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Gnaiger 2018 EBEC2018

From Bioblast
The protonmotive force under pressure: an isomorphic analysis.

Link: EBEC2018

Gnaiger E (2018)

Event: EBEC2018 Budapest HU

ā€˜.. the sum of the electrical pressure difference and the osmotic pressure difference (i.e. the electrochemical potential difference) of protonsā€™ [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 [2,3]. Here I distinguish pressure from potential differences (diffusion: Ī”Ī¼H+ or Ī”dFH+; electric: Ī”ĪØ or Ī”elF), to explain non-ohmic flux-force relationships on the basis of four thermodynamic theorems. (1) Einsteinā€™s diffusion equation [4] explains the concentration gradient (dc/dz) in Fickā€™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 (vanā€™t Hoff): ddĪ /dz = RTāˆ™dc/dz. Flux [5] 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, Ī±. Flux is a function of Ī± and force, Jd = bāˆ™Ī±āˆ™Ī”dFB = -bāˆ™Ī”dĪ B [6]. (3) At Ī”elF = -Ī”dFH+, the diffusion pressure of protons, Ī”dĪ H+ = RTāˆ™Ī”cH+ [Pa=Jāˆ™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 Ī”elF versus Ī”dFH+, 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.


ā€¢ Bioblast editor: Gnaiger E ā€¢ O2k-Network Lab: AT Innsbruck Gnaiger E


Affiliations

  1. D. Swarovski Research Lab, Dept Visceral, Transplant Thoracic Surgery, Medical Univ Innsbruck
  2. Oroboros Instruments
Innsbruck, Austria. - [email protected]

References

  1. Mitchell P (1966) Chemiosmotic coupling in oxidative and photosynthetic phosphorylation. Glynn Research, Bodmin. Biochim Biophys Acta Bioenergetics 1807:1507-38. - Ā»Bioblast linkĀ«
  2. Garlid KD, Beavis AD, Ratkje SK (1989) On the nature of ion leaks in energy-transducing membranes. Biochim Biophys Acta 976:109-20. - Ā»Bioblast linkĀ«
  3. Beard DA (2005) A biophysical model of the mitochondrial respiratory system and oxidative phosphorylation. PLOS Comput Biol 1(4):e36. - Ā»Bioblast linkĀ«
  4. Einstein A (1905) Ɯber die von der molekularkinetischen Theorie der WƤrme geforderte Bewegung von in ruhenden FlĆ¼ssigkeiten suspendierten Teilchen. Ann Physik 4, XVII:549-60. - Ā»Bioblast linkĀ«
  5. Gnaiger E (1993) Nonequilibrium thermodynamics of energy transformations. Pure Appl Chem 65:1983-2002. - Ā»Bioblast linkĀ«
  6. Gnaiger E (1989) Mitochondrial respiratory control: energetics, kinetics and efficiency. In: Energy transformations in cells and organisms. Wieser W, Gnaiger E (eds), Thieme, Stuttgart:6-17. - Ā»Bioblast linkĀ«


Labels: MiParea: Respiration 




Regulation: Flux control, Ion;substrate transport, mt-Membrane potential  Coupling state: LEAK 


Event: Oral  MitoEAGLE