Which enzyme activates trypsinogen to trypsin in the small intestine?

• A. Trypsin
• B. Chymotrypsin
• C. Enterokinase
• D. Pepsin

Answer: (C)

Enterokinase is the enzyme that activates trypsinogen to trypsin in the small intestine. Pancreatic secretions deliver trypsinogen, an inactive zymogen, into the duodenum. The brush-border enzyme enterokinase (also called enteropeptidase) cleaves a specific portion from trypsinogen, producing active trypsin. Once active, trypsin can then activate other pancreatic zymogens, amplifying digestion. Pepsin operates in the stomach, not the small intestine, and while chymotrypsin is another enzyme that acts downstream, it is activated by trypsin rather than initiating the activation of trypsinogen.