It has a molecular weight of 23,000 daltons and an optimum pH range of 6.0 - 7.0. Papain has wide specificity. It will degrade most protein substrates more extensively than the pancreatic proteases. It is also an esterase. 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.