The stoichiometry, assembly, and function of the NKA-regulatory complex.A–E, alternative models of NKA-regulatory complex stoichiometry. The present data are consistent with Stoichiometry Model D. F, a model of conformational coupling in a dimer of α subunits. An energetically favorable catalytic step of one protomer (green arrow) assists a rate limiting step (red arrow) of the other partner, enhancing overall turnover. NKA, Na/K-ATPase.