Inhibitor of HGFAC (PubMed:9346890). Also inhibits plasmin, and plasma and tissue kallikrein (PubMed:9115294). Inhibits serine protease activity of TMPRSS13 (PubMed:20977675, PubMed:28710277). Inhibits serine protease activity of ST14/matriptase in vitro (PubMed:28710277).