Chemiosmosis and proton motive force
Chemiosmosis is the coupling of electron transfer to proton pumping across a membrane, with the resulting gradient used to make ATP. The gradient is a difference in both voltage and proton concentration, and is called the protonmotive force.5 It matters because ATP synthesis depends on a membrane that stays tight to ions.1 Leaks turn stored energy into heat.3
- Earliest held
- 2013, Sousa FL, Thiergart T, Landan…
- Most discussed in
- Early bioenergetic evolution, 2013
- In the library
- 48 passages in 10 works
- Rewritten
- 2026-10-03
Coupling and leaky membranes
Sousa and colleagues (2013) noted that chemiosmotic coupling is usually considered to have arisen late. One reason is that it requires an ion-tight membrane, so that pumped ions return mostly through the ATP synthase.1 If ions return through the lipid phase of a leaky membrane, ATP synthesis is uncoupled and most of the energy spent on pumping is lost as heat.1 The authors proposed that protocells in vents with free geochemical proton gradients could adapt to a sodium-motive force while being powered by a proton-motive force.2 They treated the origin of active pumping as the larger problem that this left open.2
Efficiency and varied settings
Wallace (2013) argued that the efficiency of converting food energy to ATP differs between people. He described 'loosely coupled' individuals as burning more calories for the same ATP and producing more core body heat per ATP used.3 Preiss and colleagues (2015) addressed a different problem. Alkaliphilic bacteria face a low bulk proton-motive force at high pH, yet must still drive proton-coupled ATP synthesis. The authors say multiple strategies are hypothesized to let them circumvent this challenge.4
The respiratory chain mechanism
Brzezinski, Moe and Ädelroth (2021) described the electron current through the respiratory chain as driving proton translocation from the matrix, the negative side, to the intermembrane space, the positive side.5 Protasoni and Zeviani (2021) compared the resulting gradient to an accumulator that supplies energy to the ATP synthase.6 They also noted that complex II feeds electrons into the ubiquinol pool without directly influencing the proton gradient, because it is not a proton pump.7
When the gradient falls
Rottenberg (2023) considered cases where the electron transport system cannot generate a protonmotive force large enough to drive ATP synthesis. In those cases, ATP made by glycolysis can reverse the ATP synthase, and its hydrolysis can raise the mitochondrial membrane potential enough to keep mitochondria functional.8 If cellular ATP cannot restore the potential, mitophagy removes depolarized mitochondria. If many mitochondria in a cell depolarize, cell death by necrosis or apoptosis follows.8
Chemiosmotic coupling today requires an ion-tight membrane, so that ions pumped out return mostly through the ATP synthase, driving ATP synthesis.
Sousa FL, Thiergart T, Landan G, Nelson-Sathi S, Pereira…, 2013 · Early bioenergetic evolution · open at passage 64In the presence of free geochemical proton gradients, protocells in vents can adapt to a sodium-motive force, all the while being powered by a proton-motive force.
Sousa FL, Thiergart T, Landan G, Nelson-Sathi S, Pereira…, 2013 · Early bioenergetic evolution · open at passage 71These ‘loosely coupled’ individuals burn more calories for the same amount of ATP and thus produce more core body heat per ATP used.
Wallace DC, 2013 · Bioenergetics in human evolution and disease: implications for the origins of… · open at passage 23Multiple strategies are hypothesized to be involved in enabling alkaliphiles to circumvent the challenge of a low bulk proton-motive force energizing proton-coupled ATP synthesis at high pH.
Preiss L, Hicks DB, Suzuki S, Meier T, Krulwich TA, 2015 · Alkaliphilic Bacteria with Impact on Industrial Applications, Concepts of Early… · open at passage 1The electron current through the respiratory chain drives proton translocation across the membrane, from the inside mitochondrial matrix (negative side, n) to the outside intermembrane space (positive side, p)
Brzezinski P, Moe A, Ädelroth P, 2021 · Structure and Mechanism of Respiratory III-IV Supercomplexes in Bioenergetic… · open at passage 1The proton gradient produced during respiration, similar to an accumulator, supplies energy to operate the ATP synthase (complex V)
Protasoni M, Zeviani M, 2021 · Mitochondrial Structure and Bioenergetics in Normal and Disease Conditions · open at passage 30This process results in an increased ubiquinol pool but does not directly influence the proton gradient because CII is not a proton pump.
Protasoni M, Zeviani M, 2021 · Mitochondrial Structure and Bioenergetics in Normal and Disease Conditions · open at passage 45ATP generated by glycolysis can reverse ATP synthase, and ATP hydrolysis by ATP synthase can increase ∆Ψm to a level that is sufficient to maintain functional mitochondria
Rottenberg H, 2023 · The Reduction in the Mitochondrial Membrane Potential in Aging: The Role of the… · open at passage 7