Promanullin is a cyclic nonribosomal peptide. It is an amatoxin, all of which are found in the mushroom genus Amanita.
Like other amatoxins, proamanullin is an inhibitor of RNA polymerase II. Promanullin has a 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).[1]