Which of the following is a proteolytic enzyme that fragments IgG in three fragments?

The proteolytic enzyme that fragments immunoglobulin G (IgG) into three distinct fragments is papain. When papain acts on IgG, it cleaves the molecule near the hinge region, resulting in two Fab regions (the antigen-binding fragments) and one Fc region (the fragment that mediates effector functions). This specific fragmentation pattern is crucial for various applications in immunology, such as the development of antibody fragments for therapeutic and diagnostic purposes.

Other enzymes listed do not exhibit this specific cleavage pattern associated with IgG. For example, caspases are involved in apoptosis and do not specifically cleave antibodies. C1q is a component of the complement system that binds to antibodies but is not a proteolytic enzyme itself. Trypsin, while also a protease, does not specifically fragment IgG into the three-fragment structure produced by papain. Thus, the unique mechanism of papain makes it the correct answer for this question regarding the fragmentation of IgG.