In duodenal contents of these patients, all pancreatic proteolytic enzymes are present in their inactive form (zymogens). Enteropeptidase is responsible for the activation of trypsinogen to trypsin. The data presented here demonstrate that enteropeptidase plays the key role for the cascade of activation processes which lead to active proteolytic enzymes in the human intestine.

Pancreatic acinar cells synthesize digestive enzymes as inactive zymogens that are stored in zymogen granules and secreted into the duodenum. Once in duodenum, enteropeptidase activates trypsinogen by removing 7–10 amino acid from N-terminal region known as trypsinogen activation peptide (TAP). Removal of TAP induces conformational change resulting in active trypsin. Trypsin then activates other digestive zymogens such as chymotrypsinogen and procarboxypeptidase in the intestinal lumen. This spatial separation and zymogen storage in granules are important protective mechanisms that limit autodigestion of the pancreas.

Enterokinase is a protease of the intestinal brush border that specifically cleaves the acidic propeptide from trypsinogen to yield active trypsin. This cleavage initiates a cascade of proteolytic reactions leading to the activation of many pancreatic zymogens. Enterokinase activates bovine trypsinogen by cleaving after the sequence VDDDDK, releasing an amino-terminal activation peptide. This reciprocal specificity protects trypsinogen against autoactivation by trypsin and promotes activation by enterokinase in the gut.

The zymogens of trypsin and chymotrypsin are secreted into the duodenum in pancreatic juice and are activated in the intestinal lumen. Previous studies have indicated that trypsinogen is activated by enterokinase and that activated trypsin then activates chymotrypsinogen.

Trypsinogen is an inactive precursor of the enzyme trypsin. It is produced by the pancreas and released into the small intestine, where it is **activated to trypsin by an enzyme in the intestinal mucosa called enterokinase (enteropeptidase)**. Trypsin then **activates other pancreatic digestive enzyme precursors**. This system of secreting inactive precursors and activating them only in the intestine is important for **protecting the pancreas from self-digestion**.

Enteropeptidase (enterokinase) is localized to the brush border membrane of duodenal enterocytes and is responsible for the initial step in the activation of pancreatic proteolytic enzymes. It converts trypsinogen to trypsin in the duodenal lumen, thereby initiating a cascade in which trypsin activates the remaining pancreatic zymogens, including chymotrypsinogen, proelastase, and procarboxypeptidases. The strict control of this activation step is essential to prevent intrapancreatic activation of trypsinogen and subsequent pancreatitis.

Under normal circumstances, pancreatic proteolytic enzymes are synthesized and secreted as inactive zymogens. They become activated only after reaching the duodenum, where enterokinase converts trypsinogen to trypsin. This spatial separation of enzyme activation from the pancreas helps prevent autodigestion of pancreatic tissue.

Trypsin and chymotrypsin, like most proteolytic enzymes, are synthesized as inactive zymogen precursors (trypsinogen and chymotrypsinogen) to prevent unwanted destruction of cellular proteins, and to regulate when and where enzyme activity occurs. The inactive zymogens are secreted into the duodenum, where they travel the small and large intestines prior to excretion. Zymogens are converted to the mature, active enzyme by proteolysis to split off a pro-peptide, either in a subcellular compartment or in an extracellular space where they are required for digestion.

Pancreatic enzymes are digestive proteins produced by the pancreas that break down carbohydrates, proteins, and fats. They are **initially secreted in inactive forms called zymogens to prevent self-digestion of the pancreas and surrounding tissues**. In the small intestine, enzymes like **enterokinase convert trypsinogen into trypsin, which then activates other pancreatic enzymes**, ensuring digestion occurs only in the intestine. Delaying enzyme activation until reaching the small intestine **protects the pancreas from autodigestion and inflammation**.

It is produced in the pancreas as an inactive precursor, trypsinogen, and is then secreted into the small intestine. Here, it is activated to its functional form, trypsin, by the enzyme enteropeptidase. Enteropeptidase, an enzyme located on the brush border of the duodenum, recognizes and cleaves a specific peptide bond in trypsinogen, converting it into active trypsin. Once activated, trypsin can also catalyze the conversion of more trypsinogen to trypsin, a process known as autocatalysis.

Major physiology texts (e.g., Guyton & Hall, Ganong, Boron & Boulpaep) describe that pancreatic acinar cells synthesize proteolytic enzymes such as trypsin and chymotrypsin as inactive zymogens (trypsinogen, chymotrypsinogen). These are stored in zymogen granules and secreted into the duodenum, where enterokinase on the duodenal brush border cleaves trypsinogen to trypsin, which then activates chymotrypsinogen and other zymogens. The zymogen form and intestinal-site activation are explicitly presented as mechanisms to prevent autodigestion of the pancreas.