Isolation and characterization of E-64, a new thiol protease inhibitor.

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 C15N5H27O5 (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.