Papain

Papain is a broad-spectrum cysteine protease derived from the latex of the Carica papaya (papaya) fruit. It consists of a single peptide chain with three disulfide bridges. It exhibits strong proteolytic activity across a wide pH range and is highly stable in various biochemical and industrial conditions. Due to its specificity (preference towards arginine, lysine, and phenylalanine), effectiveness, safety profile, and natural origin, papain is widely used in both research and commercial applications.

Papain catalyzes the hydrolysis of peptide bonds, with a preference for cleaving at sites containing large hydrophobic amino acids such as phenylalanine, tryptophan, and tyrosine. It acts via a catalytic triad mechanism involving a cysteine thiol (Cys-25) and a histidine residue (His-159), enabling nucleophilic attack on peptide bonds.

• Optimal pH: 6.0–7.0 (active in pH 3–10 range)
• Temperature Stability: Active up to ~65°C
• Inhibitors: E-64, iodoacetamide (typical for cysteine proteases)

Papain's enzymatic activity proceeds through:

1. Nucleophilic attack by its catalytic cysteine on the carbonyl carbon of a peptide bond.
2. Formation of a covalent acyl-enzyme intermediate.
3. Hydrolysis of the intermediate to release cleaved peptide fragments.

This thiol-based catalysis is comparable to that of other cysteine proteases like cathepsins.

• Protein digestion and analysis in proteomics and enzymology
• Tissue dissociation for cell culture and primary cell isolation (e.g., neural tissue)
• Morphological isolation of intact cortical neurons from postnatal rats
• Enzyme kinetics and inhibitor studies in drug discovery
• Production of Fab fragments of antibodies
• Model protease for studying structure-function relationships in cysteine proteases
• Enzymatic synthesis of amino acids, peptides, and other molecules

• Available as white to slightly yellow lyophilized powder
• Store at 2–8°C (dry form); keep frozen at –20°C for long-term enzyme stability