Fig. 1

Schematic diagram of the kinetic cycle of SERCA pump. During the transportation of Ca²⁺ ions, ATP binding is coupled with the change of conformational states of SERCA from E₁ to E₂. These two states have different affinity to Ca²⁺ ions, with E₁ being highly affinitive and E₂ being low. Each time, there are two Ca²⁺ ions and an ATP molecule binding to E₁ state (E₁Ca₂ATP), then after the hydrolysis of ATP the state of SERCA is changed to E₂ (E₂Ca₂P) with the release of ADP. The release of Ca²⁺ ions into the SR lumen requires the exchange of luminal protons on E₂ state (E₂H₂P). The final step is dephosphorylation and dehydrogenation to return the enzyme to the ground state, E₁, which then is able to initiate a new transport cycle. Figure reproduced based on Periasamy et al. 2007 [51]