In experiments testing different pH levels (7.0, 2.0, 9.0), at which pH was amylase activity highest?

• A. pH 7.0
• B. pH 2.0
• C. pH 9.0
• D. All pH values showed equal activity

Answer: (A)

Enzyme activity depends on pH because pH changes alter the ionization of amino acid residues at the active site and the overall shape of the enzyme. Each enzyme has an optimal pH where its active site is properly charged and shaped to bind the substrate and catalyze the reaction most efficiently.

Amylase is most active around neutral pH, near 7.0. At this pH, the active site residues are in the right ionization state to interact with starch and facilitate hydrolysis quickly.

At a strongly acidic pH like 2.0, the enzyme’s structure and charge distribution are disrupted, often leading to denaturation or markedly reduced activity, so the reaction rate drops. At a strongly basic pH like 9.0, critical residues can be deprotonated, also hindering substrate binding and catalysis, which again lowers activity.

Thus, the highest amylase activity is observed at neutral pH (about 7.0).