Resolving the Fast Kinetics of Cooperative Binding: Ca2+ Buffering by Calretinin
Figure 3
Fitting of the Ca2+ Uncaging Data with the Model of Two Pairs of Cooperative Sites and One Individual Site
A typical dataset (•) consisting of 14 randomly chosen traces is shown in (A–G). The traces were selected from seven different experimental conditions, two per condition. The table shows the values for the four variables differing in conditions (A–G). Individual data points (•) are fitted with either the new model (red lines) or the MWC model (blue lines), taking into consideration the four variables listed in the table, whereas the values for kon's, koff's, Kd(app), L0, k+(L0), and the nH for CR are identical for all fits within a set. The amount of uncaging is fitted independently for every trace. For the selected examples, it is expressed as percentage of total [DMn]. The gray areas indicate the whole range of uncaging experiments for each experimental condition; the smaller insets in (D–G) show the whole range of traces, whereas the y-axis ranges in the main panels (D–G) were selected to optimally show the 14 selected traces. More individual curves can be seen in Figure S1. Black scale bars in (A–G) insets indicate 50% ΔF/F (y-axis) or 20 ms (x-axis). (H) To assess the goodness of fit by the new model, the averaged relative deviations of the fit from the data are shown as black bars ± the standard error of the mean for the first 20 ms of the fit (left) and for 20–50 ms of the fit (right bar). The largest single deviations in either direction found in all of the sets are indicated by striped bars. The yellow bars indicate the deviation observed in the selected set of traces displayed in (A–G). The scale bar indicates 5% error/deviation from data. In the table for the OGB-5N column, I refers to lot number 34B1–2 and II to lot 15C1–2.