Inhibition of the enzymatic activities of the 26S proteasome by the CLE in intact MDA-MB-231 breast cancer cell line. Intact MDA-MB-231 were treated for 24 h with or without the CLE followed by 2 h incubation at 37°C with the fluorogenic substrate for Ch-L or T-L or Cp-L activities respectively. The fluorescent intensity of the free AMCs was determined in a multimode reader with excitation (380 nm) and emission (460 nm). Each activity was expressed as the percentage of the control (defined as 100%). Panel A, B &C represents Ch-L, T-L and Cp-L activities respectively.