Gnaiger 2018 EBEC2018
The protonmotive force under pressure: an isomorphic analysis. |
Link: EBEC2018
Gnaiger E (2018)
Event: EBEC2018 Budapest HU
‘.. the sum of the electrical pressure difference and the osmotic pressure difference (i.e. the electrochemical potential difference) of protons’ [1] links to non-ohmic flux-force relationships between proton leak and protonmotive force (pmf). This is experimentally established, has direct consequences on mitochondrial physiology, but is theoretically little understood. Here I distinguish pressure from potential differences (diffusion: ΔμH+ or ΔdFH+; electric: ΔΨ or ΔelF), to explain non-ohmic flux-force relationships on the basis of four thermodynamic theorems. (1) Einstein’s diffusion equation explains the concentration gradient (dc/dz) in Fick’s law as the product of chemical potential gradient (the vector force and resistance determine the velocity, v, of a particle) and local concentration, c. This yields the chemical pressure gradient (van’t Hoff equation): ddΠ/dz = RT∙dc/dz. Flux is the product of v and c; c varies with force. Therefore, flux-force relationships are non-linear. (2) The pmf is not a vector force; the gradient is replaced by a pressure difference, and local concentration by a distribution function or free activity, α. Flux is a function of α and force, Jd = b∙α∙ΔdFB = -b∙ΔdΠB. (3) At ΔelF = -ΔdFH+, the diffusion pressure of protons, ΔdΠH+ = RT∙ΔcH+ [Pa=J∙m-3] is balanced by electric pressure, maintained by counterions of H+. Diffusional and electric pressures are isomorphic, additive, and yield protonmotive pressure (pmp). (4) The dependence of proton leak on pmf varies with ΔelF versus ΔdFH+, in agreement with experimental evidence. The flux-force relationship is concave at high mitochondrial volume fractions, but near-exponential at small mt-matrix volume ratios. Linear flux-pmp relationships imply a near-exponential dependence of the proton leak on the pmf.
• Bioblast editor: Kandolf G, Gnaiger E
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Affiliations
- D. Swarovski Research Lab, Dept Visceral, Transplant Thoracic Surgery, Medical Univ Innsbruck
- Oroboros Instruments
- Innsbruck, Austria. - [email protected]
Reference
- Mitchell P (1966) Chemiosmotic coupling in oxidative and photosynthetic phosphorylation. Glynn Research, Bodmin, Biochim Biophys Acta Bioenergetics 1807:1507-38