myosin my·o·sin (mī'ə-sĭn)
The commonest protein in muscle cells, a globulin responsible for the elastic and contractile properties of muscle and combining with actin to form actomyosin.
A protein found in muscle tissue as a thick filament made up of an aggregate of similar proteins. Myosin and the protein actin form the contractile units (sarcomeres) of skeletal muscle. In the sarcomere, actin and myosin filaments slide past each other to cause the shortening of a muscle fiber.