Which statement best explains how pH affects enzyme activity under optimal enzyme conditions?

• A. pH affects enzyme activity only by changing the substrate concentration, not by altering enzyme structure or active-site chemistry.
• B. Changing pH alters the ionization states of amino acid side chains (including those in the active site), which can change substrate binding and catalytic activity, producing an optimal pH with decreased activity at more acidic or basic values.
• C. Lowering pH always increases enzyme activity by increasing molecular collisions between enzyme and substrate.
• D. Enzyme activity is independent of pH because the primary amino acid sequence does not change with pH.

Answer: (B)