ATP synthase is a complex transmembrane protein that utilizes potential energy stored via the electrochemical gradient to synthesize ATP. This protein acts as a tiny generator, rotated by the force of the hydrogen ions diffusing through it via chemiosmosis (see figure below). The motion of the protons makes the stalk subunit of ATP synthase rotate, causing the active site of the enzyme domain to change shape. This ultimately results in the phosphorylation of ADP, turning it into ATP in a process called oxidative phosphorylation.
ATP synthase is a protein complex that uses the proton gradient in the inner mitochondrial membrane to produce ATP.