Cation Uptake as the Basis for Production of Proton Pulses by Mitochondria at the Anaerobic‐Aerobic Transition

Thomas, R C; Manger, J R; Harris, E. J.

doi:10.1111/j.1432-1033.1969.tb00789.x

Cited by 16 publications

(10 citation statements)

References 22 publications

(2 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The observed H+/site ratio in this experiment was 2.04. Identical results were obtained in the absence of added Ca2+; in this case, the compensating cation moving inward was Ca2+ which had leaked out of the mitochondria in the preceding anaerobic preincubation (20)(21)(22). In Fig.…”

supporting

confidence: 68%

Stoichiometric relationship between energy-dependent proton ejection and electron transport in mitochondria.

Brand¹,

Reynafarje²,

Lehninger³

1976

Proc. Natl. Acad. Sci. U.S.A.

108

View full text Add to dashboard Cite

The number of protons ejected during electron transport per pair of electrons per energy-conserving site (the H+/site ratio) was measured in rat liver mitochondria by three different methods under conditions in which transmembrane movements of endogenous phosphate were minimized or eliminated. (1) In the Ca2+ pulse method, between 3.5 and 4.0 molecules of 3-hydroxybutyrate and 1.75 to 2.0 Ca2+ ions were accumulated per 2 e-per site during Ca2+_ induced electron transport in the presence of rotenone, when measured under conditions in which movements of endogenous phosphate were negligible. Since entry of 3-hydroxybutyrate requires its protonation to the free acid these data correspond to an H+/site ratio of 3.5-4.0. (2) In the oxygen pulse method addition of known amounts of oxygen to anaerobic mitochondria in the presence of substrate yielded H+/site ratios of 3.0 when phosphate transport was eliminated by addition of N-ethylmaleimide or by anaerobic washing to remove endogenous phosphate. In the absence of such measures the observed H+/site ratio was 2.0. (3) In the reductant pulse method measurement of the initial steady rates of H+ ejection and oxygen consumption by mitochondria in an aerobic medium after addition of substrate gave H+/site ratios near 4.0 in the presence of N-ethylmaleimide; in the absence of the inhibitor the observed ratio was only 2.0. These and other experiments reported indicate that the values of 2.0 earlier obtained for the H+/site ratio by Mitchell and Moyle [Biochem. J. (1967) 105, 1147-11621 and others were underestimates due to the unrecognized masking of H+ ejection by movements of endogenous phosphate. The results presented here show that the H+/site ratio of mitochondrial electron transport is at least 3.0 and may be as high as 4.0.It is now widely accepted that the flow of electrons from substrate to oxygen along the respiratory chain of mitochondria is accompanied by the ejection of H+ into the suspending medium (1-4); similarly, photosynthetic electron transport in chloroplasts is accompanied by H+ absorption (1, 3-5). The electrochemical H+ gradient so generated provides the driving force for the transport of a number of mineral ions and metabolites across the mitochondrial or chloroplast membrane; it may also be the vehicle for respiratory energy transduction during oxidative and photosynthetic phosphorylation (1,3,6 measurements yielded H+/site ratios (defined as the number of H+ ejected per pair of electrons per energy-conserving site) close to 2.0 (8). Such values have also been reported by others (9-11) under similar conditions. More recently the value of 2.0 for the H+/site ratio has been brought into some question by other experimental approaches. have reported values between 3.0 and 4.0 H+ per ATP in the case of photosynthetic electron transport. Moreover, comparison of the electrochemical gradients generated across the energy-transducing membrane by electron transport with the chemical potential against which ATP can be formed from ADP and Pi indicates tha...

show abstract

supporting

confidence: 68%

Stoichiometric relationship between energy-dependent proton ejection and electron transport in mitochondria.

Brand¹,

Reynafarje²,

Lehninger³

1976

Proc. Natl. Acad. Sci. U.S.A.

108

View full text Add to dashboard Cite

show abstract

“…The actual stoichiometry of the reaction however, is, as recently shown by Thomas et al [16], 2 Ca++/-. Therefore the calculation of Mitchell and Moyle of 2 H+/ -is underestimated by a factor of 2 since there must have been 4 H+ extruded per N in exchange of 2 Ca++, plus 2 OH-exchanged with two anions.…”

Section: The Stoichiometry Of Ion Translocationmentioning

confidence: 87%

Thermodynamic and Kinetic Aspects of the Interconversion of Chemical and Osmotic Energies in Mitochondria

Azzone

Massari

1971

European Journal of Biochemistry

View full text Add to dashboard Cite

1. The conversion of osmotic energy into ATP has the following properties: a) Kf, as effluent ion, can be replaced by Rbf, whereas when H+, as influent, is replaced by other cations, the synthesis is abolished. b) Both the effluent cation and the influent H+ seem to provide energy for the synthesis.The minimal sum of ApH + A p K , compatible with the synthesis, is 2.5 units, corresponding to an osmotic potential of 3.45 kcalories per gram-ion equivalent-'. The number of ion equivalents exchanged per ATP synthesized is dependent on the dimension of the osmotic potential.c) The osmotic potential compatible with the ATP synthesis is partially affected by the phosphate potential.2. The conversion of redox into osmotic energy has the following properties:a) The number of Kf ion equivalents exchanged with protons per energy rich bond is dependent on the concentrations of H+ and K+ in the inner and outer aqueous phases, increasing up to a maximal value of 4.b) The nymber of K+ ion equivalents exchanged with protons per energy rich bond increases parallel to the increase of the amount of valinomycin, up to the value of 4.3. On the basis of available data the following thermodynamic parameters are evaluated : a) The relationship between osmotic potential and ATP synthesis. b) The relationship between redox and osmotic energy. c) The osmotic potential barrier for ion translocation. 4. A molecular mechanism for the interconversion of osmotic and chemical energies is discussed.Liver mitochondria, as well as mitochondria from other tissues, behave as a highly organized machinery for the conversion of chemical into osmotic energy and vice versa [l-71. According to the chemiosmotic scheme the translocation of protons across the membrane occurs through the operation of either the respiratory chain or the ATPase. Since the number of hydrogen carriers in the respiratory chain is limited, one of the basic tenets of the chemiosmotic hypothesis is a relatively small and constant number of protons to be translocated per oxygen atom consumed. This implies that a relatively large proton motive force is acting on the protons in order to account for the large A G required for ATP synthesis [6,7]. On the other hand the proton pump hypo-

show abstract

“…An important component of this calcium 'sink' may be the mitochondria, because it has been known for some time that they will take up divalent cations in exchange for hydrogen ions (Bartley & Amoore, 1958; Chance, 1965; see also Thomas, Manger & Harris, 1969). It is, however, probable that there are additional sites for calcium binding, since axoplasm is known to hold most of its calcium in a non-ionized state even in the presence of metabolic inhibitors (Baker, Hodgkin & Ridgway, 1971; Brinley, Tiffert, Scarpa & Mullins, 1977).…”

Section: Introductionmentioning

confidence: 99%

Effect of measured calcium chloride injections on the membrane potential and internal pH of snail neurones.

Meech¹,

Thomas²

1980

The Journal of Physiology

136

View full text Add to dashboard Cite

SUMMARY1. Ion-sensitive micro-electrodes were used to measure changes in intracellular pH (pH,) and internal chloride which resulted from the pressure injection of calcium chloride into identified Helix aspersa neurones. The-internal chloride measurement allowed the quantity of calcium chloride injected to be estimated.2. Application of the metabolic inhibitor carbonyl cyanide m-chlorophenyl hydrazone (CCmP) to a calcium-loaded cell caused an increase in the membrane potential comparable to the effect of injecting calcium itself. The effect was not observed in normal cells.3. When injected in the presence of C(mp, calcium caused a much larger and longer-lasting effect on the membrane potential than that observed in untreated cells.4. The injection of ruthenium red can increase and/or prolong the hyperpolarization caused by a given quantity of injected calcium. The pH, changes following calcium injection were biphasic and slower than normal. 5. In seven experiments, both hydrogen chloride and calcium chloride were injected into the same cell. The relative changes in pHi corresponded to the production of one hydrogen ion for each calcium ion injected. 6. The relationship between the quantity of calcium injected and the size of the induced hyperpolarization suggested that at least three calcium ions acting cooperatively are required to activate a potassium 'channel'. 7. Injection of barium chloride hyperpolarized the membrane after a delay of about 1 min. After several injections of barium the cell lost this response while retaining its normal response to calcium injection. Injection of barium also caused a slowly developing (biphasic) fall in pHi.8. We conclude that injected calcium is normally rapidly taken up by mitochondria in exchange for hydrogen ions. If this uptake process is blocked by ruthenium red or CCmP, the calcium is taken up by a second, slower, process which also releases hydrogen ions. When pre-loaded, but not otherwise, the mitochondria will release * Present address:

show abstract

Cation Uptake as the Basis for Production of Proton Pulses by Mitochondria at the Anaerobic‐Aerobic Transition

Cited by 16 publications

References 22 publications

Stoichiometric relationship between energy-dependent proton ejection and electron transport in mitochondria.

Stoichiometric relationship between energy-dependent proton ejection and electron transport in mitochondria.

Thermodynamic and Kinetic Aspects of the Interconversion of Chemical and Osmotic Energies in Mitochondria

Effect of measured calcium chloride injections on the membrane potential and internal pH of snail neurones.

Contact Info

Product

Resources

About