The Mechanisms of the Activation of Plasminogen by Streptokinase and Urokinase
Plasminogen activation to plasmin is due to enzymatic cleavage of a single peptide bond in the zymogen molecule. These enzymes are called plasminogen activators. There are three categories in plasminogen activators: streptokinase (SK), urokinase (UK) and tissue plasminogen activators (t-PA). It has been well documented that the activation rate of plasminogen by t-PA was remarkably enhanced in the presence of fibrin, and this part is reported by A. Takada in this book. On the other hand, the role of fibrin in the activation of plasminogen by UK have been controversial (1–4). Studies from several laboratories showed that fibrin and its related substances enhance the activity of SK (5–10). It was claimed that fibrinogen increases only the rate of formation of an active site in the SK-plg complex and does not have an effect on the activator activity of the SK-plg complex (8). However, other studies (5, 9, 10) found that fibrinogen also stimulates the activator activity of the complex.
KeywordsPlasminogen Activator Tissue Plasminogen Activator Related Substance Clot Plasma Plasminogen Activation
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