Animation showing the enzyme ATP synthase producing ATP adenosine triphosphate, the carrier of metabolic energy in cells. ATP synthase is an enzyme found in the inner membrane beige of mitochondria. It projects from the membrane into the mitochondrial matrix, which is enclosed by the membrane. The membrane_bound part called Fo comprises a proton pump grey tube, right connected to a rotating portion ridged tube. As protons blue balls pass through the membrane, they cause the protein to rotate, a motion which is transmitted to the matrix part of the enzyme called F1 by the blue gamma subunit. This rotates a hexagonal array of alternating three alpha yellow and beta orange subunits. The alpha and beta subunits have three states. The first is open and admits ADP adenosine diphosphate and organic phosphate Pi, which are bound after a third of a turn, then another third of a turn forces the ADP and Pi together, forming ATP. The final third of a turn returns the state to open, releasing the ATP and accepting more ADP and Pi. This is shown by three protons passing through the channel for every molecule of ATP made.