Actin is a protein involved in the conversion of chemical energy into mechanical work. ATP is an essential component of the molecule. Actin is a key component of muscle myofibrils which combines with the heavy meromyosin (HMM) portion of the myosin filament to form the highly viscous actomyosin. Actin is characterized by its super-precipitation with myosin, its activation of myosin ATPase (EC 3.6.1.3) at low ionic strength and its depolymerization