Fig. 4.

Effect of pH on K_d^app for TDG with DACM-labeled or MIANS-labeled V331C LacY. Time traces from TDG titration experiments were recorded at indicated ambient pH values with excitation and emission wavelengths at 397 and 440 nm for DACM- or 330 and 415 nm for MIANS-labeled LacY, respectively. Data collection and fitting details were as described in Fig. 3A (see also Figs. S3–S5). K_d^app values estimated from titrations at each pH were plotted versus H⁺ concentration and fitted with a hyperbolic equation (see Fig. S5); they are presented as a function of pH. Estimated pK_a values are 10.9 and 10.7 for DACM-labeled (●) and MIANS-labeled (▾) V331C LacY.