The oxidation-reduction kinetics of the reaction of cytochrome c1 with non-physiological redox agents

König, B.W.; Veerman, E.C.I.; Gelder, B.F. Van

doi:10.1016/0005-2728(82)90277-8

Cited by 6 publications

(2 citation statements)

References 21 publications

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“…We initially performed a large set of experiments with potassium ferricyanide to ensure a complete and irreversible oxidation of the enzyme; complete oxidation is expected since the midpoint potential of ferricyanide is much hlgher than that of the high-potential electron carriers of the complex [Z, 81. The rate of the reaction of ferricyanide with cytochrome c1 was found to be insensitive to temperature, to be unmodified by the presence of detergents and to decrease upon lowering the ionic strength of the medium; these observations are consistent with published date obtained on the oxidation of the purified cytochrome c1 by ferricyanide [35]. However, the progress curve for the oxidation of cytochrome c1 in the bcl complex does not follow a first-order process even at very high ferricyanide concentrations, contrary to observations on the oxidation of purified cytochrome c1 with this reagent [8, 351. This deviation from first-order behaviour can be ascribed to the rapid redox equilibrium between cytochrome c1 and the Rieske center The equilibrium constant K is given by the difference in midpoint potential between the Rieske iron-sulphur center and cytochrome cl, according to AE, (mV) = 59 log K .…”

Section: Oxidation Of the Uscorbate-reduced Bcl Complexsupporting

confidence: 80%

On the oxidation pathways of the mitochondrial bc₁ complex from beef heart

Esposti

Tsai

Palmer

et al. 1986

European Journal of Biochemistry

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We have investigated the oxidation of the reduced ubiquinol : cytochrome c reductase (bcl complex) isolated from beef heart mitochondria. The oxidation of cytochrome cl by both potassium ferricyanide and cytochrome c in the ascorbate-reduced bcl complex is not a first-order process. This is taken as evidence that cytochrome cI is in rapid equilibrium with the Rieske iron-sulphur center. Among the several inhibitors tested, only 5-n-undecyl-6-hydroxy-4,7-dioxobenzothiazole and stigmatellin are seen to affect this redox equilibrium between the highpotential centers of the beef heart bcl complex.The oxidation of cytochrome b by cytochrome c in both the succinate-reduced and the fully reduced bcl complex is blocked by all the inhibitors tested. This inhibition occurs simultaneously with an acceleration in the oxidation of cytochrome cl, even after extraction of the endogenous ubiquinone which is present in the bcl preparation. Almost complete extraction of ubiquinone from the bcl complex has no effect upon the rapid phase of cytochrome b oxidation, nor does it alter the inhibition of cytochrome b oxidation by the various inhibitors.The oxidation of cytochrome b by exogenous ubiquinones is stimulated by myxothiazol and partially inhibited by antimycin. However, the addition of both these inhibitors together completely blocks the oxidation of cytochrome b by quinones. In contrast, the simultaneous addition of antimycin and myxothiazol has no such synergistic effect upon the oxidation of cytochrome b by cytochrome c.Our data show that intramolecular electron transfer from cytochrome(s) b to the Rieske iron-sulphur center can take place in the bcl complex without involvement of endogenous ubiquinone-10. This electron pathway is sensitive to all the inhibitors of the enzyme. . In addition to these four intrinsic prosthetic groups, a complement of endogenous ubiquinone (mostly ubiquinone-10 in mammals) is usually found in purified preparations of the bcl complex; this quinone is present in an amount which is approximately equimolar with respect to cytochrome c1 Cytochrome c1 and the Rieske iron-sulphur center have their prosthetic groups located in a hydrophilic domain of the complex and are believed to protrude out of the cytoplasmic face of the membrane [I, 21. These redox centers react readily with membrane-impermeant redox mediators such as ferricyanide, ascorbate and the physiological electron acceptor cytochrome c [2]. The latter protein has been shown to react only with cytochrome c1 [2, 71. The 2Fe-2S cluster and c1 are in very rapid redox equilibrium [8,9] and possess a midpoint potential much higher than that of both ubiquinone and the cytochromes b [2,4,9, 101. The use of a variety of specific inhibitors of the bcl complex has been of great value in understanding the observed kinetics of electron transfer [4, 11 -161 (for a review see [12, 171). According to the concepts of the Q-cycle, antimycin, HQNO and funiculosin interact at center ' i ' , whereas a large group of inhibitors including myxothyazol, muci...

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Section: Oxidation Of the Uscorbate-reduced Bcl Complexsupporting

confidence: 80%

On the oxidation pathways of the mitochondrial bc₁ complex from beef heart

Esposti

Tsai

Palmer

et al. 1986

European Journal of Biochemistry

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“…Central to identifying the terminal ferric reductase is the ability to distinguish between the physiologically relevant ferric reductase activity of the OM compared to iron reductase activity that maybe associated with the CM for other purposes. This is important since many oxidoreductases whose physiological function is not to reduce iron have been shown to possess fortuitous iron reduction activity (19,67). Due to the relative ease which cytochromes reduce ferric chelates, it would not be surprising to find that many if not all of the multiheme proteins of DIR have ferric reductase activity.…”

Section: Discussionmentioning

confidence: 99%

Reduction of Soluble and Insoluble Iron Forms by Membrane Fractions of Shewanella oneidensis Grown under Aerobic and Anaerobic Conditions

Ruebush¹,

Brantley

Tien³

2006

Appl Environ Microbiol

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The effect of iron substrates and growth conditions on in vitro dissimilatory iron reduction by membrane fractions of Shewanella oneidensis MR-1 was characterized. Membrane fractions were separated by sucrose density gradients from cultures grown with O 2 , fumarate, and aqueous ferric citrate as the terminal electron acceptor. Marker enzyme assays and two-dimensional gel electrophoresis demonstrated the high degree of separation between the outer and cytosolic membrane. Protein expression pattern was similar between chelated iron-and fumarate-grown cultures, but dissimilar for oxygen-grown cultures. Formate-dependent ferric reductase activity was assayed with citrate-Fe 3؉ , ferrozine-Fe 3؉ , and insoluble goethite as electron acceptors. No activity was detected in aerobic cultures. For fumarate and chelated iron-grown cells, the specific activity for the reduction of soluble iron was highest in the cytosolic membrane. The reduction of ferrozine-Fe 3؉ was greater than the reduction of citrate-Fe 3؉ . With goethite, the specific activity was highest in the total membrane fraction (containing both cytosolic and outer membrane), indicating participation of the outer membrane components in electron flow. Heme protein content and specific activity for iron reduction was highest with chelated iron-grown cultures with no heme proteins in aerobically grown membrane fractions. Western blots showed that CymA, a heme protein involved in iron reduction, expression was also higher in iron-grown cultures compared to fumarate-or aerobic-grown cultures. To study these processes, it is important to use cultures grown with chelated Fe 3؉ as the electron acceptor and to assay ferric reductase activity using goethite as the substrate.In the absence of molecular oxygen, bacteria can use a variety of terminal electron acceptors for respiration. Many bacterial species have been identified that utilize insoluble metal oxides for respiration. Two such microorganisms that have received much attention are Shewanella oneidensis and Geobacter sulfurreducens (27). The genomes of both microbes have been sequenced. S. oneidensis MR-1, the focus of the present study, is highly versatile in its use of terminal electron acceptors (70). Acceptors include oxygen, fumarate, nitrate, nitrite, trimethylamine N-oxide, dimethyl sulfoxide, sulfite, thiosulfate, and elemental sulfur, as well as solid mineral oxides including hydrous ferric oxide, goethite, hematite, and manganese oxide (32,41,70) and Fe(III), Mn(IV,III), Cr(VI), and U(VI) (4,12,26,35,41,42,71).The ability of Shewanella to utilize iron oxide as the terminal electron acceptor, a process referred to as dissimilatory iron reduction (DIR), has been extensively studied. Due to the ease of genetic manipulation of Shewanella, the genes involved in DIR have been identified. These genes encode cytosolic membrane (CM), periplasmic, and outer membrane (OM) proteins, as expected for the inferred path of direct electron transfer from the cytoplasm to an insoluble extracellular substrate (7,52,59). Bio...

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Structure and Function of Respiratory Membranes in Cyanobacteria (Blue-Green Algae)

Peschek

1984

Subcellular Biochemistry

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The oxidation-reduction kinetics of the reaction of cytochrome c1 with non-physiological redox agents

Cited by 6 publications

References 21 publications

On the oxidation pathways of the mitochondrial bc₁ complex from beef heart

On the oxidation pathways of the mitochondrial bc₁ complex from beef heart

Reduction of Soluble and Insoluble Iron Forms by Membrane Fractions of Shewanella oneidensis Grown under Aerobic and Anaerobic Conditions

Structure and Function of Respiratory Membranes in Cyanobacteria (Blue-Green Algae)

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The oxidation-reduction kinetics of the reaction of cytochrome c1 with non-physiological redox agents

Cited by 6 publications

References 21 publications

On the oxidation pathways of the mitochondrial bc1 complex from beef heart

On the oxidation pathways of the mitochondrial bc1 complex from beef heart

Reduction of Soluble and Insoluble Iron Forms by Membrane Fractions of Shewanella oneidensis Grown under Aerobic and Anaerobic Conditions

Structure and Function of Respiratory Membranes in Cyanobacteria (Blue-Green Algae)

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On the oxidation pathways of the mitochondrial bc₁ complex from beef heart

On the oxidation pathways of the mitochondrial bc₁ complex from beef heart