Question

Pepsin, a common enzyme found in the stomach, is most active at pH values between 0.5 and 2.5. It works slowly between pH values of 2.6 and 3.4. Beyond a pH of about 3.5, it becomes completely inactive. Why does this happen?

Answer 1

As pepsin moves into pH range that is no longer highly acidic it works slowly until it becomes inactive because the less acidic the medium is, is the more the pepsin bonds, that is the bonds between the tertiary protein (pepsin is an enzyme), are broken and this cause a shift in the shape of the active site which means it would not be able to accept the substrate for reaction to take place. 

Answer 2

The correct answer is B) The protein chain in the enzyme is denatured, inactivating it as the pH increases past 3.5.