Papain is a cysteine protease consisting of a single polypeptide containing three disulfide bridges. Native crystalline papain is unreactive until acted upon by mild reducing agents, e.g., cysteine, sulfide, or sulfite, and therefore likely exists as a zymogen. Papain has a wide specificity with a preference towards arginine, lysine, and phenylalanine. This enzyme degrades protein substrates such as the intercellular matrices of cartilage more extensively than pancreatic proteases and is typically less damaging and more effective than other proteases for tissue dissociation applications (Huettner & Baugham; Lam) and has also been used for the digestion of neural tissue (Fasano et al.).