Kinetics of glu- and lys-plasminogen activation by the tissue activator in a fibrin clot

Using a modified procedure for measuring the time of fibrin clot lysis, the kinetics of Glu- and Lys-plasminogen activation by the tissue activator was studied. Within the plasminogen concentration range of 0.4-100 nM the rate of activation of both protein forms obeys the Michaelis-Menten kinetics. At Lys-plasminogen concentration equimolar to that of fibrin, the rate of activation of the former decreases down to that of Glu-plasminogen activation. The kinetic constants for Glu- and Lys-plasminogen activation (Km) are equal to 0.055 and 0.013 microM; k = 0.19 and 0.21 s-1, respectively. The Km values for fibrin-bound Glu- and Lys-plasminogen are equal to 0.25 nM and 8 nM, respectively (k = 0.08 and 0.26 s-1, respectively). It is assumed that the tissue activator exhibits a higher affinity for the Glu-plasminogen--fibrin complex than for the Lys-plasminogen-fibrin complex.