In the catalytic triad, what role does histidine 57 play in the mechanism of chymotrypsin?

• A. Histidine 57 acts as an acid, donating a hydrogen to serine 195.
• B. Histidine 57 enhances the nucleophilic ability of aspartate 102.
• C. Histidine 57 stabilizes the transition state by forming covalent bonds.
• D. Histidine 57 acts as a base, acquiring a hydrogen from serine 195.

Answer: (D)