Papain is an enzyme found in the latex (situated between bark and pulp) of the papaya. It is also found in many plants, as well as in pineapple.
Papain is a cysteine protease of the hydrolase family. This enzyme cleaves the peptide bonds between the amino acids present in proteins.
In biology, the cleavage mechanism used by a cysteine protease is called « catalytic triad ». This name is given in reference to the number of amino acids involved (3) in this cleavage, one of which is a cysteine (sulphur amino acid).