Cell membrane Cytosol Exterior Calcium binding Enzyme Calcium sites ions ATP binding site 1.When calcium ions bind to the enzyme,the ATP-binding site is activated. 例：Ca2+的 ATP 过膜运输 2.The terminal phosphate group of the ATP binds to ADP the enzyme,causing a conformational change tha transports Ca'+to the exterior. 3.The calcium ions are released to the exterior.例：Ca2+的 过膜运输