Kinetics of fibrinolysis by plasmin: Inhibition by the products of fibrin degradation

A kinetics of lysis of I-125-labeled fibrin coagulates by plasmin was studied. The strong competitive inhibition of fibrinolysis by the products of fibrin degradation was found. On the basis of the integral analysis of the complete kinetic curves of the fibrinolysis products accumulation, the Michaelis constant K-m, the catalytic constant of the reaction of fibrinolysis by plasmin k(cat), and the constant of inhibition by the reaction products K-i were determined to be 1.3 mu M, 1.36 min(-1), and 0.12 mu M, respectively. The results obtained showed that the efficiency of plasmin inhibition by the reaction products exceeds that of plasmin interaction with the substrate. Thus, the process of fibrinolysis is regulated by a negative feedback mechanism.