Enzyme Denaturation by Low pH

Steps:

• Low pH increases H+ concentration, altering the charge balance in protein side chains.
• Negatively charged R groups (like carboxylate) protonate, gaining positive charges.
• This charge repulsion disrupts ionic bonds and hydrogen bonds maintaining 3D shape.
• Resulting structural change denatures the enzyme, impairing function.

Why A is correct:

• Protonation of negatively charged R groups (e.g., -COO- to -COOH) introduces repulsive forces, per principles of electrostatic interactions in protein folding.

Why the others are wrong:

• B: Disulfide bonds are covalent and unaffected by pH; they require reducing agents to break.
• C: Low pH decreases, not increases, hydrogen bonding by protonating potential donors/acceptors.
• D: Hydrophilic groups' water affinity changes minimally; denaturation stems from charge disruption, not hydrophilicity.

Final answer: A