[Kinetics of fibrin lysis by plasmin: inhibition by fibrin degradation products].

A kinetics of lysis of 125I-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 Km, the catalytic constant of the reaction of fibrinolysis by plasmin kcat, and the constant of inhibition by the reaction products Ki were determined to be 1.3 microM, 1.36 min-1, and 0.12 microM, 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.