Purification of a plasminogen activator inhibitor indistinguishable from alpha1-antitrypsin and an urokinase inhibitor in pregnancy plasma.

An inhibitor of urokinase present in increased concentrations in plasma during pregnancy was purified. The inhibitor was identified by its pronounced effect on urokinase-induced fibrinolysis as opposed to the absence of effect on fibrinolysis induced by a tissue plasminogen activator. The inhibitor progressively inactivated urokinase upon incubation and was found to be indistinguishable from alpha1-antitrypsin.