名称：重组牛EK, His
Synonyms：Enterokinase, Serine Protease 7, Transmembrane Protease Serine 15
Source：Escherichia coli.
Molecular Weight：Approximately 28 kDa, a single non-glycosylated polypeptide chain containing 241 amino acids，with 6 × His at C-terminus.
Quantity：100IU/250IU/1000IU
Unit Definition：One unit is defined as the amount of enzyme needed to cleave 50 μg of fusion protein in 16 hours to 95 % completion at 25 °C in a buffer containing 25 mM Tris-HCl, pH 7.6, 50 mM NaCl, and 2 mM CaCl2.
Physical Appearance：Sterile liquid.
Formulation：50 mM Tris-HCl, pH 8.0, 0.5 M NaCl and 50 % glycerol.
Endotoxin：Less than 1 EU/µg of rBoEKL, His as determined by LAL method.
Stability & Storage：Use a manual defrost freezer and avoid repeated freeze-thaw cycles.
- 6 months from date of receipt, -20 to -70 °C as supplied.
- 3 months, -20 to -70 °C under sterile conditions after opening.
Reference：1. Yuan LDandHua ZC. 2002. Protein Expr Purif, 25: 300-4.
2. Peng L, Zhong X, Ou J, et al. 2004. J Biotechnol, 108: 185-92.
3. Light AandJanska H. 1991. J Protein Chem, 10: 475-80.
4. Kubitzki T, Minor D, Mackfeld U, et al. 2009. Biotechnol J, 4: 1610-8.
Background：Enterokinase (EK) is an amino protease existing in duodenum of mammal and is involved in digestion. It consists of a disulfide-linked 82–140 kDa heavy chain which anchors enterokinase in the intestinal brush border membrane and a 35–62 kDa light chain which contains the catalytic subunit. Additionally, both of the chains are derived from a single precursor that is cleaved by a trypsin-like protease. EK can specially recognize the amino acid sequence DDDDK, and digest the peptide bond after the lysine residue. rEK was report to be more effective than nature EK in cleaving recombinant proteins. Furthermore, the light chain possesses the whole enzyme activity of EK. rBoEK has the highest activity than EK of other species and is used wildly in biochemical applications. rBoEK with 6 × His-tag binds with Ni2+ affinity chromatography and was designed for removing from digestion system.