Calomodulin is a calcium (Ca2+)-binding protein. Thus, calmodulin can regulate the control of a large amount of enzymes via Ca2+. Many enzymes are stimulated by the calmodlin-Ca2+ complex, especially protein kinases and phosphatases. Calmodulin contains four EF-hand calcium-binding motifs, and thus binds four calcium ions in the non-apo form. Upon binding of the calcium ions, the protein undergoes a large conformational change. Calmodulin is 148 amino acid residues long. It consists of 8 alpha helices (magenta) and 4 beta strands (blue).