Pumping calcium. Ca2+ATPase transports Ca2+ through the membrane by a mechanism that includes (1) Ca2+ binding from the cytoplasm, (2) ATP binding, (3) ATP cleavage with the transfer of a phosphoryl group to Asp 351 on the enzyme, (4) ADP release and eversion of the enzyme to release Ca2+ on the opposite side of the membrane, (5) hydrolysis of the phosphorylaspartate residue, and (6) eversion to prepare for the binding of Ca2+ from the cytoplasm.