Production of the modified form of human plasminogen in the plasma activated by urokinase.

Plasminogen, a precursor of proteolytic enzyme plasmin which lyses thrombi in vivo, is postulated to be adsorbed onto fibrin and is converted into a modified form by plasmin. The properties of the modified form examined in vitro support this hypothesis. Nevertheless, it has been postulated that no conversion of native plasminogen into the modified form occurs in plasma, since alpha 2-plasmin inhibitor rapidly inactivates plasmin formed. However, we suggested production of the modified form in the "post-exercise" plasma. The present study was undertaken to examine production of the modified form in a simpler system, urokinase-activated plasma. The amount of the modified form in the plasma was estimated using the previous method with modification, epsilon-aminocaproic acid-containing polyacrylamide gel disc electrophoresis. The amount in the post-exercise plasma was also re-estimated by the present method. The amount of the modified form increased with the increase in urokinase concentration added to plasma. The presence of the modified form in the post-exercise plasma was also confirmed. The modified form could be produced in the plasma where an excess amount of alpha 2-plasmin inhibitor was expected to exist. The present results indicate that conversion of native plasminogen into the modified form may occur in vivo, supporting the hypothesis mentioned above.