FIGURE 3.

Analysis of CheY and PhoB_N time traces by fitting to a single exponential decay. Autophosphorylation time traces for reaction of 5 μm CheY (A) or 5 μm PhoB_N (B) with 60 mm PAM are shown in gray. The best fit to a one-phase exponential decay is shown in dashed black lines. The rate constant from the fit is k_obs for CheY and k_app for PhoB_N. Residuals (the difference between the raw data and the one-exponential decay) are shown at the bottom. C, plot of k_obs versus concentration of PAM for 5 μm CheY fit with linear regression (see Equation 3). The slope of the line gave k_phos/K_S, and the y intercept gave k_dephos. Error bars represent standard deviation from duplicate experiments. D, plot of k_app versus concentration of PAM for 5 μm PhoB_N fit with sigmoidal dose-response curve (see Equation 4). Error bars represent standard deviation from triplicate experiments. Reactions were performed in duplicate for A and C and in triplicate for B and D. Time traces represent the mean of multiple reactions, with standard deviations (not shown for clarity) that were less than 3% of the mean. Most error bars in C and D were smaller than data points.