ATP synthase: motoring to the finish line.

Protonmotive force produced by the electron transport chain is harnessed by the rotary molecular nanomotor ATP synthase to generate ATP. In this issue of Cell, Adachi et al. (2007), in a dazzling display of technical sophistication, now disentangle the coupling between the mechanical force generated by rotation of the ATP synthase subunits and the chemical reactions that occur simultaneously at the enzyme's three catalytic sites.