Question

Why does the enzyme pepsin (present in the stomach) denature in the intestine?

Answer 1

Pepsin is most active in acidic environments. Accordingly its primary site of synthesis and activity is in the stomach.

Explanation:

Pepsin works best at a pH of 2 . This is why it works very well in the acidic condition of the stomach.

The small intestine releases bicarbonate to buffer the acidic pH of pepsin. The pH is about 8 , which is too high for pepsin.
Thus it denatures in the small intestine.