Enterokinase (enteropeptidase, EC 3.4.4.8) occupies a key position in the utilization of dietary proteins. The enzyme initiates intraluminar digestion of proteins by the proteolytic conversion of trypsinogen to trypsin, which in turn activates the other pancreatic zymogens (Kunitz, 1939a,b; Hadorn et al., 1969). The proteolytic attack of enterokinase is directed exclusively toward the Lys6-Ile7 peptide bond of trypsinogen leaving all other lysine and arginine bonds in the molecule unaffected (Maroux et al., 1971). The resultant cleavage produces the simultaneous release of active trypsin and of the 
amino-terminal hexapeptide Val-(Asp)d-Lys (Rovery et al., 1953; Davie and Neurath, 1955). This unique specificity exhibited by enterokinase is of interest as it relates to both the molecular basis of substrate recognition and the control of the digestive process. 

5 U/μL Enterokinase, Bovine in 20 mM Tris-HCl (pH 7.4 @ 25°C), 200 mM NaCl, 2 mM CaCl2 and 50% (v/v) glycerol

Optimal incubation times and enzyme concentrations must be determined empirically for a particular substrate. Typical reaction conditions are as follows:
1. Combine 500 ug of sample with reaction buffer
* Recommended Reaction Buffer: 20 mM Tris-HCl, 50 mM NaCl, 2 mM CaCl2 (pH 8.0)
2. Add 1 U of Enterokinase light chain
3. Incubate at 25°C for 16 hours

1. Enterokinase is inhibited by high salt concentrations. For optimal activity NaCl concentration should be 50 mM or less. The pH of the buffer should be between 6 and 9. The enzyme requires 2 mM Calcium for activity.