How Much Do You Know about Papain

Basics
Papain is a proteolytic enzyme. Papain is a low-specificity proteolytic enzyme contained in Cariaapapaya. It is widely found in the roots, stems, leaves and fruits of papaya, and is most abundant in immature milk. The active center of papain contains cysteine, which belongs to thiol protease. It has high enzyme activity, good thermal stability, natural hygiene and safety, etc. It is widely used in food, medicine, feed, daily chemical, leather and textile industries application.
Composition
Papaya immature fruit contains various proteolytic enzymes such as papain, Chymopapain A, Chym opapain B, and Papaya Peptidase B. It is also known that the primary structure of four cysteine proteases has a high degree of homology. Among them, papain is a thiol protease, which hydrolyzes the carboxy terminus of arginine and lysine in proteins and peptides, and preferentially hydrolyzes peptides having amino acids or aromatic L-amino acids having two carboxyl groups at the N-terminus of the peptide bond key.
Structural information
Papain is a proteolytic enzyme with a molecular weight of 23,406 and consists of a single peptide chain containing 212 amino acid residues. At least three amino acid residues are present in the active center of the enzyme, which are Cys25, His159 and Asp158, respectively. When Cys25 is oxidized by an oxidant or bound to a metal ion, the activity of the enzyme is inhibited, and the reducing agent cysteine (or Sulfite) or EDTA restores enzyme activity. The other six cysteine residues form three pairs of disulfide bonds and are not at the active site. Pure papain preparations may contain: (1) papain, molecular weight 21000, accounting for about 10% of soluble protein; (2) papaya chymotrypsin, molecular weight 26000, accounting for about 45% of soluble protein; (3) lysozyme, molecular weight 25000, accounting for about 20% of soluble protein; and different enzymes such as cellulase.
Chemical properties
Papain is a protease that decomposes proteins in acidic, neutral, and alkaline environments. Its appearance is white to pale yellow powder, slightly hygroscopic; papain is soluble in water and glycerin, aqueous solution is colorless or light yellow, sometimes milky white; almost insoluble in organic solvents such as ethanol, chloroform and ether. Papain is a thiol-containing (-SH) endopeptidase with protease and esterase activity. It has a wide range of specificities and has strong hydrolysis ability to animal and plant proteins, peptides, esters and amides. But it can hardly break down peptone.
The most suitable pH value of papain is 6–7 (generally 3 to 9.5), and it also plays a role in neutral or acidic. The isoelectric point (pI) is 8.75; the most suitable temperature for papain is 55–65 °C (Generally 10 to 85 ° C can be), heat resistance, not completely deactivated at 90 ° C; inhibited by oxidants, reducing substances activated.
Catalytic mechanism
The mechanism of papain cleavage peptide bond includes: deprotonation of Cys-25 under the action of His-159, and Asn-158 can help the placement of the imidazole ring of His-159, so that deprotonation can occur; then Cys- 25 nucleophilic attack of the carbonyl carbon on the peptide backbone and covalently linked thereto to form an acyl-enzyme intermediate; then the enzyme acts on a water molecule, deacylation occurs, and the carbonyl terminus of the peptide chain is released.
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Creative Enzymes is a US-based biotech company that has rich expertise in enzyme manufacturing, such as Catalase, Pectinase, Glucose Oxidase, for life science research and production of medicines, food, alcohol, beer, fruit juice, fabric, paper, leather goods, etc.