Inhibition of the enzymatic activities of the 26S proteasome by the CLE in intact MCF-7 breast cancer cell line and WI-38 normal cell line. Intact MCF-7 or WI-38 cells were treated for 24 h with or without the CLE followed by 2 h incubation at 37°C with the fluorogenic substrate for either 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 D depicts results from WI-38 cells. Panels A &D represents Ch-L activity; panels B &C depicts T-L and Cp-L activities respectively.