So we have a high concentration on the lumen side, a low concentration of calcium on the cytoplasmic side. So this is our ptype Atpas. In this case it's the calcium Atpas. And notice it exists in a specific type of conformation. And the conformation basically allows the movement of these calcium ions into this region of that transmembrane protein. Once the calcium moves in, this uses ATP, it hydrolyzes ATP that creates a conformational change.