Inhibitor of subtilisin. Inhibits moderately trypsin and chymotrypsin (serine proteases). May protect the plant by inhibiting proteases of invading organisms. Cortex of tuber. Belongs to the protease inhibitor I3 (leguminous Kunitz-type inhibitor) family. PubMed:16668362 postulates a moderate inhibition of serine proteases but the sequence homology points to a cysteine protease inhibitor.