Purification of liver serine protease which activates microsomal glutathione S-transferase: possible involvement of hepsin

Rat liver microsomal glutathione S-transferase (MGST1) is known to be activated by trypsin, however, it has not been clarified whether MGST1 is activated by a protease present in liver. In the present study we purified the MGST1 activating protease from liver microsomes and finally identified that the protease is hepsin, a type II transmembrane serine protease. When the protease was incubated with the purified MGST1 or liposomal MGST1 at 4 degrees C, MGST1 activity was increased 3-4.5 fold after 3-6 d. In electrophoretic and immunoblot analyses after the incubation of MGST1 with the protease MGST1 dimer and its degraded fragment were detected. These results suggest that the rat liver microsomal hepsin functions as MGST1 activating/degrading enzyme.