Serine protease inhibitor that acts against trypsin (EC(50)=10 nM, Ki=5nM), and plasmin (EC(50)=200 nM, Ki=100 nM). Expressed by the venom gland. Does not inhibit serine proteases (chymotrypsin, elastase, kallikrein, and pepsin), cysteine protease (cathepsin G), and MMP (1, 3, 7, 8, 9, 10, 12, 13, and 14), as well as voltage-gated potassium channels (Shaker and rKv1.1/KCNA1). Belongs to the venom Kunitz-type family.