Consider the system given in Figure . Relative to As in Example 2, constructing the titration curves computed from the microscopic pK a values reveals the coupling between residues (Figure , bottom). Here, plateaus are evident for both residues over pH ∈ [6, 9], implying the existence of both singly protonated microstates. Moreover, the residue with the higher reference pK • a , perhaps counterintuitively, titrates first.