MG-132 (Z-Leu-Leu-Leu-al) is a potent proteasome and calpain inhibitor with IC50s of 100 nM and 1.2 μM, respectively. MG-132 effectively blocks the proteolytic activity of the 26S proteasome complex. MG-132, a peptide aldehyde, also is an autophagy activator. MG-132 also induces apoptosis.