Papain is a proteolytic enzyme that is found in the leaves of papaya trees as well as the fruit itself. The latex of the papaya fruit houses papain as well as chymopapain, another proteolytic enzyme. According to DietandHealth.net, papain has a soothing effect on the stomach and helps in protein digestion. The enzyme is mainly used as a meat tenderizer. By wrapping meat with the leaves of the papaya fruit, the enzymes help break down the tough tissues that connect the muscles. Other popular uses for papain include clotting milk, treating jellyfish and insect stings and the acceleration of wound healing.