Figure 13.

Summary of the effects of Ala mutations on the Tyr57 pK_a. Ionized Tyr57 is red, and residues are colored according to the change in the Tyr pK_a value upon mutation of the residue to Ala (ΔpK_a, relative to Asp40Asn). The effects at residue 40 are for mutation from Asn to other neutral residues; mutation to charged residue can have larger effects (Tables 9-10). Crystallographically observed water molecules are colored black. Mutation of Tyr57 eliminates the observed pK_a, as expected (Table 1).