Inhibitor of trypsin (serine protease). May protect the plant by inhibiting proteases of invading organisms (By similarity). Tubers. Not detected in root, stem, leaves or flower bud. Not induced by sucrose, methyl jasmonate or wounding. Causes an allergic reaction in human. Has a single chain structure. Belongs to the protease inhibitor I3 (leguminous Kunitz-type inhibitor) family. Was originally (PubMed:1391774 and PubMed:1515078) thought to be an aspartic proteinase inhibitor.