Figure 2.
(a) Fluorescence emission of the substrate (concentration 20 μM) in the presence of 3CLpro (0.2 μM) as a function of time, at varying amounts (0–125 μM) of (a) eugenol and (b) estragole. The initial slope of the curves quantifies the enzymatic protein activity. The arrows indicate the increase in inhibitor concentration. (c) Inhibition curve for eugenol (open squares) and estragole (closed squares). The continuous line is from a non-linear least squares regression fit, and provides the inhibition constant (Ki = 0.81 and 4.1 μM for eugenol and estragole, respectively). The different colors in (a,b) correspond to the different concentrations shown in (c): 0 (black), 1.95 (red), 3.91 (green), 7.81 (blue), 15.63 (cyan), 31.25 (magenta), 62.5 (yellow), and 125 μM (brown).