Operational definition
Energy-coupling mechanism.
The use of an electrochemical ion gradient across a selectively permeable membrane to couple an energy-releasing process to an energy-requiring process.
A chemiosmotic system requires:
- a membrane;
- unequal ion electrochemical potentials across that membrane;
- controlled ion permeability;
- machinery that creates or consumes the gradient.
The principal ions are usually protons or sodium ions.
24.1 Proton motive force
Δ p=Δψ-(2.303RT / F)Δ pH
Its components are:
- electrical membrane potential
- chemical proton gradient
24.2 Sodium motive force
A sodium electrochemical gradient drives:
- ATP production
- transport
- motility
- other cellular work
24.3 Mixed ion systems
Some organisms use both proton- and sodium-coupled systems.
24.4 ATP synthase coupling
ion motive force → ATP synthase rotation → ATP
Proton motive force and sodium motive force are therefore conserved intracellular energetic states, not equivalent primary environmental trophic sources. (PubMed Central (PMC))