Figure 1.

Dependence of inhibition potency (IC₅₀ values) from substrate concentration for inhibition of cathepsin L by compounds a (left) and b (right). Increasing IC₅₀ values at increasing substrate concentrations prove competitive inhibition; the K_i^(*) value (corresponding to the IC₅₀ value at zero substrate concentration) is obtained as the intercept of the regression line with the y-axis (a: K_i = 1.14 μM and b: K_i^* = 0.030 μM).