Virtual compound experiment. A, the relationship between free p38 and a 'virtual p38 inhibitor' is shown schematically. B, the dose-response of ATF2 phosphorylation is simulated for the virtual p38 inhibitor using multiple kinetic mechanisms. C, phosphorylation of MK2 (top) and ATF2 (bottom) by p38 was experimentally measured for varying concentrations of the 'virtual p38 inhibitor' under presence of 10 nM MK2 and 100 nM ATF2. The IC50 of the 'virtual p38 inhibitor' for phospho-MK2 and phospho-ATF2 are listed in Table 3. Data is shown ± standard deviation (n = 4).