Trypsin works best at pH 8 while pepsin works best in acid, which shows that enzymes:

1. Enzymes are polypeptides, so their shape depends on the chemistry around them. 2. Change that chemistry and the active site changes with it. 3. Trypsin, an enzyme in the human small intestine, works most efficiently at pH 8, whereas pepsin in the stomach works best under acidic conditions. 4. So each enzyme has its own optimum, matched to where in the body it works. _Source: OpenStax Biology for AP(R) Courses (CC BY 4.0), Ch 6 'Metabolism', sections 6.1-6.5_