[Mechanism of thrombolytic enzymes]

Thrombolytic enzymes belong to plasminogen activator (PA) in blood fibrinolysis and love been used for the efficient thrombolysis is achieved by the administration of PA which has high affinity for fibrin and induces plasminogen activation on the fibrin surface. PA with lower affinity for fibrin can activate plasminogen in circulating plasma, which causes bleeding tendency. At present, 11 PAs which are available for clinical usage or under investigation, are classified into two types: direct-type PA and indirect-type PA. The former which cleaved plasminogen directly and produces plasmin, includes urokinase-type PA, tissue-type PA, single-chain u-PA, bat PA, mutant PA, hybrid PA, IgG carrying PA and bispecific monoclonal antibody. The latter has no biological function by itself and expresses PA activity after forming a complex with plasminogen. This group includes streptokinase, anisoylated plasminogen streptokinase activator complex and staphylokinase. The PA activity of staphylokinase/plasminogen complex is inhibited by alpha 2-plasmin inhibitor, but can be expressed on the fibrin surface. Thus, PA activity of this complex is hardly observed in plasma. These feature of staphylokinase resembles to tissue-type PA.