What is the function of FAD?

• A. Transfers electrons
• B. Shuttles hydrogen from one molecule to another in enzyme catalyzed reactions
• C. Acts as a structural cofactor
• D. Functions as a pH buffer

Answer: (B)

FAD is a redox-active cofactor that stores and transfers hydrogen during enzyme-catalyzed reactions. It accepts two electrons and two protons to become FADH2, effectively taking up hydrogen atoms from one substrate and then delivering them to another substrate in the catalytic cycle. This ability to shuttle hydrogen (as electrons and protons) between molecules is what lets FAD function as a carrier in many dehydrogenase steps and in parts of the electron transport chain. While it does participate in electron transfer, the core idea is its role in moving hydrogen atoms within the reaction sequence, which is why this description best matches FAD’s function.