An IgG monoclonal antibody is treated with the proteolytic enzyme papain under conditions that cleave the molecule at the hinge region. Which fragments result?

• A Two monovalent Fab fragments and one intact Fc fragment ✓
• B One bivalent F(ab')2 fragment and one degraded Fc fragment
• C Two monovalent Fab fragments and two separate heavy-chain segments
• D One intact molecule with exposed hinge sulfhydryl groups only

Explanation

Papain cleaves IgG on the amino-terminal side of the inter-heavy-chain disulfide bonds at the hinge, yielding three fragments: two identical monovalent Fab fragments, each retaining a single antigen-binding site, and one intact Fc fragment carrying complement-binding and Fc receptor sites. Pepsin, by contrast, cleaves on the carboxy-terminal side of the hinge, producing a single bivalent F(ab')2 fragment that can still cross-link antigen, which is why option B describes pepsin digestion rather than papain digestion.

Reference: Ananthanarayan and Paniker's Textbook of Microbiology, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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