Myosins are a large family of motor proteins found in eukaryotic tissues. They are responsible for actin-based motility. Multiple myosin II molecules generate force in skeletal muscle through a power stroke mechanism fuelled by the energy released from ATP hydrolysis. The power stroke occurs at the release of the products of ATP hydrolysis - ADP and phosphate - when myosin is tightly bound to actin.
Myosin is a protein having a molecular weight of ~ 470,000 daltons. There are about 300 molecules of myosin per thick filament. Each myosin contains two heads that are the site of the myosin ATPase, an enzyme that hydrolyzes ATP required for actin and myosin cross bridge formation. These heads interact with a binding site on actin.