The course and prerequisites of Lys-plasminogen formation during fibrinolysis

Plasmin-catalyzed modification of the native plasma zymogen Glu1-plasminogen to its more reactive Lys78 form has been shown to be enhanced in the presence of fibrin. The aim of the present work has been to characterize the influence of fibrinopeptide release, fibrin polymerization, and plasmin cleavage of fibrin on the rate of Lys78-plasminogen formation. 125I-Labeled Glu1- to Lys78-plasminogen conversion was catalyzed by performed Lys78-plasmin, or by plasmin generated during plasminogen activation with tissue plasminogen activator or urokinase. The two forms of plasminogen were quantitated following separation by polyacrylamide gel electrophoresis in acetic acid/urea. Plasmin generated by plasminogen activator was monitored by a fixed-time amidolytic assay. The rate of Lys78-plasminogen formation was correlated, in separate experiments, to the simultaneous, plasmin-catalyzed cleavage of 125I-labeled fibrinogen or fibrin to fragments X, Y, and D. The radiolabeled components were quantitated after separation by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The results show that the formation of both bathroxobin-catalyzed des-A-fibrin and thrombin-catalyzed des-AB-fibrin leads to marked stimulation of Lys78-plasminogen formation, whereas inhibition of fibrin polymerization, with Gly-Pro-Arg-Pro, abolishes the stimulatory effect. The rate of Lys78-plasminogen formation varies markedly in the course of fibrinolysis. The apparent second-order rate constant of the reaction undergoes a transient increase upon transformation of fibrin to des-A(B) fragment X polymer and decreases about 10-fold to the level observed during fibrinogenolysis upon further degradation to soluble fragments Y and D.(ABSTRACT TRUNCATED AT 250 WORDS)