Ricin chain A (RTA) is a ribosome inactivating enzyme with a molecular weight of 32 kDa. RTA is normally linked by a disulfide bond to the galactose/N acetylgalactosamine binding lectin (34 kDa), also called the B chain or RTB. Together with RTB, RTA constitutes the heterodimeric cytotoxin Ricin (RCA 60) from Ricinus communis. This ricin, which is a type 2 RIP (ribosome inactivating protein) is among the most potent cytotoxins in nature. Ricin is highly toxic to animal cells and to a lesser extent to plant cells.