An investigation is carried out on the activity of the protease pepsin, which has an optimum pH of 2.0. Increasing the pH of the pepsin solution from 2.0 to 3.5 causes the rate of protein hydrolysis to fall by 90%. When the pH of the solution is returned to 2.0, the rate of reaction returns to its original maximum value.
Which of the following statements provides the correct biochemical explanation for these observations?
Increasing the pH to 3.5 breaks covalent disulfide bonds within the tertiary structure, which are then re-formed when the hydrogen ion concentration increases at pH 2.0.
Increasing the pH to 3.5 alters the charge of R-groups, disrupting hydrogen and ionic bonds that maintain the active site, which re-form when the pH is restored to 2.0.
The pH change causes irreversible denaturation of the pepsin molecules, but returning the pH to 2.0 provides the activation energy needed to refold the polypeptide chain.
The change in pH hydrolyses the peptide bonds in the primary structure of the enzyme, which spontaneously re-assemble via condensation reactions at pH 2.0.
