Enterokinase is a member of the trypsin family of serine proteases. The precursor protein is cleaved into two chains which then forms a heterodimer linked by a disulfide bond. The heavy chain anchors enterokinase in the intestinal brush border membrane and the light chain is the catalytic subunit, which initiates conversion activation of a subset of pancreatic proteolytic proenzymes. Enterokinase is the physiological activator of trypsinogen and has a specificity for the sequence (Asp)4-Lys-Ile. The mature trypsin in turn activates other proenzymes including chymotrypsinogen, procarboxypeptidases, and proelastases. In addition, Enterokinase is a tool protease widely utilized in the cleavage of recombinant fusion proteins.