FIGURE 10.

Proposal of a reaction scheme accounting for Ca²⁺ and H⁺ ion interaction with the binding sites of the SR Ca-ATPase in the E₁ conformation. The transitions between states of the ion pump enclosed by the box represent the reaction sequence under physiological conditions; they are part of the Post-Albers cycle. The labeling as “fast” and “slow” transitions indicates the two classes of reaction steps in which, respectively, diffusion-controlled ion movements and binding/coordination of ions happen or conformational rearrangements of the protein occur which modify the access to binding sites.