Final answer:
ATP's primary role in actin-myosin interaction is to fuel the power stroke that leads to muscle contraction and to enable muscle relaxation by allowing myosin heads to detach from actin filaments.
Step-by-step explanation:
The most basic role of ATP in the process of actin-myosin interaction is to provide the energy necessary for muscle contraction and relaxation. This is achieved through a cycle of processes involving the binding and hydrolysis of ATP by myosin, which ultimately enables the myosin heads to alternately attach to and release from actin filaments. During muscle contraction, ATP is hydrolyzed to ADP and inorganic phosphate (Pi), causing an allosteric change in the myosin head into a high-energy 'cocked' position. This 'cocking' of the myosin head is crucial for the power stroke that pulls the actin filament inward, shortening the muscle. In turn, the binding of new ATP molecules to the myosin heads is required for them to release actin, allowing the muscle to relax and the actin and myosin filaments to slide apart.