Role of urinary alpha1-antitrypsin in Padutin (kallikrein) inactivation

An inverse relationship between proteolytic activity in the presence of kallikrein 0.4 IU and urinary alpha1-antitrypsin concentration has been demonstrated. This protease inhibitor can directly inactivate kallikrein activity. The inhibition was abolished by removal of urinary alpha1-antitrypsin by trypsin-sepharose treatment. Inhibition could be reversed by addition of purified alpha1-antitrypsin. These effects could not be demonstrated with inter-alpha-trypsin inhibitor or alpha2-macroglobulin. The inhibitory effect of alpha1-antitrypsin on kallikrein activity should be taken into account in studies in which kallikrein activity is estimated.