular dichroism spectra of the CuA-binding domain isolated from Paracoccus denitrificans cytochrome aa3. The EPR spectrum showed the following signals: gparallel = 2.18; gperpendicular = 2.03. gparallel exhibited a seven-line hyperfine splitting pattern, with an intensity ratio showing that the single unpaired electron interacted equally with two copper nuclei. The magnetic circular dichroism spectrum was identical to those from CuA in bovine heart cytochrome-c oxidase and centre A of nitrous-oxide reductase, showing the close structural similarity between the three centres. To identify the ligands of CuA, all the conserved putative ligands in the P. denitrificans CuA domain were substituted. Only five residues, Cys244, Cys248, His209, His252, and Met255, were required for correct assembly of the CuA centre. Replacement of Met255 caused protein misfolding. Hence, methionine may have a structural role for the folding of the protein rather than being a CuA ligand. Given that both copper ions must have identical coordination geometries, the number of possible structures is limited. Two models are proposed: one involves the thiolate side-chains of Cys244 and Cys248 bridging a pair of copper ions with one histidine coordinating each copper ion, and the other has terminal ligation of each copper ion by one cysteine and one histidine residue. In both models, the metal-metal distance can be sufficiently short to permit direct d-orbital overlap of the copper ions. The magnetic circular dichroism transitions at 475 nm and 525 nm are assigned to thiolate-to-copper charge-transfer processes polarised perpendicular to one another, although the magnetic circular dichroism intensities show that the excited states were heavily mixed with copper d-orbitals. These intensities can be interpreted in the thiolate bridged model in terms of transitions within a Cu2(SR)2 rhomb. In the model involving terminal cysteine ligation, exciton coupling of two thiolate-to-copper charge-transfer transitions of similar energy, polarised along the Cu-S bonds, would contribute two transitions perpendicular to one another. This requires that the cysteine ligands have a cis orientation relative to one another.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Spectroscopic and mutagenesis studies on the CuA centre from the cytochrome-c oxidase complex of Paracoccus denitrificans. 755 64

We examined the regulation of Neurospora crassa arg-2 and cpc-1 in response to amino acid availability.arg-2 encodes the small subunit of arginine-specific carbamoyl phosphate synthetase; it is subject to unique negative regulation by Arg and is positively regulated in response to limitation for many different amino acids through a mechanism known as cross-pathway control. cpc-1 specifies a transcriptional activator important for crosspathway control. Expression of these genes was compared with that of the cytochrome oxidase subunit V gene, cox-5. Analyses of mRNA levels, polypeptide pulse-labeling results, and the distribution of mRNA in polysomes indicated that Arg-specific negative regulation of arg-2 affected the levels of both arg-2 mRNA and arg-2 mRNA translation. Negative translational effects on arg-2 and positive translational effects on cpc-1 were apparent soon after cells were provided with exogenous Arg. In cells limited for His, increased expression of arg-2 and cpc-1, and decreased expression of cox-5, also had translational and transcriptional components. The arg-2 and cpc-1 transcripts contain upstream open reading frames (uORFs), as do their Saccharomyces cerevisiae homologs CPA1 and GCN4. We examined the regulation of arg-2-lacZ reporter genes containing or lacking the uORF start codon; the capacity for arg-2 uORF translation appeared critical for controlling gene expression.
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PMID:Translational regulation in response to changes in amino acid availability in Neurospora crassa. 756 72

Wild-type and several mutants of cytochrome c oxidase from Rhodobacter sphaeroides were characterized by EPR spectroscopy. A pH-induced g12 signal, seen previously in mammalian cytochrome oxidase and assigned to the presence of a bridging carboxyl ligand in the bimetallic cytochrome a3-CuB site, is found also in the bacterial enzyme. Mutation of glutamate-286 to glutamine inactivates the enzyme but does not affect this signal, demonstrating that the carboxyl group of this residue is not the bridging ligand. Three mutants, M106Q, located one helix turn below a histidine ligand to cytochrome a, and T352A as well as F391Q, located close to the bimetallic center, are shown to affect dramatically the low-spin heme signal of cytochrome a. These mutants are essentially inactive, suggesting that these three mutations result in alterations to cytochrome a that render the oxidase non-functional.
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PMID:EPR studies of wild-type and several mutants of cytochrome c oxidase from Rhodobacter sphaeroides: Glu286 is not a bridging ligand in the cytochrome a3-CuB center. 758 73

The electronic structure and spectrum of several models of the binuclear metal site in soluble CuA domains of cytochrome-c oxidase have been calculated by the use of an extended version of the complete neglect of differential overlap/spectroscopic method. The experimental spectra have two strong transitions of nearly equal intensity around 500 nm and a near-IR transition close to 800 nm. The model that best reproduces these features consists of a dimer of two blue (type 1) copper centers, in which each Cu atom replaces the missing imidazole on the other Cu atom. Thus, both Cu atoms have one cysteine sulfur atom and one imidazole nitrogen atom as ligands, and there are no bridging ligands but a direct Cu-Cu bond. According to the calculations, the two strong bands in the visible region originate from exciton coupling of the dipoles of the two copper monomers, and the near-IR band is a charge-transfer transition between the two Cu atoms. The known amino acid sequence has been used to construct a molecular model of the CuA site by the use of a template and energy minimization. In this model, the two ligand cysteine residues are in one turn of an alpha-helix, whereas one ligand histidine is in a loop following this helix and the other one is in a beta-strand.
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PMID:The CuA center of cytochrome-c oxidase: electronic structure and spectra of models compared to the properties of CuA domains. 763 62

We have studied the structure of the CuB site in the binuclear heme-copper center of the fully oxidized form of the quinol-oxidizing cytochrome aa3-600 from Bacillus subtilis by EXAFS and ENDOR spectroscopy. This enzyme is member of the large superfamily of heme-copper respiratory oxidases, which catalyze the reduction of dioxygen to water and link it to translocation of protons across the bacterial or mitochondrial membrane. The EXAFS of the CuB site strongly suggests tetragonal coordination by two or three histidines with one or two O/N donor ligands. There are some indications that a Cl- ion might fractionally occupy substitution-labile sites, although the majority of enzyme molecules did not contain any heavy (second row) scatters, indicative of a Cl- (or S) bridge between the heme iron and CuB [cf. Powers, L., et al. (1994) Biochim. Biophys. Acta 1183, 504-512]. Proton ENDOR spectroscopy of the CuB site in 1H2O and 2H2O media showed evidence of an oxygenous copper ligand with an exchangeable proton. 14N ENDOR revealed three inequivalent nitrogenous ligands with hyperfine coupling constants consistent with histidines. Together, these results strongly suggest that the fully oxidized enzyme has a low-symmetry, tetragonal CuB site with three histidine nitrogens and one oxygen as ligands, the latter with an exchangeable proton(s). The identity and assignment of these ligands are discussed.
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PMID:Structure of CuB in the binuclear heme-copper center of the cytochrome aa3-type quinol oxidase from Bacillus subtilis: an ENDOR and EXAFS study. 764 Feb 80

Substoichiometric amounts of Mn are bound by the aa3-type cytochrome c oxidase of Rhodobacter sphaeroides and appear in the EPR spectrum of the purified enzyme as signals that overlay those of CuA in the g = 2.0 region. The Mn is tightly bound and not removed by a high degree of purification or by washing with 50 mM EDTA. The amount of bound Mn varies with the ratio of Mg to Mn in the growth medium. Oxidase containing no EPR-detectable Mn can be prepared from cells grown in low Mn/Mg, while high Mn/Mg in the growth medium gives rise to near stoichiometric levels (0.7 mol/mol of aa3). Incubation of purified Mn-deficient oxidase with 1 mM Mn does not allow incorporation into the tight binding site, indicating that this site is not accessible in the assembled protein. When bound Mn is depleted by growth in high Mg, there is no change in electron transfer activity, suggesting that Mg may substituted for Mn and maintain protein structure. Analysis of site-directed mutants in an extramembrane loop close to the active site of cytochrome oxidase identifies His-411 and Asp-412 of subunit I as probable ligands of the Mn. Mutation of either residue leads to lower activity and loss of Mn binding, even in cells grown in elevated concentrations of Mn. Since Mn binding correlates with the [Mn] to [Mg] ratio in the culture medium, we propose that Mn competes for the site that normally binds a stoichiometric Mg ion in aa3-type cytochrome c oxidases.
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PMID:Analysis of site-directed mutants locates a non-redox-active metal near the active site of cytochrome c oxidase of Rhodobacter sphaeroides. 777 4

Complete DNA sequences encoding the Arabidopsis thaliana STP1 monosaccharide/H+ symporter or a histidine-tagged STP1-His6 protein were expressed in baker's yeast Saccharomyces cerevisiae. Both wild-type STP1 and the recombinant his-tagged protein were located in the plasma membranes of transformed yeast cells. The C-terminal modification caused no loss of transport activity compared with the wild-type protein. Anti-STP1-antibodies were used to confirm the identity of the protein in yeast and to compare the apparent molecular weights of STP1 proteins in membrane extracts from yeast or Arabidopsis thaliana. Purified yeast plasma membranes were fused with proteoliposomes consisting of Escherichia coli lipids and beef heart cytochrome-c oxidase. Addition of ascorbate/TMPD/cytochrome-c to these fused vesicles caused an immediate formation of membrane potential (inside negative; monitored with [3H]tetraphenylphosphonium cations) and a simultaneous, uncoupler-sensitive influx of D-glucose into the energized vesicles. STP1-His6 protein is functionally active after solubilization with octyl-beta-D-glucoside, which was shown by insertion of the protein into proteoliposomes by detergent dilution and determination of the resulting transport capacity. Detergent extracts from either total membranes or plasma membranes of transgenic yeast cells were used for one-step purification of the STP1-His6 protein on Ni(2+)-NTA columns. The identity of the purified protein was checked by immunoblotting and N-terminal sequencing.
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PMID:Functional reconstitution of the solubilized Arabidopsis thaliana STP1 monosaccharide-H+ symporter in lipid vesicles and purification of the histidine tagged protein from transgenic Saccharomyces cerevisiae. 792 Jul 12


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