Pepsinogen is activated by

The proenzyme pepsinogen, on exposure to hydrochloric acid gets converted into the active enzyme pepsin, the proteolytic enzyme of the stomach. Enterokinase converts trypsinogen into trypsin. Castle's intrinsic factor helps in absorption of vitamin B_12. Trypsin converts chymotrypsinogen into chymotrypsin and pro-carboxypeptidase into carboxypeptidase.