Fig. 4.

Inhibition of the cell-based cleavage of the 3CL^pro by the Isatis indigotica root extract. Vero cells generating the 3CL^pro–substrate–luciferase fusion protein were treated with the indicated concentration of the I. indigotica root extract. Equal amounts (100 μg) of cell lysates were used to determine the luciferase activity (LUC) using the dual Luciferase Reporter Assay System. The relative inhibition of cell-based cleavage activity was calculated as 1 − (LUC_{with inhibitor})/(LUC_{without inhibitor}).