Living cells depend on an efficient transformation of the energy derived from light and foodstuff into the chemical energy of adenosine triphosphate (ATP), the universal energy carrier. The enzyme that facilitates this type of energy conversion in bacteria, chloroplast and mitochondria is ATP synthase, a complex of two molecular motors mechanically coupled by a common central stalk.

The membrane unit F_o converts the transmembrane electrochemical potential into mechanical energy that drives the central stalk rotation inside the solvent-exposed F₁ unit. The rotation causes cyclic conformational changes in the F₁ unit catalytic sites, which drive ATP synthesis (the "binding change" mechanism). ATP synthase can also operate in the reverse direction, utilizing the energy released in the process of ATP hydrolysis to pump protons across the membrane.

Several studies of this system are underway: