![Illustration Ricinus communis0](https://upload.wikimedia.org/wikipedia/commons/7/73/Illustration_Ricinus_communis0.jpg)
Toxalbumins are toxic plant
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
s that disable
ribosomes and thereby inhibit
protein synthesis, producing severe
cytotoxic effects in multiple organ systems. They are
dimers held together by a
disulfide bond
In biochemistry, a disulfide (or disulphide in British English) refers to a functional group with the structure . The linkage is also called an SS-bond or sometimes a disulfide bridge and is usually derived by the coupling of two thiol groups. In ...
and comprise a
lectin (carbohydrate-binding protein) part which binds to the cell membrane and enables the toxin part to gain access to the cell contents. Toxalbumins are similar in structure to
AB toxin
The AB toxins are two-component protein complexes secreted by a number of pathogenic bacteria, though there is a pore-forming AB toxin found the eggs of a snail. They can be classified as Type III toxins because they interfere with internal cell ...
s found in
cholera,
tetanus
Tetanus, also known as lockjaw, is a bacterial infection caused by ''Clostridium tetani'', and is characterized by muscle spasms. In the most common type, the spasms begin in the jaw and then progress to the rest of the body. Each spasm usually ...
,
diphtheria
Diphtheria is an infection caused by the bacterium '' Corynebacterium diphtheriae''. Most infections are asymptomatic or have a mild clinical course, but in some outbreaks more than 10% of those diagnosed with the disease may die. Signs and s ...
,
botulinum
Botulinum toxin, or botulinum neurotoxin (BoNT), is a neurotoxic protein produced by the bacterium ''Clostridium botulinum'' and related species. It prevents the release of the neurotransmitter acetylcholine from axon endings at the neuromusc ...
and others; and their physiological and toxic properties are similar to those of
viperine snake venom.
Toxalbumins were first described in about 1890 by Ludwig Brieger (1849–1919) and
Sigmund Fraenkel Sigmund Fraenkel or Sigmund Fränkel (22 May 1868, in Krakau – 7 June 1939, in Geneva) was a Polish-born chemist who lived and worked in Austria, and is notable for being the head of the ''Ludwig-Spiegler-Stiftung'' in Vienna from 1904 and his wor ...
(1868–1939), associates of the organic chemist
Eugen Baumann
Eugen Baumann (12 December 1846 – 3 November 1896) was a German chemist. He was one of the first people to create polyvinyl chloride (PVC), and, together with Carl Schotten, he discovered the Schotten-Baumann reaction.
Life
Baumann was born i ...
. Brieger first used the term
toxin
A toxin is a naturally occurring organic poison produced by metabolic activities of living cells or organisms. Toxins occur especially as a protein or conjugated protein. The term toxin was first used by organic chemist Ludwig Brieger (1849 ...
.
Toxalbumins notably are present in the plant families
Leguminosae and
Euphorbiaceae
Euphorbiaceae, the spurge family, is a large family of flowering plants. In English, they are also commonly called euphorbias, which is also the name of a genus in the family. Most spurges, such as '' Euphorbia paralias'', are herbs, but some, ...
, occurring for instance in ''
Robinia pseudoacacia
''Robinia pseudoacacia'', commonly known in its native territory as black locust, is a medium-sized hardwood deciduous tree, belonging to the tribe Robinieae of the legume family Fabaceae. It is endemic to a few small areas of the United States, ...
'', ''
Abrus precatorius
''Abrus precatorius'', commonly known as jequirity bean or rosary pea, is a herbaceous flowering plant in the bean family Fabaceae. It is a slender, perennial climber with long, pinnate-leafleted leaves that twines around trees, shrubs, and hedge ...
'', ''
Jatropha curcas
''Jatropha curcas'' is a species of flowering plant in the spurge family, Euphorbiaceae, that is native to the American tropics, most likely Mexico and Central America. It is originally native to the tropical areas of the Americas from Mexico t ...
'', ''
Croton gratissimus'' and ''
Ricinus communis
''Ricinus communis'', the castor bean or castor oil plant, is a species of perennial flowering plant in the spurge family, Euphorbiaceae. It is the sole species in the monotypic genus, ''Ricinus'', and subtribe, Ricininae. The evolution of cas ...
''. Typical toxalbumins are
abrin
Abrin is an extremely toxic toxalbumin found in the seeds of the rosary pea (or jequirity pea), ''Abrus precatorius''. It has a median lethal dose of 0.7 micrograms per kilogram of body mass when given to mice intravenously (approximately 3 ...
and
ricin. Ingestion of seed containing toxalbumins is not necessarily fatal as the hard seed coat will withstand digestion, unless the seed has been pierced, as would happen in the making of necklaces, prayer beads or bracelets, and even then the toxalbumin is likely to be digested and thereby rendered harmless. Toxalbumins injected intravenously or subcutaneously or inhaled in powdered form, though, are highly toxic. A latent period of hours to days may follow with no sensible signs of distress, after which symptoms of nausea, vomiting and diarrhoea will appear, followed by delirium, seizures, coma, and death. From an evolutionary viewpoint, toxalbumins developed as a deterrent to consumption of seeds, foliage, bark and roots. Ripe fruits having a fleshy pulp are usually tasty and edible and lacking toxalbumins, encourage ingestion and the consequent distribution of seeds that have a coat sufficiently durable to survive a passage through the digestive system of a herbivore or fructivore.
Being soluble in water, ricin is not present in extracted oils. As with most proteins it breaks down after heat treatment, such as cooking or steaming, and after the oil is extracted, the resulting pomace is often used as animal feed. There is an enormous variation in sensitivity to the toxin, and a lethal dose may be as little as two-millionths of body weight. Since ricin is a protein, antibodies may be produced by inoculation, allowing resistance of up to 800 times a normal lethal dose. Ricin has been used in assassinations, a notorious case being the use of a 1.53 mm pellet holding a few hundred millionths of a gram of ricin to kill the Bulgarian broadcaster,
Georgi Markov
Georgi Ivanov Markov ( bg, Георги Иванов Марков ; 1 March 1929 – 11 September 1978) was a Bulgarian dissident writer. He originally worked as a novelist, screenwriter and playwright in his native country, the People's Repub ...
, who died 4 days after being attacked.
Compared to amatoxins
The toxins present in poisonous mushrooms such as ''
Amanita phalloides
''Amanita phalloides'' (), commonly known as the death cap, is a deadly poisonous basidiomycete fungus, one of many in the genus ''Amanita''. Widely distributed across Europe, but now sprouting in other parts of the world, ''A. phalloides ...
'' are quite different from toxalbumins and are mostly
secondary metabolites
Secondary metabolites, also called specialised metabolites, toxins, secondary products, or natural products, are organic compounds produced by any lifeform, e.g. bacteria, fungi, animals, or plants, which are not directly involved in the nor ...
or
amatoxins Amatoxin is the collective name of a subgroup of at least nine related toxic compounds found in three genera of poisonous mushrooms (''Amanita'', ''Galerina'' and ''Lepiota'') and one species ( Conocybe filaris) of the genus '' Conocybe''. Amatoxins ...
which do not readily break down under applied heat. They are potent inhibitors of
RNA polymerase II
RNA polymerase II (RNAP II and Pol II) is a multiprotein complex that transcribes DNA into precursors of messenger RNA (mRNA) and most small nuclear RNA (snRNA) and microRNA. It is one of the three RNAP enzymes found in the nucleus of eukaryo ...
, an enzyme vital in the synthesis of
messenger RNA (mRNA),
microRNA
MicroRNA (miRNA) are small, single-stranded, non-coding RNA molecules containing 21 to 23 nucleotides. Found in plants, animals and some viruses, miRNAs are involved in RNA silencing and post-transcriptional regulation of gene expression. mi ...
, and
small nuclear RNA
Small nuclear RNA (snRNA) is a class of small RNA molecules that are found within the splicing speckles and Cajal bodies of the cell nucleus in eukaryotic cells. The length of an average snRNA is approximately 150 nucleotides. They are transcribe ...
(snRNA). Without mRNA, the template for protein synthesis, cell metabolism stops. In this respect, their metabolic effect is similar to that of toxalbumins.
External links
'Plant toxins and acute medicinal plant poisoning in children: A systematic literature review'
See also
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References
{{reflist
Plant proteins
Plant toxins
Poisons