Nepenthesin (also spelled nepenthacin[1][2] or nepenthasin[3]) is an aspartic protease of plant origin that has so far been identified in the pitcher secretions of Nepenthes and in the leaves of Drosera peltata.
[13] The names cephalotusin, dionaeasin and droserasin have been proposed for similar aspartic endopeptidases originating from the carnivorous plant genera Cephalotus, Dionaea and Drosera, respectively.
[14] In the late 19th century, Sydney Howard Vines showed that the pitcher fluid from Nepenthes could digest protein in acidic conditions.
He suggested the plants were making a digestive enzyme, for which he proposed the name "nepenthin".
[15] In 1998, Kenji Takahashi's group purified protein from 30 liters of Nepenthesia distillatoria fluid, finding activity similar to that previously described, and reporting part of the nepenthesin amino acid sequence.