Protease inhibitors and human plasmin: Interaction in a whole plasma system

Abstract

Using trace amounts of [ 125I]-plasminogen and conventional biochemical techniques, the distribution of the labeled zymogen amongst the various protease inhibitors was studied in whole plasma before and after activation with urokinase and streptokinase. A small percentage of the labeled enzyme was bound to α 2-macroglobulin while a majority was complexed to a component in plasma immunologically distinct from the well known human antiplasmins. The inhibitor was identified as α 2-antiplasmin and confirmed the existence of this antiprotease recently described by others. These data also suggest that the other antiplasmins may play a minor, yet important role in the regulation of plasmin activity under different physiological conditions.