Which pancreatic protease cleaves peptide bonds in the small intestine?

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Proteolysis in the small intestine relies on pancreatic endopeptidases that cut internal peptide bonds, with trypsin taking the lead role. Trypsin is released as an inactive zymogen and activated in the duodenum by the enzyme enteropeptidase. Once active, it cleaves peptide bonds on the carboxyl side of basic amino acids, specifically lysine and arginine, helping to break proteins into smaller peptides. It also starts a cascade by activating other pancreatic zymogens, like chymotrypsinogen and proelastase, broadening the digestion of proteins.

Carboxypeptidase, by contrast, is an exopeptidase that removes amino acids from the C-terminus of peptides rather than cleaving internal peptide bonds, so it’s less about the broad internal cleavage that characterizes the primary digestion in the small intestine. While other endopeptidases such as chymotrypsin and elastase also cleave internal bonds, trypsin is the best-known pancreatic enzyme responsible for initiating and coordinating this proteolysis in the intestinal lumen.