Protonmotivkraft

Protonmotivkraft, or proton motive force (PMF) in English, is the energy stored in the electrochemical gradient of protons across a biological membrane. It arises when proton pumps move H+ ions from one side of the membrane to the other, creating both a proton concentration difference and an electrical potential.

PMF has two components: a chemical gradient (ΔpH) and an electrical gradient (Δψ). The overall force can be described by pmf = Δψ − (2.303 RT/F) ΔpH, with a common 25°C approximation of pmf ≈ Δψ − 0.059 ΔpH in volts. The typical magnitude of PMF is on the order of 100–200 millivolts under physiological conditions.

PMF is generated in mitochondria during respiration, in chloroplasts and cyanobacteria during photosynthesis, and in many bacteria across the plasma membrane. The stored energy is used by the enzyme complex ATP synthase (F0F1-ATP synthase) to drive ATP production as protons flow back across the membrane. In addition to ATP synthesis, PMF powers various energy-dependent processes such as active transport and, in some organisms, the rotation of flagella.

Significance and applications of PMF lie at the core of chemiosmotic theory, explaining how energy from redox reactions is converted into ATP. Disruption of proton gradients can impair cellular energy metabolism, making PMF a central concept in bioenergetics, microbiology, and physiology.