Inhibits both chymotrypsin and trypsin. Heterogeneous tetramers of similar chains. Mechanical damage (i.e. insect chewing) to this plant results in the systemic release of a factor from the wound site. Within the leaves it induces the cytoplasmic synthesis of proteinase inhibitors I and II. Belongs to the protease inhibitor I13 (potato type I serine protease inhibitor) family.