Amatoxins

Amatoxins are a subgroup of at least eight toxic compounds found in several genera of poisonous mushrooms, most notably Amanita phalloides and several other members of the genus Amanita, as well as some Conocybe, Galerina and Lepiota mushroom species.

Structure
The compounds have a similar structure, that of eight amino-acid rings; they were isolated in 1941 by Heinrich O. Wieland and Rudolf Hallermayer of the University of Munich. All amatoxins are oligopeptides synthesized as proproteins 34 or 35 amino acids long and then cleaved by a prolyl oligopeptidase

There are currently ten known amatoxins:

δ-Amanitin has been reported, but its chemical structure has not been determined.

Function
Their major toxic mechanism is the inhibition of RNA polymerase II, a vital enzyme in the synthesis of messenger RNA (mRNA), microRNA, and small nuclear RNA (snRNA). Without mRNA, essential protein synthesis, and hence cell metabolism, grind to a halt and the cell dies. The liver is the principal organ affected, as it is the organ which is first encountered after absorption in the gastrointestinal tract, though other organs, especially the kidneys, are susceptible. The RNA polymerase of Amanita phalloides is insensitive to the effects of amatoxins; as such, the mushroom does not poison itself.

Their swift intestinal absorption coupled with their thermostability explains why their toxic effects occur in a relatively short period of time. The most severe effects are toxic hepatitis with centrolobular necrosis and hepatic steatosis, as well as acute tubulointerstitial nephropathy, which altogether induce a severe hepatorenal syndrome (with a potentially fatal outcome).

The estimated minimum lethal dose is 0.1 mg/kg or 7 mg of toxin in adults.

Detection
Presence of amatoxins in mushroom samples may be detected by the Meixner Test (also known as the Wieland Test).