α-Amanitin !

α-Amanitin is the toxin of mushrooms such as Amanita phalloides; it blocks RNA polymerase II and destroys liver cells.

Updated 2026-11-01

Key facts

It strongly inhibits RNA polymerase II, Pol III less and Pol I not at all.
Without mRNA synthesis, highly active cells (hepatocytes, renal tubule) die.
Enterohepatic circulation: the liver takes it up (OATP1B3 transporter), excretes it in bile and reabsorbs it, repeating the damage.
Typical course: gut symptoms at 6–24 h, apparent recovery, then liver failure at 2–4 days.

A bicyclic octapeptide with a tryptathionine bridge (tryptophan–cysteine) that makes it very stable to heat and digestion.
It contains unusual hydroxylated amino acids; it survives cooking, freezing and drying.
It binds the large Pol II subunit (RPB1) near the 'bridge helix' and stalls translocation.

Responsible for most deaths from eating wild mushrooms worldwide.
Management includes intensive support, measures to break enterohepatic circulation, silibinin or penicillin in some protocols, and liver transplantation in severe failure.
It is being studied linked to antibodies (conjugates) as a weapon against tumour cells.

Think of the answer, then tap the question to see it.

Which enzyme does α-amanitin inhibit?

RNA polymerase II (and to a lesser degree Pol III), which halts mRNA synthesis.

Why does Amanita poisoning mainly damage the liver?

Hepatocytes take up the toxin via OATP1B3 and recycle it through the enterohepatic circulation.

What timeline is typical of amatoxin poisoning?

Gastroenteritis hours later, a false recovery, then liver failure at 2–4 days.

Educational information, not medical advice. For any symptom, see a health professional.

Sources: Alpha-Amanitin (CID 9543442) (PubChem, NCBI, 2026) · Public domain; POLR2A: DNA-directed RNA polymerase II subunit RPB1 (human) (UniProt, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).

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Representative model, for educational purposes only.