Actin is one of the most highly-conserved proteins, differing by no more than 20% in species as diverse as algae and humans .Actin or ACTA is aprotein localized in the I band of the myofibrils in the muscle, Acting together with myosin.Actin takes part in the contraction and relaxation of muscle. Actin exists as a monomer in low salt concentrations, but filaments form rapidly as salt concentration rises, with the consequent hydrolysis of ATP.Each actin protomer binds one molecule of ATP and has one high affinity site for either calcium or magnesium ions, as well as several low affinity sites. It occurs in globular (G-actin) and fibrous (F-actin) forms. Actin is found in all eukaryotic cells (except for nematode sperm). Its other activitiessuch as cell motility, cell division and cytokinesis, vesicle and organelle movement, cell signaling, and the establishment and maintenance of cell junctions and cell shape.
