A new, direct-acting chymotrypsin-like fibrinolytic serine protease was purified from Petasites japonicus, a medicinal herb. The molecular mass of the discovered enzyme was estimated to be 40.0 kDa as determined using sodium dodecyl sulfate polyacrylamide gel electrophoresis, fibrin zymography, and gel filtration chromatography. The N-terminal sequence of the purified enzyme was determined to be GQEDHFLQVSLTSA. The proteolytic activity of the enzyme was found to be inhibited by serine protease inhibitors phenylmethylsulfonyl fluoride and 4-(amidinophenyl) methanesulfonyl fluoride. An assay of enzyme activity on fibrin plates revealed that it could hydrolyze the fibrin directly. The enzyme displayed a potent fibrin(ogen)olytic activity, hydrolyzing the Aα-, α-, and Bβ-subunits of the human fibrinogen. The enzyme prolonged activated partial thromboplastin time and had little effect on prothrombin time. It prevented carrageenan-induced thrombus formation in mouse tails and did not increase the bleeding time. Our findings indicate that the extracted enzyme we present here has the potential for clinical use as an agent for the treatment of thrombosis.
