Which interactions stabilize enzyme–substrate complexes?

• A. Only hydrogen bonds
• B. Hydrogen bonds, electrical attraction, or covalent bonds
• C. Only covalent bonds
• D. Van der Waals forces exclusively

Answer: (B)

Enzyme–substrate binding is stabilized by a mix of interactions in the active site, not by a single type. Hydrogen bonds create specific, directional contacts between enzyme and substrate, helping align key functional groups for reaction. Electrostatic attractions between oppositely charged groups further stabilize the complex by holding charged portions of the substrate in place. In some enzymes, a transient covalent bond can form between the enzyme and the substrate, creating a more stable linkage or reactive intermediate that aids catalysis. Because ES complexes are typically held together by several kinds of interactions, the broad combination of hydrogen bonds, electrostatic attractions, and sometimes covalent bonds best captures how these complexes are stabilized. The other options are too narrow: relying only on hydrogen bonds misses ionic interactions (and possible covalent steps), relying only on covalent bonds is uncommon for general stabilization, and focusing exclusively on van der Waals forces excludes the more significant stabilizing interactions described here.