Activation pathway of glu-plasminogen to Lys-plasmin by urokinase.

When Glu-plasminogen (Glu-plg) was incubated with plasmin for various time intervals, and the mixture was activated by urokinase (UK), the activation rate increased gradually as incubation time increased. The presence of fibrin not only enhanced the activation rate of Glu-plg but also that of proteolytically modified form to some extent. The results of SDS-PAGE indicated that the release of N-terminal peptides from Glu-plg or Glu-plasmin takes place gradually when the concentration of plg was about 1 microM, and that Glu-plasmin I of larger molecular weight is more slowly converted to Lys-plasmin than Glu-plasmin II of smaller molecular weight. The amounts of carbohydrate moieties on the heavy chain of plasmin may influence the release of N-terminal peptide from Glu-plasmin. Kinetic studies indicate that Lys-plasmin has smaller km than Glu-plasmin, thus the former being better enzymatically than the latter.