Electron Transfer between Cardiac Cytochrome c 1 and c

Kim, Chong H.; Balny, Claude; King, Tsoo E.

doi:10.1007/978-1-4613-1941-2_57

Cited by 8 publications

(7 citation statements)

References 19 publications

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“…affecting the enzyme structure. For example, the difference redox potential between cytochrome c and cytochrome cl is positive in the isolated complex (Kim et al, 1987) but is negative in the membrane-bound form (Nicholls, 1976).…”

Section: Discussionmentioning

confidence: 99%

Steady-state kinetics of ubiquinol-cytochrome c reductase in bovine heart submitochondrial particles: diffusional effects

Fato

Cavazzoni

Castelluccio

et al. 1993

Biochemical Journal

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In an attempt to establish the relative importance of diffusional and chemical control in the reactivity of the two substrates, ubiquinol and cytochrome c, we have undertaken an extensive characterization of the steady-state kinetics of ubiquinol-cytochrome c reductase (EC 1.10.2.2) when present in open submitochondrial particles from bovine heart. The kinetic pattern follows a Ping Pong mechanism; contrary to the situation found with the isolated enzyme [Speck and Margoliash (1984) J. Biol. Chem. 259, 1064-1072, and confirmed in our laboratory], no substrate inhibition by oxidized cytochrome c was observed with the membrane-bound enzyme. Endogenous oxidized ubiquinone-10 is unable to exert product inhibition under the conditions employed. In the Ping Pong mechanism for this enzyme, the reaction scheme can be clearly divided into two parts, and the Kmin (keat/Km) value for one substrate is independent of the rate constant for the second substrate. Both ubiquinol-1 and ubiquinol-2 can be used as electron donors reacting with the enzyme from within the lipid bilayer [Fato, Castelluccio, Palmer and Lenaz (1988) Biochim. Biophys. Acta 932,[216][217][218][219][220][221][222]; the kmin values for ubiquinols, when calculated on the basis of their membranous concentrations, are significantly lower than the kmin for cytochrome c. The temperature-dependence of the kinetic parameters was investigated by titrating each of the substrates under quasi-saturating concentrations of the second substrate. Arrhenius plots of Vm.. extrapolated from both cytochrome c and ubiquinol titrations were linear, when care was taken to verify the quasi-saturating concentrations of the fixed co-substrate. The Arrhenius plots for the kmin values for both ubiquinol and cytochrome c were linear, but the activation energy was much higher for the former, particularly when calculated for ubiquinol dissolved in the lipid phase; the very low value of activation energy of the kmin for cytochrome c is strong support for diffusion control being present in the reaction of cytochrome c with the membranous enzyme. In contrast to the soluble enzyme, ubiquinone titrations of submitochondrial particles at low cytochrome c concentrations deviated from hyperbolic behaviour. Changing the medium viscosity with either poly(ethylene glycol) or sucrose had a strong effect on the cytochrome c kmin, whereas the change in the ubiquinol kmin was much smaller. From the viscosity studies the extent of diffusional control could be calculated, revealing that the reaction with cytochrome c was mostly diffusion-limited. The viscosity of the membrane was changed by incorporating cholesterol; no significant effect on the ubiquinol kmin ascribable to diffusion control could be recognized. The bulk of the studies reported here strongly suggest that ubiquinol-cytochrome c reductase is subject to diffusion control of the interaction of cytochrome c from the aqueous medium, but not of the interaction of the short-chain ubiquinols from the membrane interior. INTRODUCTIONSeveral enzy...

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Section: Discussionmentioning

confidence: 99%

Steady-state kinetics of ubiquinol-cytochrome c reductase in bovine heart submitochondrial particles: diffusional effects

Fato

Cavazzoni

Castelluccio

et al. 1993

Biochemical Journal

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“…Of these subunits, QCR6p (corresponding to subunit 8 in mammals) and QCR9p (corresponding to subunit 10) are close in the structure to the active sites of CYC1 and RISP (Iwata et al 1998;Zhang et al 1998;Lange and Hunte 2002). Although complex III can function without these two subunits, it appears that they are important for complex assembly and may modify functional interactions as well (Kim et al 1987;Schmitt and Trumpower 1991;Zara et al 2004). To gain a complete understanding of the evolution of interactions in this complex for these hybrid copepods, these additional subunits should be characterized as well.…”

Section: Significant Epistatic Interactions Between Ets Proteinsmentioning

confidence: 99%

Deleterious Epistatic Interactions Between Electron Transport System Protein-Coding Loci in the Copepod Tigriopus californicus

Willett

2006

Genetics

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The nature of epistatic interactions between genes encoding interacting proteins in hybrid organisms can have important implications for the evolution of postzygotic reproductive isolation and speciation. At this point very little is known about the fitness differences caused by specific closely interacting but evolutionarily divergent proteins in hybrids between populations or species. The intertidal copepod Tigriopus californicus provides an excellent model in which to study such interactions because the species range includes numerous genetically divergent populations that are still capable of being crossed in the laboratory. Here, the effect on fitness due to the interactions of three complex III proteins of the electron transport system in F 2 hybrid copepods resulting from crosses of a pair of divergent populations is examined. Significant deviations from Mendelian inheritance are observed for each of the three genes in F 2 hybrid adults but not in nauplii (larvae). The two-way interactions between these genes also have a significant impact upon the viability of these hybrid copepods. Dominance appears to play an important role in mediating the interactions between these loci as deviations are caused by heterozygote/homozygote deleterious interactions. These results suggest that the fitness consequences of the interactions of these three complex III-associated genes could influence reproductive isolation in this system.

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“…Any significant interference in the observed absorbance changes of cytochrome b and c1 due to the rapid reduction of cytochrome c by the bcl complex is therefore minimized by the oxidation of cytochrome c by ferricyanide. The presence of cytochrome c in the ferricyanide solution produces an order-of-magnitude increase in the observed rates of cytochrome b or c1 oxidation, due to specific reaction between the reduced enzyme and its natural electron acceptor [36]. Most of the experiments have been performed under conditions in which the rate of cytochrome c1 oxidation was at least twofold faster than that of cytochrome b oxidation, thus excluding the possibility that the interaction of the oxidants with cytochrome c1 could be significantly rate-limiting in the overall process [9, 331.…”

Section: Kinetic Measurementsmentioning

confidence: 99%

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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Electron Transfer between Cardiac Cytochrome c 1 and c

Cited by 8 publications

References 19 publications

Steady-state kinetics of ubiquinol-cytochrome c reductase in bovine heart submitochondrial particles: diffusional effects

Steady-state kinetics of ubiquinol-cytochrome c reductase in bovine heart submitochondrial particles: diffusional effects

Deleterious Epistatic Interactions Between Electron Transport System Protein-Coding Loci in the Copepod Tigriopus californicus

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

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Electron Transfer between Cardiac Cytochrome c 1 and c

Cited by 8 publications

References 19 publications

Steady-state kinetics of ubiquinol-cytochrome c reductase in bovine heart submitochondrial particles: diffusional effects

Steady-state kinetics of ubiquinol-cytochrome c reductase in bovine heart submitochondrial particles: diffusional effects

Deleterious Epistatic Interactions Between Electron Transport System Protein-Coding Loci in the Copepod Tigriopus californicus

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

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