The applicability of the donnan relation to the distribution of certain anions between mitochondria and medium

Harris, E. J.; Berent, Celia

doi:10.1016/0014-5793(70)80403-3

Cited by 23 publications

(8 citation statements)

References 6 publications

(6 reference statements)

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“…The quantitative agreement between the experimental data and the theoretical calculations constitutes a conclusive proof for the electroneutrality of the malate-citrate exchange and rules out the alternative possibility of an electrogenic malate2--&rateg-exchange, either mediated by a specific translocator or due to free distribution of the two anions according to the Gibbs-Donnan relation [37,38]. In this case the citrate-malate exchange would cause proton movement opposite to that observed experimentally.…”

Section: Discussionsupporting

confidence: 67%

The Transport of Citric‐Acid‐Cycle Intermediates in Rat‐Liver Mitochondria

Papa¹,

Lofrumento²,

Kanduc³

et al. 1971

European Journal of Biochemistry

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1.The electrical nature of the malate-citrate, malate-Pi and malate-2-oxoglutarate exchange diffusion reactions in rat liver mitochondria has been studied. The exchanges have been followed in the presence of respiratory inhibitors and oligomycin to suppress energy supply.2. The study of the effect of ionophores and uncouplers on the exchange-diffusion reactions indicates that the citrate~n-malateo,t and the malatei,-Pi, exchanges are stimulated by inducing with nigericin or with valinomycin plus carbonyl cyanide p-trifluoromethoxy phenylhydrazone (FCCP) electroneutral influx of H+ . These exchanges are unaffected by inducing electrogenic efflux of K+ from mitochondria with valinomycin. The malatei,citrate,,t exchange appears to be inhibited by electroneutral influx of H+.3. Measurement of the extra-and intramitochondrial pH shows that the malate-citrate exchange diffusion is accompanied by translocation of protons, across the mitochondrial membrane, in the same direction as citrate and the Pi-malate exchange by proton translocation in the direction of malate. Evidence is presented that the proton translocation is a direct consequence of the anion exchange. 4.It is demonstrated that the H+ : citrate and the H+ :Pi ratios determined experimentally for the malate-citrate and malate-Pi exchanges practically coincide with the theoretical ratios expected for electroneutral malate2--citrate2-and malate2--HPO:-exchanges.5. The malate-2-oxoglutarate exchange is not affected by ionophores and/or uncouplers neither it is accompanied by proton translocation across the mitochondrial membrane.6. It is concluded that the malate-citrate, malate-Pi and malate-2-oxoglutarate exchange diffusion reactions are electroneutral and that the proton translocation accompanying the malate-citrate and malate-Pi exchanges is determined by the ionization state of malic, citric and phosphoric acid. a function of the transmembrane pH difference, this being described by Equation (1) [16] where A&-and A~G are the internal and the external concentration of the anion of charge n and where A pH represents the difference between the intraand the extramitochondrial pH, and of the capacity of the mitochondria for anions. A study of the mechanism of the pH dependence of anion translocation has, however, revealed that the translocation of Pi and pyruvate [17], but not that of citric acid cycle intermediates, is directly coupled t o OHcounterflux (or H+ cotransport) [6,9]. It was therefore concluded [S] that: firstly citric-acid cycle intermediates are translocated across the mitochondrial

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Section: Discussionsupporting

confidence: 67%

The Transport of Citric‐Acid‐Cycle Intermediates in Rat‐Liver Mitochondria

Papa¹,

Lofrumento²,

Kanduc³

et al. 1971

European Journal of Biochemistry

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“…These considerations prompted us to examine, systematically, the transport of this substrate in isolated mitochondria, a topic which so far has received only limited attention [9,10]. Elucidation of the mechanism of pyruvate transport in mitochondria appears to be particularly desirable in the light of the fact that this substrate, produced by glycolysis in the cytosol, is the main physiological feeder of the citric-acid cycle in mitochondria.…”

Section: (See However [5])mentioning

confidence: 99%

“…Since undissociated carboxylic acids, but not the anionic species, are significantly lipidsoluble, it is likely that at neutral pH a free-diffusion across the membrane of weak acids takes place. Such a process might, in fact, occur at a significant rate in the case of weak monocarboxylic acids like acetate (pK, = 4.75), propionate (pK, = 4.88) and higher unsubstituted homologues, but should be negligible for relatively stronger acids like for example pyruvate which has a pK, of 2.5 [8].These considerations prompted us to examine, systematically, the transport of this substrate in isolated mitochondria, a topic which so far has received only limited attention [9,10]. Elucidation of the mechanism of pyruvate transport in mitochondria appears to be particularly desirable in the light of the fact that this substrate, produced by glycolysis in the cytosol, is the main physiological feeder of the citric-acid cycle in mitochondria.…”

mentioning

confidence: 99%

On the Mechanism of Translocation of Pyruvate and Other Monocarboxylic Acids in Rat‐Liver Mitochondria

Papa

Paradies

1974

European Journal of Biochemistry

132

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1. Pyruvate equilibrates, like other carboxylic acids, across the membrane of rat-liver mitochondria according to the transmembrane pH difference.2. Comparison of the rate of pyruvate, acetoacetate and acetate efflux from mitochondria as well as a study of the effect of mersalyl and N-ethylmaleimide on this process, show that the diffusion of pyruvic and acetoacetic acid across the mitochondrial membrane is carrier-mediated. The process might consist of pyruvate (acetoacetate) hydroxyl ion exchange-diffusion or of pyruvic acid (acetoacetic acid) uniport. On the contrary acetic acid appears to diffuse freely across the membrane.3. The initial rate of the net pyruvate uptake by rat liver mitochondria follows saturation kinetics. The increase of the external pH of the medium as well as the addition of acetoacetate inhibit competitively pyruvate uptake. Pyruvate uptake is inhibited by mersalyl and N-ethylmaleimide.4. Mitochondria1 [14C]pyruvate exchanges with unlabelled pyruvate and acetoacetate but not with other monocarboxylates, Pi and citric-acid cycle intermediates.5. The pyruvate-pyruvate and pyruvate-acetoacetate exchanges follow saturation kinetics and exhibit the same V but different K, values. Both the exchanges are inhibited by mersalyl, but not by N-ethylmaleimide.6. It is concluded that pyruvate translocation across the mitochondrial membrane is mediated by a specific transport system. Mono-, di-and tri-carboxylic substrates appear to equilibrate across the mitochondrial membrane according to the transmembrane pH difference [l, 21. This may be attained either through free diffusion of the undissociated acids or by means of carriermediated, direct or indirect, exchange-diffusion of the anionic species with hydroxyl ions (this process is practically equivalent to anion-H f symport) [l -41 (see however [5]).The movement across the mitochondrial membrane of di-and tri-carboxylic substrates has been shown to be mediated by specific translocators [3,4,6,7]. It has, on the other hand, been proposed that monocarboxylic acids diffuse freely across the mitochondrial membrane [6]. Since undissociated carboxylic acids, but not the anionic species, are significantly lipidsoluble, it is likely that at neutral pH a free-diffusion across the membrane of weak acids takes place. Such a process might, in fact, occur at a significant rate in the case of weak monocarboxylic acids like acetate (pK, = 4.75), propionate (pK, = 4.88) and higher unsubstituted homologues, but should be negligible for relatively stronger acids like for example pyruvate which has a pK, of 2.5 [8].These considerations prompted us to examine, systematically, the transport of this substrate in isolated mitochondria, a topic which so far has received only limited attention [9,10]. Elucidation of the mechanism of pyruvate transport in mitochondria appears to be particularly desirable in the light of the fact that this substrate, produced by glycolysis in the cytosol, is the main physiological feeder of the citric-acid cycle in mitochondria.In previous r...

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“…This mechanism offers a possibility of explaining why certain anions behave differently to those just mentioned [ 1 ].…”

Section: Disussionmentioning

confidence: 82%

“…Rat liver mitochondria were prepared as before [1,2]. Ratios between inside content of malate or citrate and the external concentration were measured using the 14C-labelled compounds with centrifugal separation of the mitochondria through silicone exactly as before [3 ].…”

Section: Methodsmentioning

confidence: 99%

The applicability of the donnan relation to the distribution of certain anions between mitochondria and medium

Cited by 23 publications

References 6 publications

The Transport of Citric‐Acid‐Cycle Intermediates in Rat‐Liver Mitochondria

The Transport of Citric‐Acid‐Cycle Intermediates in Rat‐Liver Mitochondria

On the Mechanism of Translocation of Pyruvate and Other Monocarboxylic Acids in Rat‐Liver Mitochondria

The relation between mitochondrial anion accumulation and the pH gradient with special reference to phosphate distribution

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