myosin

myosin , one of the two major protein constituents responsible for contraction of muscle. In muscle cells myosin is arranged in long filaments called thick filaments that lie parallel to the microfilaments of actin . In muscle contraction, filaments of actin alternately chemically link and unlink with those of myosin in a creeping or sliding action. The energy for this reaction is supplied by adenosine triphosphate . Myosin and actin also function in the motility of diverse non-muscle cells. In slime molds , for example, although present in much smaller quantities and forming shorter filaments, the interaction of the two proteins is employed to change cell shape and permit some movements.

myosin The predominant protein of the myofibrils of muscle cells. It has an unusual shape for a protein, having a globular head and a rod-like tail.

myosin A contractile protein that interacts with actin to bring about contraction of muscle or cell movement. The type of myosin molecule found in muscle fibres consists of a tail, by which it aggregates with other myosin molecules to form so-called `thick filaments'; and a globular head, which has sites for the attachment of actin and ATP molecules. See sarcomere; sliding filament theory.