Enterokinase, or Enteropeptidase is a type II transmembrane, which is a member of the trypsin family of serine proteases, and plays a key role in mammalian metabolism. It is synthesized as a zymogen (proenteropeptidase) that requires activation by another protease, either trypsin or possibly duodenase. Active enteropeptidase then converts the pancreatic precursor, trypsinogen, to trypsin by cleavage of the specific trypsinogen activation peptide, Asp-Asp-Asp-Asp-Lys- Ile that is highly conserved in vertebrates. The mature trypsin in turn activates other proenzymes including chymotrypsinogen, procarboxypeptidases, and proelastases. Enterokinase consists of two subunits linked by a disulfide bond. The heavy chain achors enterokinase in the intestinal brush border membrane and the light chain is the catalytic subunit, which has the same mechanism of action as trypsin and chymotrypsin. Enterokinase is the physiological activator of trypsinogen and has a specificity for the sequence (Asp)4-Lys-Ile. Because of its high specificity towards the amino acid sequence (Asp)(4)-Lys, enterokinase is a potential tool for the cleavage of fusion proteins, which are gaining more importance in biopharmaceutical production. In addition, Enterokinase is a tool protease widely utilized in the cleavage of recombinant fusion proteins.