Chemical Modification of Carbohydrate Chain of a Thrombin-Like Serine Protease Isolated from the Venom of Agkistrodon Halys Brevicaudus Stejneger

We have studied the structure-function relationship of a thrombin-like serine protease isolated from the venom of Agkistrodon halys brevicaudus stejneger ［1 ― 4］ . The protease was a single chain glycoprotein, 18% of which was carbohydrate. Both the sugar composition and the glycosylated site were different from those of thrombin. The function of the carbohydrate chain of the isolated protease remains unknown. In this report, the enzymatic property of carbohydrate-modified protease was compared to intact protease in order to elucidate the function of the carbohydrate chain. The chemical modification of the vicinal hydroxy groups on carbohydrate was carried out using PDBAhydrazide. The intact protease released fibrinopeptide A, B and Bβ1 ― 42. The PDBA-modified protease formed fibrin clots; however, fibrinopeptide A was primarily released while fibrinopeptide B and Bβ1 ― 42 released only slightly. The result led us to propose that access of the fibrinogen Bβ chain to the catalytic site cleft was restricted by the modification of the carbohydrate chain. The carbohydrate chain played an important role in protease activity, especially through its interaction with the protease and macromolecular substrates, such as fibrinogen. The enzymatic characteristics distinct from those of thrombin may be derived from the structural difference of the carbohydrate moiety.