Ward and colleagues (1997) reported that a
protease is required for excystation of Giardia. The
authors observed that specifi c cysteine protease inhibitors block excystation. The protease was localised to vesicles that release their contents just prior
to excystation, and this protease is a member of the
earliest known branch of the cathepsin B family, a
primitive enzyme. In addition, Slavin and collaborators (2002) demonstrated that dephosphorylation
of cyst wall proteins by a secreted lysosomal acid
phosphatase is essential for excystation of Giardia
lamblia.