Final answer:
The enzyme involved in both somatic hypermutation and isotype switching is activation-induced cytidine deaminase (AID).
Step-by-step explanation:
The enzyme involved in both somatic hypermutation and isotype switching is activation-induced cytidine deaminase (AID).
Somatic hypermutation is the process by which point mutations are introduced into the variable region of immunoglobulin genes, leading to the generation of antibodies with higher affinity for antigens. AID is responsible for this process by deaminating cytosine residues in the variable region of immunoglobulin genes, which then undergo DNA repair pathways resulting in nucleotide substitutions.
Isotype switching, on the other hand, allows B cells to change the class of antibodies they produce from IgM to other classes such as IgG, IgA, or IgE. AID also plays a critical role in isotype switching by inducing DNA double-strand breaks at switch regions in the immunoglobulin gene locus, which then undergoes recombination to switch the constant region.