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 22.214.171.124) at low ionic strength and its depolymerization, i.e., loss of viscosity, on adding ATP at high ionic strength. Actin is reversibly transformed into a viscous polymerized fibrous form, F-actin, by the addition of neutral salts at a neutral or slightly alkaline pH. The reaction which involves bound nucleotide is:
G-actin-ATP → F-actin-ADP + Pi
Stability/Storage: Stable 1-2 years at 2-8°C. Store at 2-8°C.