What does a-amanitin from the death cap mushroom inhibit?

α-Amanitin, a potent toxin found in the death cap mushroom (Amanita phalloides), specifically inhibits RNA polymerase II. This enzyme is crucial for the transcription of mRNA, which is essential for protein synthesis in eukaryotic cells. By inhibiting RNA polymerase II, α-amanitin disrupts the production of mRNA, leading to a cessation of protein synthesis. This mechanism is what makes the toxin so dangerous, as it can lead to cell death and ultimately organ failure, particularly in the liver.

RNA polymerase I and RNA polymerase III are responsible for synthesizing ribosomal RNA and transfer RNA, respectively, but are not affected by α-amanitin. DNA polymerase is involved in DNA replication and is also not inhibited by this compound. The specific action of α-amanitin on RNA polymerase II is what distinguishes it from other toxins and underscores its lethal potential in cases of mushroom poisoning.