ATP Synthase is responsible for making ATP at the end of the electron transport chain. The enzyme consists of two major regions; F0 which sits across the membrane, and F1 that projects into the matrix of the mitochondria. The F0 region is where proteins enter via 12 c-subunits that rotate as they associate with protons from the intermembrane space of the mitochondria. One complete turn of F0 results in a proton being released into the matrix. The rotation of F0 causes the gamma (γ) unit to rotate. This rotation causes conformational changes in the α and β subunits of F1.
F1 is the catalytic region of the enzyme. This is where ATP is produced. Its α and β subunits form a hexamer (6 parts). The conformational changes caused by the rotation of the γ unit converts the α subunit from the open, to loose, to tight, conformation. In the open form, ADP and Pi enters the F0 region. In the loose form, the reactants are locked in place but do not react. In the tight form, the reactants come close enough to react, producing ATP which is then released.