Abstract
An antifibrinolytic activity was found in the supernatant of washed platelet suspension in the process of platelet aggregation induced by thrombin, ADP and 5-hydroxytryptamine. The antifibrinolytic activity was closely associated with inhibitors in platelets, which specifically inhibited plasmin but not inhibited other proteases such as urokinase, thrombin and trypsin. One casein unit of plasmin activity was inhibited by the inhibitors released from approximately 108 platelets during the aggregation with thrombin. By the activity staining analysis, it was found that there are two kinds of plasmin inhibitors with the molecular weights of ≅25, 000 and ≅17, 000. These two inhibitors were stable after the treatment of the inhibitors with acid or denaturants, though the inhibitor with higher molecular weight lost the activity by dithiothreitol- and heat-treatments and two inhibitors lost also the activity by alkali-treatment. These inhibitors have been purified from the supernatant of aggregated platelets by ammonium sulfate precipitation, ion exchange chromatography, gel filtration and affinity adsorption to plasmin.
