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Query: UNIPROT:O14944 (EPR)
 13,097 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Stigmatellin, a chromone inhibitor acting at the Q0 center of the bc1 complex, binds to the heme b-566 domain of cytochrome b as well as to the Fe2S2 protein. Its binding induces a shift of the alpha-band of heme b-566 to 568 nm. It does not influence the ligand field of the heme b-562 center. Concomitant with the red shift, stigmatellin gives rise to an alteration of the EPR line shape of the Fe2S2 cluster, namely linewidth narrowing and g value shifts at all 3 principal values. The midpoint redox potential of the Fe2S2 protein is shifted from 290 to 540 mV.
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PMID:The chromone inhibitor stigmatellin--binding to the ubiquinol oxidation center at the C-side of the mitochondrial membrane. 298 42

A simple procedure for preparation of highly purified soluble succinate-ubiquinone reductase from bovine heart mitochondrial particles is described. The enzyme exhibits four major bands on sodium dodecyl sulfate gel electrophoresis and contains (nmol per mg protein): covalently bound flavin, 6; non-heme iron, 53; acid-labile sulfur, 50; cytochrome b-560 heme, 1.2. The enzyme catalyzes thenoyltrifluoroacetone, or carboxin-sensitive (pure non-competitive with Q2) reduction of Q2 by succinate with a turnover number close to that in parent submitochondrial particles. The succinate reduced enzyme exhibits ferredoxin-type iron-sulfur center EPR-signal (g = 1.94 species) and a semiquinone signal (g = 2.00). An oxidized preparation shows a symmetric signal centered around g = 2.01. An unusual dissociation of the enzyme in the absence of a detergent is described. When added to the assay mixture from a concentrated protein-detergent solution, the enzyme does not reduce Q2 being highly reactive towards ferricyanide ('low Km ferricyanide reactive site'; Vinogradov, A.D., Gavrikova, E.V. and Goloveshkina, V.G. (1975) Biochem. Biophys. Res. Commun. 65, 1264-1269). The ubiquinone reductase, not the ferricyanide reductase was observed when the enzyme was added to the assay mixture from the diluted protein-detergent solutions. Thus the dissociation of succinate dehydrogenase from the complex occurs in the absence of a detergent dependent on the concentration of the protein-detergent complex in the stock preparation where the samples for the assay are taken from. An active antimycin-sensitive succinate-cytochrome c reductase was reconstituted by admixing of the soluble succinate-ubiquinone reductase and the cytochrome b-c1 complex, i.e., from the complexes which both contain the ubiquinone reactivity conferring protein (QPs). Cytochrome c reductase was also reconstituted from the succinate-ubiquinone reductase and succinate-cytochrome c reductase containing inactivated succinate dehydrogenase. The reconstitution experiments suggest that there exists a specific protein-protein (or lipid) interaction between QPs and a certain component(s) of the b-c1 complex.
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PMID:Studies on the succinate dehydrogenating system. Isolation and properties of the mitochondrial succinate-ubiquinone reductase. 299 19

A non-photosynthetic mutant (Ps-) of Rhodopseudomonas capsulata, designated R126, was analyzed for a defect in the cyclic electron transfer system. Compared to a Ps+ strain MR126, the mutant was shown to have a full complement of electron transfer components (reaction centers, ubiquinone-10, cytochromes b, c1, and c2, the Rieske 2-iron, 2-sulfur (Rieske FeS) center, and the antimycin-sensitive semiquinone). Functionally, mutant R126 failed to catalyze complete cytochrome c1 + c2 re-reduction or cytochrome b reduction following a short (10 microseconds) flash of actinic light. Evidence (from flash-induced carotenoid band shift) was characteristic of inhibition of electron transfer proximal to cytochrome c1 of the ubiquinol-cytochrome c2 oxidoreductase. Three lines of evidence indicate that the lesion of R126 disrupts electron transfer from quinol to Rieske FeS: 1) the degree of cytochrome c1 + c2 re-reduction following a flash is indicative of electron transfer from Rieske FeS to cytochrome c1 + c2 without redox equilibration with an additional electron from a quinol; 2) inhibitors that act at the Qz site and raise the Rieske FeS midpoint redox potential (Em), namely 5-undecyl-6-hydroxy-4,7-dioxobenzothiazole or 3-alkyl-2-hydroxy-1,4-napthoquinone, have no effect on cytochrome c1 + c2 oxidation in R126; 3) the Rieske FeS center, although it exhibits normal redox behavior, is unable to report the redox state of the quinone pool, as metered by its EPR line shape properties. Flash-induced proton binding in R126 is indicative of normal functional primary (QA) and secondary (QB) electron acceptor activity of the photosynthetic reaction center. The Qc functional site of cytochrome bc1 is intact in R126 as measured by the existence of antimycin-sensitive, flash-induced cytochrome b reduction.
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PMID:Discrete catalytic sites for quinone in the ubiquinol-cytochrome c2 oxidoreductase of Rhodopseudomonas capsulata. Evidence from a mutant defective in ubiquinol oxidation. 300 Oct 72

The purified cytochrome b-c1 complex of Rhodopseudomonas sphaeroides has two b cytochromes distinguishable by optical, thermodynamic and electron paramagnetic resonance criteria (gz values are approximately equal to 3.75 and approximately equal to 3.4). EPR features typical of a Rieske iron sulfur cluster (g values of 2.03 1.90 and 1.81) and a c1 type cytochrome (g approximately equal to 3.4) were also observed. The b and c1 cytochromes were individually purified from the complex. The cytochrome c1 retained its native EPR spectrum. The b cytochrome lost over 90% of the intensity from the 'b566 type' heme site (g approximately equal to 3.75), while the 'b561 type' heme site (g approximately equal to 3.4) retained its native EPR spectrum.
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PMID:The EPR spectra of the cytochrome b-c1 complex of Rhodopseudomonas sphaeroides. 301 Sep 86

A ubiquinol-cytochrome c oxidoreductase (cytochrome bc1) complex has been purified from the plasma membrane of aerobically grown Paracoccus denitrificans by extraction with dodecyl maltoside and ion exchange chromatography of the extract. The purified complex contains two spectrally and thermodynamically distinct b cytochromes, cytochrome c1, and a Rieske-type iron-sulfur protein. Optical spectra indicate absorption peaks at 553 nm for cytochrome c1 and at 560 and 566 nm for the high and low potential hemes of cytochrome b. The spectrum of cytochrome b560 is shifted to longer wavelength by antimycin. The Paracoccus bc1 complex consists of only three polypeptide subunits. On the basis of their relative electrophoretic mobilities, these have apparent molecular masses of 62, 39, and 20 kDa. The 62- and 39-kDa subunits have been identified as cytochromes c1 and b, respectively. The 20-kDa subunit is assumed to be the Rieske-type iron-sulfur protein on the basis of its molecular weight and the presence of an EPR-detectable signal typical of this iron-sulfur protein in the three-subunit complex. The Paracoccus bc1 complex catalyzes reduction of cytochrome c by ubiquinol with a turnover of 470 s-1. This activity is inhibited by antimycin, myxothiazol, stigmatellin, and hydroxyquinone analogues of ubiquinone, all of which inhibit electron transfer in the cytochrome bc1 complex of the mitochondrial respiratory chain. The electron transfer functions of the Paracoccus complex thus appear to be similar, and possibly identical, to those of the bc1 complex of eukaryotic mitochondria. The Paracoccus bc1 complex has the simplest subunit composition and one of the highest turnover numbers of any bc1 complex isolated from any species to date. These properties suggest that the structural requirements for electron transfer from ubiquinol to cytochrome c are met by a small number of peptides and that the "extra" peptides occurring in the mitochondrial bc1 complexes serve some other function(s), possibly in biogenesis or insertion of the complex into that organelle.
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PMID:Purification of a three-subunit ubiquinol-cytochrome c oxidoreductase complex from Paracoccus denitrificans. 301 70

Stigmatellin and DNP-INT are effective inhibitors of the catalytic activity of the plastoquinol-plastocyanin oxidoreductase complex (cytochrome b6-f complex). Both inhibitors alter the EPR spectrum of the Rieske iron-sulfur center but do not produce band-shifts of cytochrome b-563. The midpoint redox potential of the Rieske center is unaffected by either inhibitor, although both alter the DBMIB-induced g-value shifts of the Rieske center. The results are considered in terms of binding domains for inhibitors in the cytochrome b6-f complex.
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PMID:Interaction of stigmatellin and DNP-INT with the Rieske iron-sulfur center of the chloroplast cytochrome b6-f complex. 302 41

The EPR spectra of cytochrome b-562 isolated from the cytochrome b-c1 complex of Rhodopseudomonas sphaeroides were measured at liquid helium temperature. The purified cytochrome b-562 gives a high spin signal at g = 6.0. Anaerobic titration of this signal confirmed the presence of two redox components with Em = 40 and -110 mV at pH 7.5. These values are consistent with the published ones, Em = 55 and -100 mV at pH 7.0, that were optically estimated for the same type of preparation (Iba et al. (1985) FEBS Lett. 183, 151-154). The power saturation behavior of the g = 6.0 signal at different redox potentials indicated a direct spin-spin interaction between these two redox centers.
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PMID:Characterization by EPR spectroscopy of cytochrome b-562 isolated from the cytochrome b-c1 complex of Rhodopseudomonas sphaeroides R-26. 303 16

The pre-steady-state kinetics of the reduction of the prosthetic groups of QH2:cytochrome c oxidoreductase in bovine heart submitochondrial particles were studied in relation to the kinetics of the Q-10 reduction, using duroquinol as substrate. The prosthetic groups, including semiquinone, were measured with EPR and low-temperature-diffuse reflectance spectroscopy, the samples being prepared with the rapid-freeze quench technique. For the determination of the redox state of ubiquinone in the pre-steady state the rapid chemical quench technique was used as an extension of the rapid-freeze quench technique, and Q-10 and QH2-10 were measured with reversed-phase HPLC after extraction with petroleum ether. Ubiquinone was reduced biphasically, 8% of total Q-10 (equal to 1 mol Q-10/mol cytochrome c1), being reduced within 5 ms, and the rest, the Q-pool, at a much lower rate. The initial rapid reduction of this special Q-10 was accompanied by rapid formation of Qi and rapid reduction of a large part of the cytochrome b-562. Both semiquinone formation and reduction of b-562 showed transient kinetics due to a contribution of the reaction pathway via centre o when the iron-sulphur cluster and cytochrome c1 were oxidised. The majority of the special quinol was located at centre i, probably bound, but also at centre o some bound quinol was formed. This was visible when antimycin was present, the antimycin-insensitive bound quinol being totally sensitive to myxothiazol. Myxothiazol alone accelerated the reduction of the Q-pool via centre i, but also the equilibration of cytochrome b-562 with the Q-pool. Antimycin drastically lowered the rate of reduction of the Q-pool and additionally seemed to block the rapid electron transfer from part of the Rieske iron-sulphur cluster to cytochrome c1. It is concluded that, during the pre-steady-state, cytochrome b-562 is not in equilibrium with the Q-pool and that the rate of equilibration is probably determined by the rate of dissociation of the special bound quinol from centre i.
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PMID:Pre-steady-state reduction kinetics of QH2:cytochrome c oxidoreductase and the Q-pool: evidence for a special quinone not in rapid equilibrium with the Q-pool. 303 26

The cytochrome d-containing oxidase of oxygen-limited Escherichia coli comprises cytochromes d, cytochrome b-558 and cytochrome b-595, previously called cytochrome a1. The reaction of the fully reduced complex with oxygen involves ligand binding to the ferrous haem d to form an oxygenated species, followed by oxidation of two b-type cytochromes, whose identity is unclear. Here we report kinetic studies on cytochrome b-595 oxidation and suggest that these results, together with optical and EPR data on the oxidase complex and its reaction with oxygen, are consistent with the hypothesis that the role of cytochrome b-595 is further reduction of the oxygen bound to cytochrome d.
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PMID:Proposal that the function of the membrane-bound cytochrome a1-like haemoprotein (cytochrome b-595) in Escherichia coli is a direct electron donation to cytochrome d. 303 75

Succinate dehydrogenase was purified from the particulate fraction of Desulfobulbus. The enzyme catalyzed both fumarate reduction and succinate oxidation but the rate of fumarate reduction was 8-times less than that of succinate oxidation. Quantitative analysis showed the presence of 1 mol of covalently bound flavin and 1 mol of cytochrome b per mol of succinate dehydrogenase. The enzyme contained three subunits with molecular mass 68.5, 27.5 and 22 kDa. EPR spectroscopy indicated the presence of at least two iron sulfur clusters. 2-Heptyl-4-hydroxy-quinoline-N-oxide inhibited the electron-transfer between succinate dehydrogenase and a high redox potential cytochrome c3 from Desulfobulbus elongatus.
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PMID:Isolation of succinate dehydrogenase from Desulfobulbus elongatus, a propionate oxidizing, sulfate reducing bacterium. 358 62


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