Immunoglobulin G (IgG) cleavage: A specific protease (such as papain) splits an IgG molecule into which defined fragments?

Introduction / Context: IgG structure determines how antibodies bind antigen and recruit effector functions. Proteolytic cleavage experiments (papain versus pepsin) are classic tools to map domains and understand function.

Given Data / Assumptions:

• Protease referenced is the classic one used for IgG domain mapping.
• We consider intact IgG with two antigen-binding arms and one constant Fc region.

Concept / Approach: Papain cleaves IgG above the hinge, yielding two monovalent Fab fragments (each with one antigen-binding site) and one Fc fragment (crystallizable fragment mediating effector functions like complement and Fc receptor binding). In contrast, pepsin cuts below the hinge, producing F(ab')2.

Step-by-Step Solution: Recall papain action → cleavage above hinge. Products → Fab + Fab + Fc. Choose the option explicitly naming these three fragments. Confirm that other options describe different outcomes (e.g., pepsin makes F(ab')2).

Verification / Alternative check: Fab retains antigen-binding without effector function; Fc retains constant-region functions without antigen binding.

Why Other Options Are Wrong: Heavy-light dimers not standard nomenclature; random oligopeptides imply nonspecific digestion; F(ab')2 is pepsin product, not papain.

Common Pitfalls: Confusing papain with pepsin; mixing up Fab (monovalent) versus F(ab')2 (bivalent).

Final Answer: Two Fab fragments and one Fc fragment.