Isolation and Characterization of E–64, a New Thiol Protease Inhibitor

Abstract
A new thiol protease inhibitor, named E–64, was isolated from the extract of a solid culture of Aspergillus japonicus TPR–64 freshly isolated from soil. E–64 was obtained as white needles and the empirical formula was estimated to be C15N5–H27O5 (M. W. 357). This was almost neutral in its electrophoretic behavior and proved to be a specific and strong inhibitor toward thiol protease such as papain and cathepsin B. They combine equimolecularly and irreversibly.