Molecule models of the calcium-binding protein calmodulin (CaM). The molecule at left has four calcium ions (red) bound to it, the maximum number a single molecule can bind, and is therefore in its active state. The molecule at right has no calcium ions bound to it and is in the inactive state. Activation changes the shape of the molecule, allowing it to bind to target proteins. CaM is found in all eukaryotic cells, where it regulates and modifies the activities of many calcium-binding enzymes. Cellular processes that CaM affects include muscle contraction, inflammation, immune response and memory.