Which enzyme is active in the stomach to digest protein?

• A. Lipase
• B. Amylase
• C. Lactase
• D. Pepsin

Answer: (D)

Protein digestion in the stomach is carried out by pepsin. Pepsin is secreted as pepsinogen by the stomach’s chief cells and is activated by the acidic environment produced by hydrochloric acid. In this low pH, pepsin cleaves peptide bonds within proteins, starting their digestion into smaller polypeptides right in the stomach. The other enzymes mentioned target different macromolecules and aren’t functioning to digest proteins in the stomach: lipase works on fats (with gastric lipase present but not the primary enzyme for protein digestion), amylase digests carbohydrates and is active in the mouth and small intestine, and lactase breaks down lactose in the small intestine. So pepsin is the enzyme responsible for protein digestion in the stomach.