ATPase alkali-cation

There are several mammalian members of alkali cation ATPases the Na,K ATPases, the H,K ATPases, the SERCA (sarcoplasmic and endoplasmic reticulum), Ca -transport ATPases, and the PM (plasma membrane) Ca ATPase. The fungal H ATPases also belong to this family. Characteristically, the mammalian enzymes all perform countertransport—exchange of a cellular cation with an extracellular cation. The fungal enzymes transport only H outward. The parietal cell possesses a variety of these small alkali cation ATPases, each subserving a different function, but the pump of clinical interest is the pump responsible for acid secretion, the H,K ATPase. 

Why do you think corand 4.12 ([24]aneN602) is such an effective ATPase mimic given the discussion of the relatively low affinity for guest species such as alkali metal cations and halide anions set out in Chapters 3 and 4 Similarly, why was a hemispherand chosen as the central cation-binding core of enzyme mimic 12.16 as opposed to a spherand ... 

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