Serine protease inhibitor that is strongly active against trypsin (700 IU/mg) and moderately active against plasmin. Expressed by acrorhagi. Does not inhibit potassium channels (Kv), as well as metalloproteases, and cysteine proteases (papain and bromelain). Belongs to the venom Kunitz-type family. Sea anemone type 2 potassium channel toxin subfamily.