Actinidain (EC 3.4.22.14, actinidin, Actinidia anionic protease, proteinase A2 of Actinidia chinensis) is a type of cysteine protease enzyme found in fruits including kiwifruit (genus Actinidia), pineapple, mango, banana and papaya. This enzyme is part of the papain-like peptidase C1 family.[1][2][3][4]
It is the primary allergen found in kiwifruit.[5] When ingested, actinidain works by cleaving tight junction proteins on the apical portions of intestinal epithelial cells.[1]
and commercially useful as a meat tenderizer.[6]