Figure 2

Curve fitting of the experimental data of activation of E. coli MetAP by Co²⁺. (A) E. coli MetAP (20 μM) was titrated with increasing concentrations of Co²⁺, and its activity was monitored by fluorescence. This titration curve is adapted from [14]. The linear segment (diagonal dash line) corresponding to data extrapolation intercepts the maximal activity (horizontal dash line). The endpoint for the titration indicates clearly a 1:1 metal/protein molar ratio (vertical dash line). (B) The titration data in (A) was fitted with Eq. (4) (the MIBS model), giving n = 1.0 and K_D = 0.9 μM. (C) The same data was fitted with Eq. (7) (the Hill equation), giving n = 2.3 and K_0.5 = 12.1 μM. In both (B) and (C), residuals of the fitting are shown on top of the plots, and fittings at points of low metal concentrations are shown as inserts. (D) Computed fit values using both models [values for solid lines in (B) and (C)] were plotted against the raw data in a log-scale format (the MIBS model, open circles; the Hill equation model, filled circles). For a perfect fit, the plot would result in a straight line with a slope value of 1 (solid line), which is obtained by plotting the raw data against itself.