Question

The enzyme Papain, derived from papaya, is commonly used in food industry as a meat tenderizer. It is a/an:

• A. Serine protease
• B. Metalloprotease
• C. Cysteine protease
• D. Aspartic protease

Hint:

Papain is a classic cysteine protease that uses a thiol group ($-\text{SH}$) on a cysteine residue for catalysis.
It is inhibited by thiol-blocking reagents like iodoacetamide or E-64.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Proteases (peptidases) are enzymes that hydrolyze peptide bonds in proteins.
They are classified into families based on the active-site amino acid residue or cofactor involved in the catalytic mechanism.

Step 2: Detailed Explanation:
Papain is a plant-derived proteolytic enzyme obtained from the latex of the green papaya fruit (Carica papaya).
It belongs to the family of cysteine proteases (also known as thiol proteases).
The catalytic mechanism of papain relies on a nucleophilic cysteine residue (Cys-25) and an adjacent histidine residue (His-159) within the active site, which form a thiolate-imidazolium ion pair.
The thiol group of the cysteine residue attacks the carbonyl carbon of the peptide bond, forming a covalent acyl-enzyme intermediate that is subsequently hydrolyzed to release the cleaved peptide.
Because of its ability to break down tough muscle fibers (collagen and actomyosin), papain is widely used as a meat tenderizer in the food industry.
Other protease classes listed include:
- Serine proteases (using an active-site serine, e.g., trypsin, chymotrypsin).
- Metalloproteases (requiring a metal ion cofactor like zinc, e.g., thermolysin).
- Aspartic proteases (using active-site aspartic acid residues, e.g., pepsin).

Step 3: Final Answer:
Papain is a Cysteine protease, which corresponds to Option (C).