Serine protease inhibitor. The major targets of this inhibitor are plasmin and trypsin, but it also inactivates matriptase-3/TMPRSS7 and chymotrypsin. Forms protease inhibiting heterodimer with TMPRSS7. Expressed by the liver and secreted in plasma. Proteolytically cleaved at Pro-39 by both the prolyl endopeptidase FAP form and antiplasmin-cleaving enzyme FAP soluble form to generate mature alpha-2-antiplasmin. The disease is caused by variants affecting the gene represented in this entry. Belongs to the serpin family.