Papain

Name: Papain
Synonym: Velardon; Vermizym
CAS: 9001-73-4
Botanical Source: Papaya
Major Functions: The mechanism by which it breaks peptide bonds involves deprotonation of Cys-25 by His-159. Asn-158 helps to orient the imidazole ring of His-159 to allow this deprotonation to take place. Cys-25 then performs a nucleophilic attack on the carbonyl carbon of a peptide backbone. This frees the amino terminal of the peptide, and forms a covalent acyl-enzyme intermediate. The enzyme is then deacylated by a water molecule, and releases the carboxy terminal portion of the peptide. In immunology, papain is known to cleave the Fc (crystallisable) portion of immunoglobulins (antibodies) from the Fab (antigen-binding) portion.