Plasma membrane Ca2+ ATPase

The plasma membrane Ca²⁺ ATAase is a transport protein in the plasma membrane of cells that serves to remove calcium (Ca²⁺) from the cell. It is vital for regulating the amount of Ca²⁺ within cells. It is powered by the hydrolysis of adenosine triphosphate (atp), with a stoichiometry of one Ca²⁺ ion removed for each molecule of ATP hydrolysed. It binds tightly to Ca²⁺ ions (has a high affinity, with a K_m of 100 to 200 nM) but does not remove Ca²⁺ at a very fast rate. This is in contrast to the sodium calcium exchanger (NCX), which has a low affinity and a high capacity. Thus the PMCA is effective at binding Ca²⁺ even when its concentrations within the cell are very low, so it is suited for maintaining Ca²⁺ at its normally very low levels. Calcium is an important second messenger, so its levels must be kept low in cells to prevent noise and keep signalling accurate. The NCX is better suited for removing large amounts of Ca²⁺ quickly, as is needed in neurons after an action potential. Thus the activities of the two types of pump complement each other.

Ca²⁺/calmodulin binds and further activates the PMCA, increasing the affinity of the protein's Ca²⁺ binding site 20 to 30 times.

There are at least five types of PMCA. Three types, PMCA1, PMCA2, and PMCA3, occur in the brain in varying distributions.