Final answer:
The myosin ATPase mediates the step in the cross bridge cycle where ATP binds to myosin after the power stroke, causing myosin to release actin and hydrolyze ATP into ADP and Pi, which readies myosin for another cycle of interaction.
Step-by-step explanation:
The step of the cross bridge cycle that is mediated by the ATPase activity of myosin occurs after the power stroke. Once a power stroke has occurred, myosin remains bound to the actin filament until a new molecule of ATP binds to the myosin head. Upon ATP binding, myosin releases actin, this is when the ATPase function of myosin comes into play. The bound ATP is then hydrolyzed into ADP and inorganic phosphate (Pi), with the aid of the myosin ATPase enzyme. This hydrolysis releases energy which is used to change the angle of the myosin head into a 'cocked' position, with the myosin head still holding onto ADP and Pi. This 'cocked' myosin is then ready to initiate another cycle of interaction with actin once the ADP and Pi are released.