ATP synthase is a complex which makes use of the proton potential created by the action of the electron transport chain in mitochondria.It transports a proton down the gradient and uses the energy to complete the phosphorylation of ADP to ATP.o part of its action is like a molecular motor. In the electron transport chain of photosynthesis, the ATP synthase complex accomplishes the phosphorylation of ADP to ATP, providing part of the energy for subsequent biosynthesis through the Calvin cycle.