Calpain inhibitor II is a cell permeable, peptide aldehyde inhibitor of calpain I (Ki = 120 nM), calpain II (Ki = 230 nM), cathepsin B (Ki = 100 nM), and cathepsin L (Ki = 0.6 nM). It has been used to demonstrate the involvement of ubiquitin-proteasome protein degradation in various biological systems.
