Description
Proteolytic enzymes are widely used in cell isolation. With some tissues papain has proved less damaging and more effective than other proteases. Papain is a sulfhydryl protease from Carica papaya latex. Native crystalline papain is quite unreactive until acted upon by mild reducing agents such as cysteine or cyanide. It may exist as a zymogen (Brocklehurst and Kierstan, 1973). For a general review, see Liener (1974). 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 a single peptide chain of 211 residues folded into two parts that form a cleft. A three-dimensional structure has been indicated. The molecule has one free SH group which is functional. There are seven subsites, each is capable of accommodating a single amino acid residue of a peptide substrate