enzyme present in the milky juice of the papaya that catalyzes the breakdown of proteins (protein) by hydrolysis (addition of a water molecule). Papain is used in biochemical research involving the analysis of proteins, in preparations of various remedies for indigestion, in tenderizing meat, and in enzyme-action cleansing agents for soft contact lenses. A related enzyme from the same source is chymopapain, which has different characteristics of mobility and solubility. It is used to shrink or dissolve ruptured disks in certain kinds of lumbar spine injuries, and otherwise as a digestant of protein.