FIGURE 1.

Top, properties of hydrated and un-hydrated Ca²⁺ and Mg²⁺. Bottom, Ca²⁺ and Mg²⁺ coordination to an EF protein motif (hypothetical comparison). The binding differences are determined by the chemical properties of the two metals described in Table 1, which explain the ease with which Ca²⁺ accepts binding sites of irregular geometry. Adapted from Ref. 7.