What was the final pH in the tube that showed the highest lipase activity?

• A. 2.0
• B. 7.0
• C. 6.5
• D. 6.21

Answer: (D)

The main idea is that enzyme activity depends on pH because the ionization state of key amino acid residues in the active site must be right for catalysis. In this lipase experiment, the tube that ends at a final pH of 6.21 shows the highest activity because, under the given buffer conditions, lipase operates most efficiently around that pH. At this pH, the catalytic residues are in the proper charge state and the enzyme remains stable enough to hydrolyze triglycerides effectively. If the pH is much lower (like 2.0), the enzyme can become denatured or the active site residues misstate, reducing activity. If the pH is higher (7.0 or 6.5), the enzyme’s catalytic efficiency is not as high in this setup, so less product is formed. The final pH reflects both product formation and the buffering system, and the 6.21 value corresponds to the conditions under which lipase acted most rapidly in this experiment.