Just as every enzyme has an optimal temperature it also has an optimal pH at which it's most active. The activity decreases when the pH tends to get lower or higher than the optimum. This is mainly because the amino acid side chains act as weak acids and bases performing critical functions in the enzyme active site. Enzymes like pepsin have a ...
The expert explains how the rate of many enzyme catalyzed reactions varies with pH. The types of amino acids must be at the active site of an enzyme if its rate decreases at high pH is given.