Papain is essentially a cysteine protease enzyme ( EC 3.4.22.2 ) found in papaya . They contain amino acids which are stabilized by three disulfide bridges . In their 3D structure, two distinct structural domains can be seen with a cleft between each. The active site is contained by the cleft which in turn consists of a catalytic triad that likened to chymotrypsin . This catalytic triad is formed of 3 amino acids - cysteine-25, histidine-159, and asparagine-158.

Function :

The mechanism through which papain causes the break down of peptide bonds is referred to as deprotonation of Cys-25 by His-159. Asn-158 supports in the orientation of imidazole ring of His-159 and allows the initiation of deprotonation. Cys-25 then nucleophilic ally attacks the carbonyl carbon of the peptide backbone, freeing the amino terminal of the peptide. This process leads to the formation of covalent acyl-enzyme intermediates. This enzyme is then deacylated by a water molecule, and causes the release of the carboxy terminal portion of the peptide link. Papain is also known to bring about the cleaving of the crystallisable portion of immunoglobulins from the Fab portion.

Uses & Benefits :

•  Papain is majorly employed to cause the break down of tough meat fibers. In super markets, it can be found as powdered meat tenderizer. When mixed to form a paste with water, it is used as a remedy for treating jellyfish , bee , and wasp stings along with mosquito bites and even stingray wounds. It does this by breaking down the protein present in the toxins of the stings.

•  Papain are widely used to dissociate cells in the first stage of cell culture preparations. A 10-minute treatment of small tissues allows papain in the break down of extracellular matrix molecules thereby helping the cells to stay together.

•  Papain find use in the care of chronic wounds to clean up dead tissues as well.

It is included in some toothpastes to be used as a teeth-whitener.