Alpha-Amanitin is a cyclic peptide of eight amino acids. It is possibly the most deadly of all the amatoxins, toxins found in several species of the Amanita genus of mushrooms, one being the death cap (Amanita phalloides) as well as the destroying angel, a complex of similar species, principally A. virosa and A. bisporigera. It is also found in the mushrooms Galerina marginata and Conocybe filaris. The oral LD50 of amanitin is approximately 0.1 mg/kg. The structure of the polypeptide is atypical of most polypeptides, due to the branching of the amino acid chain. A cross bridge between 6-hydroxy-tryptophan and cysteine allows the formation of a second "inner loop," as seen in the diagram at right. The "outer loop" is formed by the normal peptide bond of the carboxyl terminus to the amino terminus of the peptide chain.
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