The N-acetylglucosamine phosphatidylinositol (GlcNAc-PI) de-. N-acetylase catalyzes the removal of the N-acetyl group from GlcNAc-PI in the second step of GPI biosynthesis. The GlcNAc-PI de-. N-acetylase is a 252-residue integral membrane protein containing a single N-terminal membrane spanning domain, with the majority of the protein on the cytoplasmic face of the ER. Site-directed mutagenesis studies have lead to the proposal of a zinc-dependent mechanism of action analogous to zinc peptidases. The activity of the GlcNAc-PI de-. N-acetylase can be measured both in vivo and in vitro, and active recombinant protein has been obtained. The enzyme is a potential drug target for the treatment of African sleeping sickness, and differences in substrate recognition and channeling between mammalian and trypanosomal enzymes have been exploited to produce species-specific inhibitors.