Urokinase Activation of Plasminogen and Spontaneous Inactivation of the Plasmin Formed

Summary The kinetics of the activation of plasminogen into plasmin with urokinase and the inactivation rate of the plasmin formed are studied. As a first order reaction is obtained with low plasminogen concentrations and a zero-order reaction is obtained with high concentrations, the activation seems to follow the Michaelis-Menten’s law. The reaction does not go to completion, however. Different activity levels, which are dependent on the urokinase concentration, can be observed. The activation rate increases with temperature. A maximum can be seen at about 42° C. Between 4° C and 15° C, the inactivation of the plasmin formed is minimal, but it increases rapidly at higher temperatures. The inactivation follows approximately a first order reaction with respect to time. If the plasminogen concentration is low, the over-all reaction will be that of two consecutive first order reactions.