Fig. 1.

Chemo-mechanical cycle of the interaction of myosin heads with actin. The pre-stroke S1 with bound ADP (D) and inorganic phosphate (Pi) binds to actin (yellow); while bound to actin, the lever arm swings to the left about a fulcrum point (black dot on white star), moving the actin filament to the right (bold blue arrow) with respect to the myosin thick filament; ADP release allows a further small stroke to the post-stroke position and frees the active site for binding of ATP (T); ATP binding weakens the interaction of the S1 to actin; ATP hydrolysis locks the head into the pre-stroke state, which when functionally accessible for interaction with actin is in a disordered relaxed (DRX) state