Binding Of Plasminogen And Vascular Plasminogen Activator To Fibrin And The Fibrin Alpha-Chain
Investigation of the mechanism of plasminogen activation in the presence of fibrin has shown that fibrin acts as a regulatory and catalytic surface for both the reaction between activator and fibrin and between activator and plasminogen. Plasminogen (mol wt 84,000) and vascular activator form stable complexes with fibrin. We have carried out studies to determine the location of these binding sites in the fibrin structure.METHODS: Human plasminogen (mol wt 84,000) was iodinated with 125-I and vascular plasminogen activator was partially purified from venous occlusion plasma by chromatography on lysine-Sepharose. Sepharose coupled fibrinogen, fibrin monomer, fragments E and D and isolated fibrin alpha chain were prepared and the interactions between plasminogen and vascular activator studied.RESULTS: Plasminogen (mol wt 84,000), plasmin and vascular activator each showed affinity for Sepharosebound fibrin monomer and fibrin alpha chain. In addition the affinity of the vascular activator for fibrinogen and fragment E was increased by treatment with thrombin.CONCLUSION: The alpha chain of fibrin brings together plasminogen activator and plasminogen in such a way as to produce plasminogen activation resulting in the early degradation steps of fibrin.