Amanitin is the most powerful poison found in Amanita mushrooms. Its lethal dose is only 0.1-0.3 mg/kg, meaning that only 10 mg will kill a 100 kg man.

Amanitin(alpha-amanitin, to be exact) has an unusually strong and specific attraction to the enzyme RNA polymerase II, so upon ingestion, the poison  binds to this enzyme, killing liver cells.


        Amanita phalloides(Death cup)                              



Other reference:

Berkow, Robert(editor)The Merck Manual 16th edition. 1992



                    Amanita muscaria