Measurement of the proton-motive stoichiometry of the respiratory chain of rat liver mitochondria: the effect of N-ethylmaleimide

Mitchell, Roy; Ic, West; Moody, A. John; Mitchell, Peter

doi:10.1016/0005-2728(86)90029-0

Cited by 15 publications

(6 citation statements)

References 17 publications

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“…It is difficult, however, to assess the contributions of NAD-linked and NADPlinked isocitrate oxidation in this system [30]. Moreover, these estimates are subject to potential interference by other proton-coupled ion movements across the mitochondrial membrane [31,32].…”

Section: Thermodynamics Of Energy-linked Transhydrogenasementioning

confidence: 99%

“…On the basis of an ATPase stoichiometry of 3 protons/ATP, these data suggest a minimum stoichiometry of one H+/ 2e-for transhydrogenase. This approach is probably less subject to interfering ion movements than earlier methods and is less dependent on corrections for variable AAH+ (see [32,35] for a discussion of the merits of comparable approaches to stoichiometry measurements during electron transport).…”

Section: Thermodynamics Of Energy-linked Transhydrogenasementioning

confidence: 99%

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Physiological roles of nicotinamide nucleotide transhydrogenase

Hoek

Rydström

1988

Biochemical Journal

328

210

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From the foregoing considerations, the energy-linked transhydrogenase reaction emerges as a powerful and flexible element in the network of redox and energy interrelationships that integrate mitochondrial and cytosolic metabolism. Its thermodynamic features make it possible for the reaction to respond readily to challenges, either on the side of NADPH utilization or on the side of energy depletion. Yet, the kinetic features are designed to prevent a wasteful input of energy when other sources of reducing equivalents to NADP are available, or to deplete the redox potential of NADPH in other than emergency conditions. By virtue of these characteristics, the energy-linked transhydrogenase can act as an effective buffer system, guarding against an excessive depletion of NADPH, preventing uncontrolled changes in key metabolites associated with NADP-dependent enzymes and calling on the supply of reducing equivalents from NAD-linked substrates only under conditions of high demand for NADPH. At the same time, it can provide an emergency protection against a depletion of energy, especially in situations of anoxia where a supply of reducing equivalents through NADP-linked substrates can be maintained. The flexibility of this design makes it possible that the functions of the energy-linked transhydrogenase vary from one tissue to another and are readily adjustable to different metabolic conditions.

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Section: Thermodynamics Of Energy-linked Transhydrogenasementioning

confidence: 99%

Section: Thermodynamics Of Energy-linked Transhydrogenasementioning

confidence: 99%

Physiological roles of nicotinamide nucleotide transhydrogenase

Hoek

Rydström

1988

Biochemical Journal

328

210

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“…However, efforts to establish the existence of the second oxygen-reducing centre, required by the O loop and O cycle mechanisms, have not so far yielded encouraging results. Consequently, I have thought it wise to continue to prospect for conceivable direct mechanisms of coupling between electron transfer and net proton translocation in cyto-chrome oxidase, giving a stoichiometry of one proton translocated per electron transferred as originally observed by Wikstr6m (see [1,[11][12][13][14]), in case a more promising mechanistic hypothesis might be found.…”

Section: Introductionmentioning

confidence: 99%

A new redox loop formality involving metal‐catalysed hydroxide‐ion translocation A hypothetical Cu loop mechanism for cytochrome oxidase

Mitchell

1987

FEBS Letters

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A new hypothetical type of redox loop is described, which translocates hydroxide ions instead of protons. Conventional protonmotive redox loops use carriers of protons with electrons (e.g. QH2/Q systems) to couple electron transfer to the translocation of protons. The putative hydroxidemotive redox loop uses carriers ' of hydroxide ions against electrons (e.g. transition-metal centres) to couple electron transfer to the translocation of hydroxide ions. This simple idea leads to the proposal of a hydroxidemotive Cu loop mechanism that may possibly be applicable to the CUA or CuB centre of cytochrome oxidase, and might thus account for the coupling of electron transfer to net proton translocation in that osmoenzyme.

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“…The Q cycle hypothesis has satisfactorily addressed many lines of experimental observations, such as the oxidant-induced cytochrome b reduction (Erecinska et al 1972;Wikstrom and Berden 1972), the existence of antimycin-sensitive and -insensitive transient semiquinone radicals (Yu et al 1978;Ohnishi and Trumpower 1980), and stoichiometry of two protons per electron transferred (Brand et al 1976;Mitchell et al 1986). A critical requirement of the Q cycle hypothesis is the bifurcated ET at the Q o site, which was implicitly assumed and was never experimentally proven.…”

Section: [Traduit Par La Rédaction]mentioning

confidence: 98%

A novel electron transfer mechanism suggested by crystallographic studies of mitochondrial cytochrome bc1 complex

Xia¹,

Kim²,

Yu³

et al. 1998

Biochem. Cell Biol.

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The crystal structure of bovine mitochondrial cytochrome bc1 complex, an integral membrane protein complex of 11 different subunits with a total molecular mass of 242 kDa, demonstrated a tightly associated dimer consisting of three major regions: a matrix region primarily made of subunits core1, core2, 6, and 9; a transmembrane-helix region of 26 helices in the dimer contributed by cytochrome b, cytochrome c1, the Rieske iron-sulfur protein (ISP), subunits 7, 10, and 11; and an intermembrane-space region composed of extramembrane domains of ISP, cytochrome c1, and subunit 8. The structure also revealed the positions of and distances between irons of prosthetic groups, and two symmetry related cavities in the transmembrane-helix region upon dimerization of the bc1 complex. Extensive crystallographic studies on crystals of bc1 complexed with inhibitors of electron transfer identified binding pockets for both Qo and Qi site inhibitors. Discrete binding sites for subtypes of Qo site inhibitors have been mapped onto the Qo binding pocket, and bindings of different subtypes of Qo site inhibitors are capable of inducing dramatic conformational changes in the extramembrane domain of ISP. A novel electron transfer mechanism for the bc1 complex consistent with crystallographic observations is discussed.

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Measurement of the proton-motive stoichiometry of the respiratory chain of rat liver mitochondria: the effect of N-ethylmaleimide

Cited by 15 publications

References 17 publications

Physiological roles of nicotinamide nucleotide transhydrogenase

Physiological roles of nicotinamide nucleotide transhydrogenase

A new redox loop formality involving metal‐catalysed hydroxide‐ion translocation A hypothetical Cu loop mechanism for cytochrome oxidase

A novel electron transfer mechanism suggested by crystallographic studies of mitochondrial cytochrome bc1 complex

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