Summary of pH-independent Pi dissociation constants for AP active site nucleophile mutants.

—, not applicable.aDissociation constant for binding to deprotonated Ser102 as defined in Figure 4C from the measured pH-dependent Pi affinity in Figure 4A for R166S AP and Figure S9C for WT AP. Note that binding of results in a proton transfer to the enzyme as illustrated in Equation 1; represents the observed overall binding.bLower limit of the dissociation constant for binding to deprotonated Ser102 AP determined as described in Text S6 and Figure S9.cUpper limit for the dissociation constant for binding to protonated Ser102 AP as described in the main text and Figure 5.dDissociation constant for binding to S102G AP estimated from the measured affinity of S102G/R166S AP and the expected contribution of Arg166 of 240-fold to the affinity (cf., for WT and R166S AP). The dissociation constant for binding to S102G/R166S AP was determined from the pH-dependent binding data in Figure 4A and is defined in the model in Figure 4D.eDissociation constant for binding to S102G AP estimated based on an expected binding contribution from Arg166 of ∼10-fold (Text S12), and the dissociation constant for binding to S102G/R166S AP determined from the pH-dependent binding in Figure 4A; is defined in the model in Figure 4D.