Significance ATP, the fuel of life, is produced by a molecular machine consisting of two motors linked by a rotor. One motor generates rotation by consuming energy derived from oxidative metabolism or photosynthesis; the other uses energy transmitted by the rotor to put ATP molecules together from their building blocks ADP and phosphate. The anionic lipid cardiolipin, a component of bacterial membranes and the inner membranes of mitochondria where the machine is found, is an essential component of the enzyme. It interacts specifically, transiently, and repeatedly with the rotor of the machine, possibly lubricating its rotation or participating directly in the generation of rotation from the transmembrane proton motive force.