Fig. 4.

Representative scatter plots of 3-day assay variability and Z′ factor determinations. To assess the assay signal windows and variabilities, we performed, for each enzyme, two full 96-well plates of maximum-signal controls (1% DMSO) and two full plates of minimum-signal controls (100 μM cantharidin and 1% DMSO) on 3 consecutive days. Representative assay data for 1-day run were analyzed with Origin^® and are presented as a scatter plot of fluorescence intensity versus well number (two 96-well plates numbered consecutively from 1 to 192 for each set of controls); closed circles are maximum-signal controls and closed squares are minimum-signal controls. The lines going through and bracketing the maximum signal controls indicate the mean (solid line) and ±3 SD (dashed lines) of the maximum control fluorescence intensity. Similarly, the lines going through and bracketing the minimum-signal controls indicate the mean (solid line) and±3 SD (dashed lines) of the maximum control fluorescence intensity, although these are, to a great extent, obscured by the symbols in the plot. (A) Representative PP5C assay data for 1-day run: Z′=0.93. (B) Representative PP1α assay data for 1-day run: Z′=0.90.