Proton electrochemical gradient and phosphate potential in submitochondrial particles

Gf, Azzone; Pozzan, Tullio; Viola, E.; Arslan, Paola

doi:10.1016/0005-2728(78)90037-3

Cited by 33 publications

(14 citation statements)

References 35 publications

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“…However the nature of the reaction mixture used, including Tris base plus 0.2 M sucrose, would by comparison with our own work suggest that a ApH of 50 mV or less could be expected. Thus we suspect that the main source of discrepancy between our measurements and those of Azzone et al [43] lies in the determination of A $ .…”

Section: Resultscontrasting

confidence: 38%

“…The use of 86Rbf distribution in the presence of nigericin has not been compared with distribution of weak bases and thus at present it is difficult to assess whethcr a ApH cquivalent to 50 mV found by Azzone et al [43] is a reasonablc estimate. However the nature of the reaction mixture used, including Tris base plus 0.2 M sucrose, would by comparison with our own work suggest that a ApH of 50 mV or less could be expected.…”

Section: Resultsmentioning

confidence: 99%

“…A value of 50 mV was obtained for both A $ and ApH, thus giving a total protonmotive force considerably lower than other estimates [42,44] (present work). Since it was considered that centrifugation of the submitochondrial particles did not cause any perturbation of the protonmotive force owing to possible anaerobiosis in the pelleted particles [43], alternative explanations must be sought for the low protonmotivc force. The use of I-as a pcrmeant anion for A $ determination might be inappropriate as this ion may distribute across the membrane of submitochondrial particles in the same manner as the picrate ion, which Mc Laughlin et al [45] have recently suggested will not reach electrochemical equilibrium, and would therefore underestimate A $ .…”

Section: Resultsmentioning

confidence: 99%

“…Azzone et al [43] used the distribution of 1251-and "Rb' in the presence of nigericin as indicators of A$ and ApH respectively. The distributions of these two ions between the reaction medium and the lumen of the particles were determined using a centrifugation technique to separate the particles from the medium.…”

Section: Resultsmentioning

confidence: 99%

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Clarification of Factors Influencing the Nature and Magnitude of the Protonmotive Force in Bovine Heart Submitochondrial Particles

1981

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The magnitude of the protonmotive force, and its division between pH gradient and membrane potential components has been further characterised in submitochondrial particles. In a reaction medium containing sucrose for osmotic support and 4-(2-hydroxyethyl)-l -piperazineethanesulfonate (Hepes) as buffer, with succinate as substrate, the total protonmotive force reached a maximum value of 245 mV. The presence of CI-enhanced the pH gradient with a partial but not fully compensating decrease in the membrane potential. When submitochondrial particles were suspended in a medium of low osmolarity consisting of phosphoric acid neutralised with Tris, again with succinate as substrate, the protonmotive force was lower and did not exceed 185 mV, and the pH gradient coniponent was equivalent to 25 mV or less.The final phosphorylation potential, AC,, maintained by the particles was higher in the phosphate/Tris medium (46-47.7 kJ mol-.') than in the sucrose/ Hepes/KCI medium (43.7 kJ rnol -'). Thus, comparison of the phosphorylation potential with the protonmotivc force would suggest that the mechanistic stoichiometry H'/ATP (H+ translocated per molecule of ATP synthesied) for the ATPase enzyme is 3 in the former medium and 2 in the latter, which might be taken to indicate two different types of mechanism required for ATP synthesis. However it is questioned whether a comparison of the protonmotive force with AC, in terms of equilibrium thermodynamics ought not to be complemented by analysis in terms of linear non-equilibrium thermodynamics. The latter treatment shows that it is possible to estimate only a value for the product of a phenomenological stoichiometry and the degree of coupling, which can be variable, but not the mechanistic stoichiometry. This treatment can also rationalise the observation of the higher AG, in reaction conditions where the lower values for Ap are estimated. Irrespective of possible explanations, the data show how an unprejudiced choice of reaction conditions can lead to different conclusions about the relationship between the phosphorylation potential and the protonmotive force.Although the acceptance of a chemiosmotic mechanism for membrane-energy transductions is widespread, the problem of quantitatively determining the thermodynamic capacity of the intermediate in chemiosmosis, the protonmotive force, remains.In previous experiments with submitochondrial particles we encountered the somewhat unexpected result that a higher protonmotive force was detected in a reaction mixture that contained sucrose, Hepes and KC1, compared with a reaction mixture that contained phosphoric acid neutralised with Tris base as the main ingredient [1,2]. The lower value for the protonmotive force found in the Pi/Tris medium was not paralleled by a lower value for the phosphorylation potential, so that on a thermodynamic basis a greater number of protons was apparently required per molecule of ATP synthesised in the P,/Tris medium [I], and also the lower protonmotive force could not be attributed to an uncouplingeffe...

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Section: Resultscontrasting

confidence: 38%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Clarification of Factors Influencing the Nature and Magnitude of the Protonmotive Force in Bovine Heart Submitochondrial Particles

1981

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“…Thexe include direct interactions between ATP synthetase and components of the respiratory chain [14] such as cytochrome oxidase [15], titrations of the protonmotive force and phosphorylation in a variety of experimental conditions [16,17], and the enhanced depression by protonophorous uncoupling agents of the protonmotive force [18] or phosphorylation [19] in comparison with nigericin plus valinomycin in the presence of K'.…”

Section: Effect Of Energisation Upon Ihe Distribution Qf Tiimentioning

confidence: 99%

Uptake of Thallous Ions by Mitochondria is Stimulated by Nonactin but not by Respiration Alone

Skulskii¹,

Saris

Savina³

et al. 1981

Eur J Biochem

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Nonrespiring rat-liver mitochondria swell in media containing high concentrations of thallous nitrate, indicating passive penetration of Tl'. This swelling could be further stimulated by 10 nM or more nonactin while even 1 pM valinomycin was without effect. Nonactin was also much more potent than valinomycin in stimulating swelling of respiring mitochondria in the presence of thallous acetate. It is evident that nonactin acts as a potent ionophore of T1' able to promote both the passive and energized uptake of T1' in mitochondria.The distribution of TI+, present in trace concentrations below 1 mM, was measured during energisation by respiration both in the presence and absence of ionophores. Respiration induced net uptake of T1+ only in the presence of ionophores, though T1+ as a permeant cation was expected to sense respiration-induced changes in the membrane potential. The data may be interpreted as indicating that no transmembrane potential is formed upon energisation, but localized fields, which are able to interact with the lipophilic ionophore complexes of TI +, but not with the hydrophilic cation Tl'. This interpretation is valid only if thermodynamic equilibrium has been reached.

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Transport of Ions and the Membrane Potential of Mitochondria

Tedeschi

1982

Membranes and Transport

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Proton electrochemical gradient and phosphate potential in submitochondrial particles

Cited by 33 publications

References 35 publications

Clarification of Factors Influencing the Nature and Magnitude of the Protonmotive Force in Bovine Heart Submitochondrial Particles

Clarification of Factors Influencing the Nature and Magnitude of the Protonmotive Force in Bovine Heart Submitochondrial Particles

Uptake of Thallous Ions by Mitochondria is Stimulated by Nonactin but not by Respiration Alone

Transport of Ions and the Membrane Potential of Mitochondria

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