The action of papain on leucine methyl ester produces an insoluble polyleucine peptide. Papain breaks down the intercellular matrix of cartilage. Papain is activated by cysteine, sulfide, and sulfite. Activity is enhanced when heavy metal chelating agents such as EDTA are also present. N-bromosuccinimide enhances enzyme activity.
Papain is inhibited by sulfhydryl binding reagents, heavy metals and carbonyl reagents.
Papain may be inactivated by H2O2 generated by gamma-irradiation of H2O as a result of oxidation of the active SH group to sulfenic acid. Stabilizing agents are EDTA, cysteine and dimercaptoethanol. Mercuripapain is recrystallized in the presence of mercury ions. The enzyme activates upon removal of mercury ions to 10 - 20 units per mg of protein. There is also considerable interest in the use of papain for tissue dissociation.