Inhibitor of cathepsin D (aspartic protease). May also inhibit trypsin and chymotrypsin (serine proteases). Protects the plant by inhibiting proteases of invading organisms. Tubers, young leaves and flower bud. Not detected in root, stem or mature leaves. By methyl jasmonate and wounding; but not by sucrose. Has a single chain structure. Belongs to the protease inhibitor I3 (leguminous Kunitz-type inhibitor) family.