The term ionization configuration (IC) is defined as the most favored combination of protonation states of ionizable residues in a protein at certain pH. It is crucial to have a knowledge of the protonation states of the residues around the emitter as it can significantly influence the spectroscopic properties of the emitter. The IC of the studied enzyme-emitter complexes were obtained by p𝐾 𝑎 calculations using the Protein Dipole Langevin Dipole (PDLD) method within the Linear Response Approximation (LRA) framework. The p𝐾 𝑎 of the i th ionizable residue in protein can be calculated by Eqn. (4):