F is a water insoluble protein with eight subunits and a transmembrane ring. The ring has a tetrameric shape with a helix-loop-helix protein that goes through conformational changes when protonated and deprotonated, pushing neighboring subunits to rotate, causing the spinning of F which then also affects conformation of F, resulting in switching of states of alpha and beta subunits. The F region of ATP synthase is a proton pore that is embedded in the mitochondrial membrane. It consists of three main subunits, a, b, and c. Six c subunits make up the rotor ring, and subunit b makes up a stalk connecting to F OSCP that prevents the αβ hexamer from rotating. Subunit a connects b to the c ring. Humans have six additional subunits, d, e, f, g, F6, and 8 (or A6L). This part of the enzyme is located in the mitochondrial inner membrane and couples proton translocation to the rotation that causes ATP synthesis in the F region.
In eukaryotes, mitochondrial F forms membrane-bending dimers. These dimers self-arrange into long rows at the end of the cristae, possibly the first step of cristae formation. An atomic model for the dimeric yeast F region was determined by cryo-EM at an overall resolution of 3.6 Å.