Optimal pH for Gastric Protease Activity

Steps:

• Identify gastric protease as pepsin, which functions in the stomach's acidic environment.
• Recall pepsin's optimal activity at pH 1.5–2.5, with reduced activity at higher pH due to denaturation.
• Evaluate graphs for a peak in the acidic range (pH 1–3) and decline toward neutral pH.
• Select the graph matching this profile, confirming it as A.

Why A is correct:

• It shows peak enzyme activity at low pH (around 2), aligning with pepsin's adaptation to stomach acidity per enzyme-substrate complex stability.

Why the others are wrong:

• B peaks at neutral pH, suiting pancreatic enzymes, not gastric ones.
• C shows broad activity across pH, ignoring pepsin's acid specificity.
• D peaks at alkaline pH, typical for intestinal proteases like trypsin.

Final answer: A