papain

Papain is a cysteine protease enzyme derived from the latex of the papaya plant (Carica papaya). It belongs to the papain family of proteases and is widely used in industry and research for its ability to hydrolyze peptide bonds in proteins.

Papain is produced as an inactive precursor and is processed to a mature enzyme of about 23 kilodaltons. Its catalytic center uses a cysteine residue (Cys25) and a histidine residue (His159), with an asparagine (Asn175) that helps stabilize the transition state. The enzyme cleaves peptide bonds through nucleophilic attack by the active-site cysteine, with the histidine acting as a base-acid catalyst. It functions best around neutral pH and remains active over a relatively broad pH range, though it is inactivated by heat and certain chemical inhibitors.

Natural sources and production: papain is isolated from the latex of unripe papaya fruit and other parts of the plant. It can be purified from crude latex or produced recombinantly. In addition to its natural form, papain is available in various preparations for industrial and research use.

Applications: in the food industry, papain is used as a meat tenderizer to hydrolyze muscle proteins, improving texture. It is employed in juice and wine clarification and in various protein-processing steps. In medicine and cosmetics, papain has been used in enzymatic debridement and as a digestive aid in some formulations, though medical use requires regulatory oversight and careful handling due to potential irritation or allergic reactions.

Safety and regulation: papain can provoke allergic reactions in individuals with latex or fruit allergies and may cause skin or eye irritation on contact. It should be used according to applicable regulatory guidelines, with appropriate handling and protective measures.