<P> 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 phosphate from the myosin molecule after the ATP hydrolysis while myosin is tightly bound to actin . The effect of this release is a conformational change in the molecule that pulls against the actin . The release of the ADP molecule leads to the so - called rigor state of myosin . The binding of a new ATP molecule will release myosin from actin . ATP hydrolysis within the myosin will cause it to bind to actin again to repeat the cycle . The combined effect of the myriad power strokes causes the muscle to contract . </P> <P> The wide variety of myosin genes found throughout the eukaryotic phyla were named according to different schemes as they were discovered . The nomenclature can therefore be somewhat confusing when attempting to compare the functions of myosin proteins within and between organisms . </P> <P> Skeletal muscle myosin, the most conspicuous of the myosin superfamily due to its abundance in muscle fibers, was the first to be discovered . This protein makes up part of the sarcomere and forms macromolecular filaments composed of multiple myosin subunits . Similar filament - forming myosin proteins were found in cardiac muscle, smooth muscle, and nonmuscle cells . However, beginning in the 1970s, researchers began to discover new myosin genes in simple eukaryotes encoding proteins that acted as monomers and were therefore entitled Class I myosins . These new myosins were collectively termed "unconventional myosins" and have been found in many tissues other than muscle . These new superfamily members have been grouped according to phylogenetic relationships derived from a comparison of the amino acid sequences of their head domains, with each class being assigned a Roman numeral (see phylogenetic tree). The unconventional myosins also have divergent tail domains, suggesting unique functions . The now diverse array of myosins likely evolved from an ancestral precursor (see picture). </P> <P> Analysis of the amino acid sequences of different myosins shows great variability among the tail domains, but strong conservation of head domain sequences . Presumably this is so the myosins may interact, via their tails, with a large number of different cargoes, while the goal in each case--to move along actin filaments--remains the same and therefore requires the same machinery in the motor . For example, the human genome contains over 40 different myosin genes . </P>

Where is myosin found in the skeletal muscle cells