Glutathione synthetase belongs to which enzyme class?

• A. Oxidoreductase
• B. Transferase
• C. Hydrolase
• D. Ligase

Answer: (D)

Enzyme classifications are based on the type of chemical reaction they catalyze. Glutathione synthetase drives the formation of a new covalent bond to join substrates into a larger molecule, with ATP providing the energy to power that bond formation. This bond-forming, energy-driven process is the hallmark of ligases. In making glutathione, it links the components to form the tripeptide, a reaction that requires ATP. It isn’t an oxidoreductase (no redox change), nor a transferase (no simple transfer of a functional group between molecules), nor a hydrolase (no bond cleavage with water). Hence, it belongs to the ligase class.