ADCs Toxins, alpha-Amanitin, a cyclic peptide, consisting of eight amino acids.The source of this specific alpha-Amanitin is fungal fermentation. By this production method the supply problems are solved. alpha-Amanitin is an inhibitor of RNA polymerase II (0.02 micrograms/ml). RNA polymerase I was also inhibited by the relatively high concentration of alpha-amanitin (IC50 = 100 micrograms/ml and IC70 = 750 micrograms/ml).