Urokinase Activation of Plasminogen and Spontaneous Inactivation of the Plasmin Formed

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Abstract
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.