The average charge of all ionizable residues at certain pH is a good description of IC of a protein. To make the calculation practical and reliable, only ionizable residues within 15 Å of the binding pocket were included in the search of combinations of protonation states of the protein. In the calculation of the total energetics, intrinsic p𝐾 𝑎 ′𝑠 of the most ionizable residues were assumed to be equal to their p𝐾 𝑎 ′𝑠 in water. For ionizable residue clusters containing the Asp120, Asp158 and Asp162, intrinsic p𝐾 𝑎 calculations were done when the emitter was in the neutral form and applied to the following average charge calculations. The reference p𝐾 𝑎 ′𝑠 values for the aspartate residue and various states of the emitter in water, both in the ground and excited states, essential for PDLD/S-LRA calculations within the enzyme-emitter complex, were derived from DFT calculations as outlined in second 2.3.