Thiol protease. Probably involved in interaction with host tissues. Displays a similar activity to that of papain. Has high activity on Z-Phe-Arg-NHMec, but no activity on Z-Arg-NHMec. Strongly inhibited by Antipain, E64 and Leupeptin, and weakly inhibited by iodoacetic acid (IAA) and phenylmethylsulfonyl fluoride (PMSF). Requires the presence of dithiothreitol (DTT) for activity. Optimum pH is 7-9 in a mixed-buffer system. In a Tris buffer high levels of activity were detected at very alkaline pHs. Monomer. Contains cysteine residues involved in intramolecular disulfide bonding. Belongs to the peptidase C1 family. It is not clear whether the mature peptide starts at Ala-107 or at Val-108.