Figure 2:
Generalized Post-Albers cycle for P-type ATPases. E1 and E2 represent conformations with ion-binding sites facing the cytoplasm and extracellular medium, respectively. X and Y are ionic species that are transported consecutively out of and into the cytoplasm with stoichiometries of ν and μ, respectively. (Xν)E1-P, and E2(Yμ) represent occluded states in which the ions are bound within the membrane domain and are unable to exchange with either aqueous phase. E1P and E2P represent states in which a conserved catalytic aspartate residue is phosphorylated. In general, formation of this phospho-enzyme accompanies transport of the X ions out of the cytoplasm in the first half cycle, whereas dephosphorylation and transport of the Y ions into the cytoplasm occurs in the second half cycle.