The cytotoxin a-amanitin is a bicyclic octapeptide occurring in high concentrations in the deadly, poisonous mushroom Amanita phalloides. The primary cytopathogenicity of the amatoxins is the inhibition of RNA polymerase B (ribonuc1eosidetriphosphate:RNA nucleotidyltransferase, EC 2.7.7.6)\u00a0which is the enzyme that transcribes the precursor of mRNA. RNA polymerases B from higher eukaryotes are typically half-maximally inhibited by a-amanitin at a concentration of<\/p>\n

5 X10^{-9<\/sup>\u00a0M.<\/p>\n}

In a very detailed study, Cochet-Meilhac & Chambon (1974) demonstrated that the amatoxins bind to RNA polymerase B with a 1:1 stoichiometry, that the affinity of the toxin for the enzyme is very strong with an equilibrium association constant of 3.5 X 10^{-8<\/sup>\u00a0M-1<\/sup>\u00a0at 30 \u2103, and that the dissociation is very slow and highly dependent upon temperature and ionic strength. Subsequently, it was shown by Brodner & Wieland (1976), using a carbodiimidecondensation reaction of labeled amatoxin to calf thymus RNA polymerase B, that the 140-kilodalton subunit was a binding site for the amatoxins. Thus, it has been clearly shown that inhibition by a-amanitin is the result of a direct interaction of the toxin with RNA polymerase B.<\/p>\n}

The process of RNA synthesis catalyzed by DNA-dependent RNA polymerase is quite complex and may be described in several steps as follows: (a) formation of a stable binary complex with the DNA template; (b) RNA chain initiation; (c) translocation and elongation of the nascent RNA; (d) termination and dissociation of the RNA chain. Hence, there are a number of enzyme mechanisms which could possibly be specifically disrupted by a-amanitin. It has been shown that the binding of a-amanitin does not cause a dissociation of the DNA-RNA polymerase B binary complex or the dissociation of the DNA-enzymeRNA ternary complex (Cochet-Meilhac & Chambon, 1974). In the same study, direct evidence was given that the binding of a-amanitin was responsible for the inhibition of RNA chain elongation as catalyzed by RNA polymerase B. The inhibition of chain initiation was suggestedn by indirect experimentation, i.e., by a failure to detect pyrophosphate exchange which is presumably the reverse reaction of phosphodiester bond formation (Krakow & Fronk, 1969). Therefore, it was concluded by Cochet-Meilhac & Chambon (1974) that the binding of amatoxin to RNA polymerase B prevents the formation of phosphodiester bonds.<\/p>\n

Reference:<\/p>\n

Vaisius, A. C., & Wieland, T. (1982). Formation of a single phosphodiester bond by RNA polymerase B from calf thymus is not inhibited by. alpha.-amanitin. Biochemistry, 21(13), 3097-3101.<\/p>\n

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The cytotoxin a-amanitin is a bicyclic octapeptide occurring in high concentrations in the deadly, poisonous mushroom Amanita phalloides. The primary cytopathogenicity of the amatoxins is the inhibition of RNA polymerase …<\/p>\n","protected":false},"author":1,"featured_media":480,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[1],"tags":[110],"_links":{"self":[{"href":"https:\/\/www.creative-peptides.com\/blog\/wp-json\/wp\/v2\/posts\/479"}],"collection":[{"href":"https:\/\/www.creative-peptides.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.creative-peptides.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.creative-peptides.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.creative-peptides.com\/blog\/wp-json\/wp\/v2\/comments?post=479"}],"version-history":[{"count":1,"href":"https:\/\/www.creative-peptides.com\/blog\/wp-json\/wp\/v2\/posts\/479\/revisions"}],"predecessor-version":[{"id":481,"href":"https:\/\/www.creative-peptides.com\/blog\/wp-json\/wp\/v2\/posts\/479\/revisions\/481"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.creative-peptides.com\/blog\/wp-json\/wp\/v2\/media\/480"}],"wp:attachment":[{"href":"https:\/\/www.creative-peptides.com\/blog\/wp-json\/wp\/v2\/media?parent=479"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.creative-peptides.com\/blog\/wp-json\/wp\/v2\/categories?post=479"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.creative-peptides.com\/blog\/wp-json\/wp\/v2\/tags?post=479"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}