Free activity

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Free activity


Free activity X [MU路m-3] is pressure divided by isomorphic force. In the chemical amount format, X is expressed in units of concentration of X [mol路L-1]. X is the local concentration in a concentration gradient. If the concentration gradient is collapsed to a boundary of zero thickness in a compartmental system, X reflects the singularity in the transition between the two phases or compartments.

Abbreviation: X [MU路m-3]


  • Gnaiger E (2020) Mitochondrial pathways and respiratory control. An introduction to OXPHOS analysis. 5th ed.
  • 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. - 禄Bioblast link芦

Isomorphic laws and isomorphic formats

In ergodynamics, the pressure in a transformation, 螖trX, is the product of free activity times force, 螖trX = X路螖trFX [mol路m-3 路 J路mol-1 = J路m-3 = Pa] (Gnaiger 1989).
Free activity has the unit concentration of the transformation-specific motive unit [MU鈭檓-3]. Therefore, pressure as the product of isomorphic force and free activity has the unique unit pascal, [Pa] = [J鈭檓-3] = [J鈭橫U-1]鈭橻MU鈭檓-3].

MitoPedia concepts: MiP concept, Ergodynamics 

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