Figure 6: Probability of deprotonating ionizable residues as a function of pH.

(a) Results for the eight ionizable residues within ${\text{E}}_{\text{4}}{\text{K}}_{\text{4}}$. The green and black vertical lines intersect the abscissa at model compound ${\text{pK}}_{\text{a}}$ values for Glu and Lys, respectively. The horizontal dashed line intersects the ordinate at the value of 0.5. The intersection of this horizontal dashed line with the residue-specific “titration curves” is used to estimate the apparent ${\text{pK}}_{\text{a}}$ value for the residue in question. The curves are colored according to the residues as shown in the legend. (b) Results for the six ionizable residues within NTL9_12–23. The vertical lines shown in blue, green, and cyan intersect the abscissa at pH values that correspond to the model compound ${\text{pK}}_{\text{a}}$ values for Asp, Glu, and Lys, respectively.