At what pH is salivary amylase most active?

• A. pH 7.0
• B. pH 5.0
• C. pH 9.0
• D. pH 2.0

Answer: (A)

Enzymes work best at a pH that keeps their active site correctly shaped and charged for catalysis. Salivary amylase operates most efficiently in near-neutral conditions, which matches the natural pH of saliva in the mouth. At around pH 7.0, the ionization of key amino acids in the enzyme allows substrate binding and chemical work to proceed smoothly, so starch digestion begins as soon as starch is present.

If the environment becomes too acidic, like pH 5.0, or too basic, like pH 9.0, or extremely acidic, such as pH 2.0, the necessary charges and structure of the active site are disrupted. That interference lowers the enzyme’s activity or can denature it, so those pH values are far less favorable for salivary amylase. Thus, pH 7.0 is the peak activity condition for this enzyme.