Chemical and Chemiosmotic Aspects of Electron Transport-Linked Phosphorylation

Ernster, Lars

doi:10.1146/annurev.bi.46.070177.005001

Cited by 51 publications

(8 citation statements)

References 39 publications

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“…23 A and B), that cytochrome oxidase translocated almost exactly 2 electrons inwards through the membrane per 0 atom reduced from the inner aqueous phase; that is to say, it had a +e-/O ratio near 2 but it had a c H + / O ratio of zero [49] (and see [48]), contrary to reports by Wikstrom and colleagues [129]. These observations seem to us to leave very little doubt that the c H + / O ratios corresponding to 2 per effective redox loop, measured by our 02-pulse method, are not spurious underestimates, as Lehninger and colleagues (see [127]) have persuasively suggested, and as other authoritative workers, including Boyer [130], Chance [131], Ernster [132], Klingenberg [91,92], David Nicholls [133], Skulachev [134], Slater [47] and Wikstrom [129], have tended to accept. On the other hand, our conclusion that the +-H+/2e-ratio is 2 per effective redox loop has been largely corroborated by respiratory pulse measurements (see [12,42,43,45]), with whole mitochondria and bacteria, for example, in the laboratories of Chap-pel1 [135], Garland [136-1391, Jones [140-1431 and Papa [145] (but see [146]), with sub-mitochondria1 vesicles, in the laboratories of Hinkle [147] and Papa [145], and with liposomes inlaid with respiratory chain complexes, in the laboratories of Hinkle and others (see [148] When I first drew attention to this remarkable effect some years ago [125], I suggested that N-ethylmaleimide treatment favoured the involvement of the complete respiratory chain from NADPH to oxygen, because Jennifer Moyle and I had found that Nethylmaleimide largely inactivated several NAD-linked enzymes, and also inhibited succinate dehydrogenase, but did not inhibit the NADP-linked isocitrate dehydrogenase or the NADH oxidase or NAD(P) transhydrogenase [126].…”

Section: Chemiosmotic Stoicheiometrycontrasting

confidence: 47%

Compartmentation and Communication in Living Systems. Ligand Conduction: a General Catalytic Principle in Chemical, Osmotic and Chemiosmotic Reaction Systems

Mitchell

1979

European Journal of Biochemistry

350

132

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Chemical reactions, like osmotic reactions, are transport processes when looked at in detail. Chemical catalysis by enzymes or catalytic carriers, and osmotic catalysis by porters, may be conceived as occurring by specific ligand‐conduction mechanisms. In chemiosmotic reaction systems, the pathways of specific ligand conduction are spatially orientated through anisotropic enzyme and catalytic carrier complexes in which the reactions of chemical group transfer occur as vectorial diffusion processes of group translocation down gradients of group potential that represent real spatially‐directed fields of chemical force. Thus, it is easier to explain biochemistry in terms of transport than it is to explain transport in terms of biochemistry.

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Section: Chemiosmotic Stoicheiometrycontrasting

confidence: 47%

Compartmentation and Communication in Living Systems. Ligand Conduction: a General Catalytic Principle in Chemical, Osmotic and Chemiosmotic Reaction Systems

Mitchell

1979

European Journal of Biochemistry

350

132

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“…An indirect mechanism implies that ATP hydrolysis and proton transport do not share an intermediate step (8). Instead, there is a distinct coupling mechanism linking the two processes.…”

Section: Discussionmentioning

confidence: 99%

Effects of Temperature on the Coupled Activities of the Vanadate-Sensitive Proton Pump from Maize Root Microsomes

Bräuer

Loper²,

Schubert³

et al. 1991

Plant Physiol.

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The mechanism by which proton transport is coupled to ATP hydrolysis by vanadate-sensitive pumps is poorly understood. The effects of temperature on the activities of the vanadatesensitive ATPase from maize (Zea mays) roots were assessed to provide insight into the coupling mechanism. The initial rate of proton transport had a bell-shaped dependence on temperature with an optimal range between 20 and 300C. However, the rate of vanadate-sensitive ATP hydrolysis increased as the temperature was raised from 4 to 430C. The differential sensitivity of proton transport to temperatures above 300C was also observed when the ATPase was reconstituted into dioleoylphosphatidylcholine vesicles. Inhibition of proton transport with temperatures above 300C was associated with higher rates of proton leakage from the membranes. In addition, proton transport was more inhibited than ATP hydrolysis at temperatures below 100C. Reduced rates of proton transport at lower temperatures were not associated with higher rate of proton conductivity across the membranes. Therefore, the preferential inhibition of proton transport at temperatures below 100C may reflect an effect of temperature on the coupling between proton transport and ATP hydrolysis within the vanadate-sensitive ATPase.Plant cells contain two predominant classes ofproton translocating ATPase which energize solute transport (5,16 With vacuolar-type ATPase from maize (Zea mays) root tonoplast vesicles, the temperature dependence of the proton transport differed from that ofATP hydrolysis (17). The initial rate of proton transport declined as the temperature was increased above 25°C, whereas the rate of ATP hydrolysis by the pump continued to increase. These results supported the hypothesis that proton transport and ATP hydrolysis by the vacuolar ATPase were indirectly coupled. In this paper, the nature of the coupling mechanism of the plasma membranetype ATPase from maize root has been investigated in a similar manner by examining the temperature dependence of proton transport and ATP hydrolysis. MATERIALS AND METHODS Preparation of Membrane VesiclesMaize seedlings (Zea mays L., cv WF9 x Mo 17) were grown on filter paper moistened with CaCl2 (13). KI-washed microsomes were prepared from 3-d-old roots as described previously (3). The ATPase in these microsomes were reconstituted into di-18:1 PC' liposomes by a detergent dilution protocol using deoxycholate as described previously (3), using a lipid to protein ratio of 20 to 1 by weight. Protein concentration was determined by a modification of the Lowry method after precipitation by TCA in the presence of deoxycholate (2). Proton Transport and ATP Hydrolysis AssaysProton transport was followed primarily by changes in the absorbance of AO at 492.5 nm as described by de Michelis et al. (5). Assays were conducted with Beckman DU-702 spectrophotometer equipped with a thermoregulated cell holder attached to a circulating water bath. Temperature in a cuvette containing assay medium adjacent to the sample was monitored. Typi...

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“…In these experiments (Hitchens & Kell, 1982a) we carried out double-inhibitor titrations (see Baum et al, 1971;Ernster, 1977;Kell et al, 1978;Storey & Lee, 1981;Venturoli & Melandri, 1982), in which photophosphorylation by chromatophores of Rhodopseudomonas capsulata N22, incubated under conditions of saturating illumination, was partially decreased by the addition of the covalent H+-ATP synthase inhibitor DCCD, and then titrated with the electron-transport inhibitor antimycin A. We were able to conclude (Hitchens & Kell, 1982a;cf.…”

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confidence: 97%

“…* To whom correspondence and requests for reprints should be addressed. phore membrane, as in macroscopic versions of the chemiosmotic hypothesis of membrane energycoupling processes (see, e.g., Mitchell, 1966Mitchell, , 1979aNicholls, 1982), or whether there exist more localized and direct free-energy-transferring interactions between electron transport and H+-ATP synthase complexes in these and other energycoupling membranes (see, e.g., Ernster, 1977;Del Valle-Tascon et al, 1978;Rottenberg, 1978;Williams, 1978;Kell, 1979;Petty & Jackson, 1979;Fillingame, 1980;Melandri et al, 1980Melandri et al, , 1981Baccarini-Melandri et al, 1981;Conover & Azzone, 1981;Malpress, 1981;Schuurmans et al, 1981;Storey & Lee, 1981;Westerhoff et al, 1981;Venturoli & Melandri, 1981).…”

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confidence: 99%

Uncouplers can shuttle between localized energy-coupling sites during photophosphorylation by chromatophores of Rhodopseudomonas capsulata N22

Hitchens¹,

Kell²

1983

Biochemical Journal

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Two models of the action of uncoupler molecules in inhibiting photophosphorylation in bacterial chromatophores are considered: either uncoupler molecules shuttle rapidly between energy-coupling sites, or uncoupler molecules that are bound to particular sites in the chromatophores for a time that is comparable with the turnover time of the photophosphorylation apparatus may uncouple by a co-operative "substoichiometric' mechanism. It is found that the titre of uncoupler necessary to cause complete uncoupling is lowered if the rate of photophosphorylation is initially decreased by partially restricting electron flow with an appropriate titre of antimycin A. This result indicates that uncoupler molecules shuttle rapidly between energy coupling in which the energized intermediate between electron transport and phosphorylation is delocalized over the entire chromatophore membrane and those in which it is not. If the rate of photophosphorylation is partially restricted with the covalent H+-translocating ATP synthase inhibitor dicyclohexylcarbodi-imide, the titre of uncoupler necessary to effect complete inhibition of photophosphorylation is also decreased relative to that in which the covalent H+-ATP synthase inhibitor is absent. This important result appears to be inconsistent with models of electron-transport phosphorylation in which the "energized state' of the chromatophore membrane that is set up by electron transport and utilized in photophosphorylation is delocalized over the entire chromatophore membrane.

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Chemical and Chemiosmotic Aspects of Electron Transport-Linked Phosphorylation

Cited by 51 publications

References 39 publications

Compartmentation and Communication in Living Systems. Ligand Conduction: a General Catalytic Principle in Chemical, Osmotic and Chemiosmotic Reaction Systems

Compartmentation and Communication in Living Systems. Ligand Conduction: a General Catalytic Principle in Chemical, Osmotic and Chemiosmotic Reaction Systems

Effects of Temperature on the Coupled Activities of the Vanadate-Sensitive Proton Pump from Maize Root Microsomes

Uncouplers can shuttle between localized energy-coupling sites during photophosphorylation by chromatophores of Rhodopseudomonas capsulata N22

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