FIGURE 2.

Conditional Mg²⁺ affinity for phosphate oxygens upon K⁺ binding. Each square represents in a color scale the affinity of Mg²⁺ on a specific binding site (vertical axis) when a K⁺ is close to another binding site (horizontal axis). Since K⁺ rarely occupies some of the binding sites, statistical errors for those sites are large. An equivalent matrix including all the Mg²⁺ binding sites is reported in Supplemental Information 6.