Final answer:
Trypsinogen is converted into active trypsin by the enzyme enterokinase, which is secreted by the intestinal mucosal cells in the small intestine.
Step-by-step explanation:
An enzyme called enterokinase, which is secreted by the intestinal mucosal cells, is responsible for converting trypsinogen into its active form, trypsin, in the small intestine. Trypsin then further activates more trypsinogen as well as other enzymes necessary for protein digestion, like chymotrypsinogen to chymotrypsin. This process is essential to ensure that protein digestion occurs safely without damaging the pancreas or the small intestine, which secrete these enzymes in their inactive zymogen forms.
For example, trypsinogen is converted to trypsin by the removal of a hexapeptide from the N-terminal end.