Amatoxins

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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.[1] All amatoxins are oligopeptides synthesized as proproteins 34 or 35 amino acids long and then cleaved by a prolyl oligopeptidase[2]

File:Amatoxins generic strucuture.png
The backbone structure is the same in all the amatoxins with five groups determining the compound.

There are currently ten known amatoxins:[3]

Name R1 R2 R3 R4 R5
α-Amanitin NH2 OH OH OH OH
β-Amanitin OH OH OH OH OH
γ-Amanitin NH2 OH H OH OH
ε-Amanitin OH OH H OH OH
Amanullin NH2 H H OH OH
Amanullinic acid OH H H OH OH
Amaninamide NH2 OH OH H OH
Amanin OH OH OH H OH
Proamanullin NH2 H H OH H

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.[4] 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.[5] The RNA polymerase of Amanita phalloides is insensitive to the effects of amatoxins; as such, the mushroom does not poison itself.[6]

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).

See also

References

  1. Litten, W. (1975). "The most poisonous mushrooms". Scientific American. 232 (3): 90–101. PMID 1114308. Unknown parameter |month= ignored (help)
  2. H. E. Hallen, H. Luo, J. S. Scott-Craig, and J. D. Walton (2007). "Gene family encoding the major toxins of lethal Amanita mushrooms". Proceedings of the National Academy of Sciences USA. 104 (48): 19097–19101. doi:10.1073/pnas.0707340104.
  3. K. Baumann, K. Muenter, and H. Faulstich (1993). "Identification of structural features involved in binding of α-amanitin to a monoclonal antibody". Biochemistry. 32 (15): 4043–4050. doi:10.1021/bi00066a027.
  4. Karlson-Stiber C, Persson H (2003). "Cytotoxic fungi - an overview". Toxicon. 42 (4): 339–49. doi:10.1016/S0041-0101(03)00238-1. PMID 14505933.
  5. Benjamin.p217
  6. Horgen, Paul A. (1978). "The insensitivity of mushroom nuclear RNA polymerase activity to inhibition by amatoxins". Archives of Microbiology. 118 (3): 317–9. doi:10.1007/BF00429124. PMID 567964. Unknown parameter |coauthors= ignored (help)


da:Amatoxiner hr:Amatoksin it:Amatossine fi:Amatoksiini sv:Amatoxiner



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