Brain cathepsin B cleaves a caspase substrate

We show that an enzyme exists in rat brain capable of cleaving the Caspase-3 specific peptide substrate Ac-DEVD-AMC at low pH. The enzyme shows properties of a cysteine protease and is localized, predominantly, in lysosomes. We have purified this enzyme from rat brain and identified it by MALDI-TOF MS. The enzyme possessing "acidic" DEVDase activity in rat brain appears to be Cathepsin B. It remains obscure, whether Cathepsin B participates in cleavage of Caspase-3 substrates in vivo. We suggest that under certain conditions (e.g. in hypoxia) Cathepsin B participates in cleavage of Caspase-3 substrates in brain cells.