 Amatoxins belong to a family of bicyclic octapeptide derivatives composed of an amino acid ring bridged by a sulfur atom and characterized by differences in their side groups; these compounds are responsible for more than 90% of fatal mushroom poisonings in humans.The amatoxins inhibit the enzyme RNA polymerase II, which copies the genetic code of DNA into messenger RNA molecules.The toxin naturally accumulates in liver cells, and the ensuing disruption of metabolism accounts for the severe liver dysfunction cause by amatoxins.