It is an amatoxin, all of which are found in several members of the mushroom genus Amanita.
The oral LD50 of amanullin is approximately 20 mg/kg in mice; however, it is non-toxic in humans.
Like other amatoxins, amanullin is an inhibitor of RNA polymerase II.
Amanullin has a species dependent and specific attraction to the enzyme RNA polymerase II.
Upon ingestion, it binds to the RNA polymerase II enzyme, effectively causing cytolysis of hepatocytes (liver cells).