Active site–located EPP mutations. The catalytically essential H263 (which is not an identified EPP mutation) is shown as a CPK space-filling model with carbon atoms colored violet as a landmark for the central portion of the active-site pocket. EPP active-site mutant residues described in the present study are at positions P334 (carbons in green), Y191 (carbons in light gray), and S264 (carbons in yellow). All structure figures were generated with PyMOL.⁴⁶