Which of the following is not an inactive enzyme released by the pancreas?

The choice of pepsinogen as the answer is based on its origin and function in the digestive system. Pepsinogen is not an enzyme released by the pancreas; rather, it is secreted by the gastric mucosa in the stomach. When pepsinogen encounters the acid in the stomach, it is activated to pepsin, an active enzyme that begins protein digestion.

In contrast, trypsinogen, chymotrypsinogen, and proelastase are all inactive precursors of enzymes produced by the pancreas. These proenzymes are secreted into the small intestine, where they are activated into their respective active forms. The pancreas releases these inactive forms to prevent the enzymes from digesting pancreatic tissue before they reach the small intestine. Thus, distinguishing pepsinogen’s source from the others underscores why it is not categorized as an inactive enzyme from the pancreas.