In the last step, the beta subunit is converted to the open form and ATP is released. Passage of protons through the Fo part causes a ring of approximately 10 subunits to rotate. This rotation in turn drives the rotation of the gamma subunits, which forms part of one of the stalks. The gamma subunit moves between the three beta subunits which are held in place by the second stalk which can be regarded as a stator. The polypeptide called OSCP connects the stator stalk to the assembly of alpha and beta subunits. It is this step that is coupled to proton translocation as energy is required to break the strong bond between ATP and the protein.