Proton Motive Force Calculators

0 calculators tagged with “Proton Motive Force”

Proton motive force (PMF) is the electrochemical gradient of protons (H⁺) across a biological membrane that stores potential energy used to drive ATP synthesis and other energy-requiring membrane processes. It was described by Peter Mitchell in his chemiosmotic hypothesis (Nobel Prize, 1978). The PMF has two components: a chemical gradient (ΔpH, the difference in proton concentration across the membrane) and an electrical gradient (Δψ, the membrane potential). The total PMF in millivolts equals approximately −59 × ΔpH + Δψ. ATP synthase harnesses PMF as protons flow down their electrochemical gradient.

All Calculators

No calculators found for this topic.

Mitchell Equation

PMF = Δψ − (59 × ΔpH) [in mV at 25°C]

Δψ = membrane potential (inside negative for mitochondria ≈ −180 mV); ΔpH = pH_inside − pH_outside (≈ −1 unit across inner mitochondrial membrane, contributing ~−59 mV). Total PMF ≈ −180 − 59 = −239 mV in active mitochondria. The negative sign indicates energy is stored (analogous to a charged battery).

Generating the PMF

In mitochondria: the electron transport chain (Complexes I, III, IV) pumps H⁺ from the matrix into the intermembrane space (IMS), creating: higher [H⁺] in IMS (ΔpH component) and positive charge in IMS (Δψ component). In chloroplasts: light-driven electron transport pumps H⁺ from stroma into the thylakoid lumen. In bacteria: the plasma membrane ETC pumps H⁺ outward.

ATP Synthesis

H⁺ flows back through ATP synthase (Complex V / F₁F₀-ATPase) down the electrochemical gradient, driving rotation of the c-subunit ring. Rotation changes the conformation of the β-subunits, driving ATP synthesis from ADP + Pi. Approximately 3 H⁺ are needed per ATP synthesized. Total yield: ~2.5 ATP/NADH, ~1.5 ATP/FADH₂.

Other PMF-Driven Processes

  • Active transport of metabolites (pyruvate, citrate) across inner mitochondrial membrane
  • Bacterial flagellar rotation (powered directly by PMF, not ATP)
  • Secondary active transport of nutrients in bacteria

Glossary

Proton Motive Force (PMF)
The electrochemical H⁺ gradient across a biological membrane: PMF = Δψ − 59×ΔpH (mV); stores potential energy used to drive ATP synthesis and other membrane processes.
Chemiosmosis
Peter Mitchell's model (1961) explaining how the electrochemical proton gradient (PMF) across a membrane drives ATP synthesis via ATP synthase; received Nobel Prize in 1978.
ATP Synthase (Complex V)
The F₁F₀-ATPase enzyme that uses PMF to synthesize ATP; H⁺ flow through the F₀ domain rotates the c-ring, mechanically driving ATP synthesis in the F₁ domain; ~3 H⁺ per ATP.

Frequently Asked Questions

Proton motive force (PMF) is the electrochemical gradient of H⁺ across a membrane, with two components: Δψ (membrane potential, inside negative) and ΔpH (pH difference, inside more basic). PMF = Δψ − 59×ΔpH (mV). In mitochondria, PMF ≈ −240 mV. Protons flow down this gradient through ATP synthase, and the energy released drives rotation of the enzyme's subunits — mechanically coupling proton flow to phosphorylation of ADP to ATP. About 3 H⁺ per ATP are required.

The electron transport chain (ETC) in the inner mitochondrial membrane pumps H⁺ from the matrix into the intermembrane space: Complex I pumps 4H⁺, Complex III pumps 4H⁺, and Complex IV pumps 2H⁺ per electron pair. This creates higher [H⁺] in the IMS (ΔpH) and a positive charge difference (Δψ, inside negative). NADH and FADH₂ from the citric acid cycle donate electrons to start the ETC. O₂ is the final electron acceptor, forming H₂O.

PMF = Δψ + ΔpH component. (1) Membrane potential (Δψ): charge difference across the membrane — inside mitochondrial matrix is −180 mV relative to IMS. (2) Chemical gradient (ΔpH): pH difference — matrix pH ≈ 8.0, IMS pH ≈ 7.0; ΔpH = −1.0, contributing −59 mV per pH unit. Total PMF ≈ −240 mV in active mitochondria. In chloroplasts, the ΔpH component dominates (thylakoid lumen is very acidic, pH ≈ 4–5).

Beyond ATP synthesis: (1) Bacterial flagellar motor — E. coli flagella rotate directly using PMF flux through the MotA/MotB stator complex, not ATP hydrolysis. (2) Mitochondrial carrier proteins — pyruvate, citrate, and malate/aspartate transporters use the Δψ component to drive metabolite import or export. (3) Bacterial secondary active transport — nutrient uptake (amino acids, sugars) coupled to H⁺ symport down the PMF gradient. (4) Chloroplast ATP synthesis — same F-type ATP synthase but driven by light-generated PMF across the thylakoid membrane.