The resistance of fibrin-stimulated tissue plasminogen activator to inactivation by a class PAI-2 inhibitor (minactivin).

Solid phase fibrin was an efficient stimulator of the tissue-type plasminogen activator (t-PA), and the plasmin produced could be detected by colorimetric assay of the soluble phase above the fibrin. However the fibrin-stimulated activity of t-PA was not inhibited by minactivin. This result was in contrast to that obtained with poly-D-lysine (PL) stimulated t-PA, where minactivin was a potent inhibitor. However, if PL was added to fibrin-bound t-PA, the enzyme once again became susceptible to minactivin inhibition. This occurred without release of t-PA from the fibrin matrix. Minactivin alone did not bind to fibrin or to the t-PA fibrin complex. It was therefore concluded that minactivin normally has no significant role in the regulation of t-PA mediated fibrinolysis, but this effect can be induced by PL.