At which pH does the enzyme pepsin become most active?

• A. Around pH 7
• B. Around pH 9
• C. Around pH 12
• D. Around pH 2

Answer: (D)

Verified step by step guidance

1. Understand the context: Pepsin is a digestive enzyme that functions in the stomach, where the environment is highly acidic due to the presence of gastric acid (primarily hydrochloric acid). This provides a clue that pepsin is active at low pH values.
2. Recall the concept of enzyme activity and pH: Enzymes have an optimal pH at which they function most efficiently. For pepsin, this optimal pH is in the acidic range because it is adapted to the stomach's environment.
3. Analyze the options: The given pH values are 2, 7, 9, and 12. Among these, pH 2 is the most acidic, while pH 7 is neutral, and pH 9 and 12 are increasingly basic. Pepsin, being an enzyme in the stomach, is unlikely to function well at neutral or basic pH levels.
4. Correlate the enzyme's function with its environment: Since pepsin operates in the stomach, where the pH is maintained around 1.5 to 3 due to gastric acid, its activity is highest in this acidic range. This aligns with the given answer of pH 2.
5. Conclude: Based on the physiological environment of the stomach and the properties of pepsin, the enzyme is most active around pH 2, which is consistent with its role in protein digestion in acidic conditions.