CTSZ, also known as cathepsin Z/X, is a relatively new cysteine protease of the papain family. Compared to other members of the papain family, CTSZ has a short proregion and unique insertions. Acting as a carboxypeptidase, CTSZ displays a unique specificity. Recombinant mouse CTSZ, fused to His-tag at C-terminus, was expressed in insect cell and purified by using conventional chromatography techniques.