The purification and characterization of bovine enterokinase from membrane fragments in the duodenal mucosal fluid.

Bovine enterokinase has been purified from the mucosal fluid adhering to the intestinal wall. Enterokinase is predominantly present as membrane fragments which must be treated with Triton X-100 to release the enzyme. The purification resulted in a higher yield of enzyme in fewer steps and in less time than when mucosal cells were used. The properties of the enzyme in the fluid are identical with those found previously with the mucosal cell preparation (Liepnieks, J. J., and Light, A. (1979) J. Biol. Chem. 254, 1677-1683), but differ in the size of the subunits and in amino acid composition from the enzyme purified from intestinal contents (Anderson, L. E. Walsh, K. A., and Neurath, H. (1977) Biochemistry 16, 3354-3360). It is highly unlikely that the existence of isoenzymes could explain these differences. It is more likely that the enzyme isolated from the intestinal contents represents an extensively degraded form with retention of enzymatic activity.