Complexes between uncouplers of oxidative phosphorylation

Foster, M.; McLaughlin, Stuart

doi:10.1007/bf01870177

Cited by 52 publications

(29 citation statements)

References 44 publications

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“…A difference in the concentration of uncoupler produces no membrane potential when the pH (<9) is the same on both sides of the membrane. Both of these observations are due, as discussed elsewhere (Foster & McLaughlin, 1974) to 1 As discussed below, exponential relaxations in the current were noted for the three highest concentrations graphed in Fig. 2, and the conductance at these concentrations was estimated by extrapolating the current to zero time.…”

Section: Equilibrium Resultsmentioning

confidence: 56%

“…The uncoupler DTFB, like all other uncouplers which have been examined to date (e.g., LeBlanc, 1971;Borisova et al, 1974;Foster & McLaughlin, 1974) produces a Nernst potential in response to a gradient of hydrogen ions (Fig. 15).…”

Section: Discussionmentioning

confidence: 99%

“…In particular, we did not allow the value of PnA to exceed 4cm/sec. (Foster & McLaughlin (1974) have determined that the partition coefficient of DTFB into bulk decane is 1.25. We assumed that the partition coefficient of DTFB into the membrane phase would be 0.12 < kHA< 12.…”

Section: Ay=f(y+bay T)atmentioning

confidence: 99%

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The kinetic mechanism of action of an uncoupler of oxidative phosphorylation

1977

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The chemiosmotic hypothesis predicts that the mechanism by which weak acids uncouple oxidative phosphorylation in mitochondria is identical to the mechanism by which they transport hydrogen ions across artificial bilayer membranes. We report here the results of a kinetic study of uncoupler-mediated hydrogen ion transport across bilayer membranes. We made electrical relaxation measurements on black lipid membranes exposed to the substituted benzimidazole 5,6-dichloro-2-trifluoromethylbenzimidazole. The simplest model consistent with our experimental data allowed us to deduce values for adsorption coefficients and rate constants. Our major conclusions are that the back diffusion of the neutral species is the rate limiting step for the steady state transport of hydrogen ions, that both the neutral and charged forms of the uncoupler adsorb strongly to the interfaces, and that the reactions at the membrane-solution interfaces occur sufficiently rapidly for equilibrium to be maintained. Independent measurements of the adsorption coefficients of both the neutral and anionic forms of the weak acid and also of the permeability of the membrane to the neutral form agreed well with the values deduced from the kinetic study.

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Section: Equilibrium Resultsmentioning

confidence: 56%

Section: Discussionmentioning

confidence: 99%

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The kinetic mechanism of action of an uncoupler of oxidative phosphorylation

1977

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“…5). Foster and McLaughlin (1974) ha,~e shown this to be the case for the solute 5,6-dichloro-2-trifluoro-methylbenzimidazole. treatments of nonelectrolyte permeation that derived an explicit expression for the permeability coefficient in terms of these variables have made one or more of the following restrictive assumptions: that partition coefficients (or standard chemical potentials) are uniform throughout the membrane; that diffusion coefficients are uniform throughout the membrane; that the membrane is symmetrical; that interracial resistances are negligible, i.e., that there is no immediate change in solute chemical potentials on crossing either of the water/membrane interfaces; or that some other specific resistance profile or form of energy barrier to solute permeation applies through the membrane.…”

Section: Permeation Barriers In Lecithinmentioning

confidence: 88%

Interpretation of nonelectrolyte partition coefficients between dimyristoyl lecithin and water

1974

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Summary. Nonelectrolyte partition coefficients (K's) and free energies of solution (AFt's) in dimyristoyl lecithin liposomes and in bulk nonpolar solvents were compared. Individual substituent groups tend to have consistent effects on K, permitting the extraction of incremental free energies (OAF), enthalpies (OAH), and entropies (OAS) of partition and of solution. Values of the selectivity constant s and of 6riFt for the --CHzand --OH groups in lecithin suggest that partitioned solutes are mainly located in a region slightly less hydrophobic than octanol and similar to C5I-I11OH in its solvent properties. Lecithin discriminates against branched solutes more than does a bulk solvent with the same s value. Below the endothermic phase-transition temperature (i.e., when the hydrocarbon tails "freeze"), AS and dH of partition increase 10-fold, K jumps down slightly, AS and AH of solution reverse in sign from negative to positive, and the Barclay-Butler constants become more positive. Partition in lecithin and in erythrocytes is similar, except for the absence of surface charge effects in lecithin. Resistance to nonelectrolyte permeation is inhomogeneously distributed through the bilayer, and the region of maximum partition does not provide the rate-limiting barrier. An appendix derives a simple general exPression for the nonelectrolyte permeability of a membrane that may be asymmetrical, may have position-dependent partition coefficients and diffusion coefficients, and may have significant interracial resistances. This paper, the last in a series of four, analyzes nonelectrolyte average partition coefficients that were measured between water and the sucroseexcluding space of hydrated dimyristoyl lecithin liposomes and water and reported in the preceding paper (Katz & Diamond, 1974c, referred to as paper III). As discussed in the Appendix of the present paper, to attain a detailed understanding of permeation in biological membranes and thin lipid membranes will require separating the dependence of permeability coefficients on three groups of factors: those that determine, respectively, equilibrium solute concentrations in the membrane interior, solute mobilities in the membrane interior, and interracial rate processes. Partition measurements provide information about the first of these three sets of factors,

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“…There is now good experimental evidence that when a bilayer membrane is exposed to 2,4-dinitrophenol (DNP), pentachlorophenol (PCP), DTFB, or TTFB the charged permeant species is the dimer, HA2, formed between the undissociated acid, HA and its anion, A- [12,18,20,33,41,48,59]. Since the initial ohmic conductance, the conductance measured in the limit that time and voltage go to zero, is proportional to the equilibrium concentration of the HA 2 species, we discuss here the manner in which the dimer concentration depends on the pH and the total concentration of uncoupler added to the aqueous phases.…”

Section: Equilibrium Theorymentioning

confidence: 99%

Proton transport through membranes induced by weak acids: A study of two substituted benzimidazoles

Dilger

McLaughlin

1979

J. Membrain Biol.

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Summary.We report here a kinetic study of the mechanism by which the weak acid I'TFB (4,5,6,7-tetrachloro-2-trifluoromethylbenzimidazole) transports protons across phospholipid bilayer membranes. A previous kinetic study of the homologous dichloro compound, DTFB, revealed that the rate limiting step for proton translocation was the back diffusion of the neutral, HA, form of the weak acid; we conclude here that this is also the rate limiting step for proton translocation with TTFB. At high concentrations of either DTFB or TTFB the charged permeant species is an HA~ complex. The kinetic analysis and independent measurements reveal that the permeability of the membrane to HA and adsorption coefficients of A-and HA are an order of magnitude higher for TTFB than for DTFB. When either DTFB or TTFB was present in a solution where the pH was less than the pK of the weak acid, an unusual relaxation in the current was noted on application of a voltage step. The amplitude of the relaxation decreased as the voltage was increased. This relaxation is possibly due to a reorientation of the benzimidazole molecules at the membrane-solution interface. We also report experiments performed with DTFB on mitochondria. It was possible to reconcile these results with the bilayer data and, therefore, with the chemiosmotic hypothesis by postulating that the dielectric constant of the mitochondrial membrane is greater than that of a bilayer formed with decane as a solvent. To demonstrate the effect of dielectric constant on permeability, we replaced decane by 1-chlorodecane. This increased the capacitance of the artificial bilayer by a factor of two and the permeability of the bilayer to the A-form of DTFB by two orders of magnitude.In accordance with the chemiosmotic hypothesis, weak acids that transport protons across lipid bilayer membranes act as uncouplers of oxidative and photophosphorylation in mitochondria, bacteria, and chloroplasts. An understanding of the mechanism by which these weak acids transport protons across an artificial lipid bilayer system is, therefore, of biological interest. Information about the kinetic aspects of this mechanism can sometimes be obtained by perturbing the system, for example, with a voltage or temperature jump, then studying the relax-

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Complexes between uncouplers of oxidative phosphorylation

Cited by 52 publications

References 44 publications

The kinetic mechanism of action of an uncoupler of oxidative phosphorylation

The kinetic mechanism of action of an uncoupler of oxidative phosphorylation

Interpretation of nonelectrolyte partition coefficients between dimyristoyl lecithin and water

Proton transport through membranes induced by weak acids: A study of two substituted benzimidazoles

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