And notice we have six different diagrams and this basically cycles back and forth. So let's begin with the starting point, this diagram here. So this is known as the e one state of this protein. So this is the calcium Atpas, the lumen side of the sarcoplas reticulum, the cytoplasm side of the sarcoplas reticulum. Now, in the e one stage in the e one state, notice that this structure basically is open to this side of the cytoplasm. And two, not one, but two calcium ions can move into this pocket of the transmembrane domain.