Ca2+ ATPase is a protein which enables active transport of Ca2+ across the membrane of cells. This active transport allows the cells to maintain a low concentration of Ca2+ ions in the cytostol which is important for proper inter-cellular signalling.
Hydrolysis of ATP is the powerhouse for this process, as it allows the binding of Ca2+ ions with a ratio of one ATP hydrolysed for each Ca2+ ion bound.
Here you can see Ca2+ATPase in a cellular membrane.
(Image via wikimedia)
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