There are many toxins produced by fungi of many different kinds, such as aflatoxin, a potent carcinogen which can contaminate food. (Some of these will be discussed in Chapter 10.) Fungi in the form of mushrooms can be eaten, but many fungi, including mushrooms and toadstools, produce potent toxins. Some of these are or have been used as drugs.
Probably the most poisonous mushroom in Britain is the death cap mushroom (Amanita phalloides), which is also found in other parts of the world (see Figure 19). It may occasionally be eaten by mistake, although poisoning with this mushroom is rare. The mushroom contains a number of toxins: several phallotoxins and several amatoxins. The phallotoxins produce violent gastroenteritis four to eight hours after the mushroom is eaten. The amatoxins have a delayed toxic effect, targeting the liver and kidneys, and causing destruction of the cells of both. After eating the mushroom one may experience few if any symptoms, apart from nonspecific effects like nausea, followed by vomiting and diarrhoea. There can be a phase of perhaps two days in which the victim seems to recover. However, he or she can then suffer liver and kidney failure, as indicated by jaundice and alterations in the chemistry of the blood, such as low levels of sugar in the blood and high levels of nitrogen containing waste products.
The amatoxins and phallotoxins are cyclic peptides (peptides are made
of groups of amino acids and are the building blocks of proteins). The phallotoxins act on the membranes of cells while the amatoxins, which are more potent, prevent the production of proteins from the information encoded in the DNA (this is the main function of DNA). About 10 mg of one of the amatoxins is sufficient to kill a human being.
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