where pK • a is the reference pK a of the residue under consideration. We can use this relationship to calculate ∆G 1 (pH) = ∆∆G 1 + RT log pK • a -pH and ∆G 2 (pH) = ∆∆G 2 + RT log pK • a -pH ; here, pK • a corresponds to the reference pK a of residue B.