Mimosine or leucenol is a toxic non-protein amino acid chemically similar to

tyrosine -Tyrosine or tyrosine (symbol Tyr or Y) or 4-hydroxyphenylalanine is one of the 20 standard amino acids that are used by cells to synthesize proteins. It is a conditionally essential amino acid with a polar side group. The word "tyrosine" is ...

. It occurs in some ''

Mimosa ''Mimosa'' is a genus of about 600 species of herbs and shrubs, in the mimosoid clade of the legume family Fabaceae. Species are native to the Americas, from North Dakota to northern Argentina, and to eastern Africa (Tanzania, Mozambique, and ...

'' spp. (including '' M. pudica'') and all members of the closely related

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

Leucaena ''Leucaena'' is a genus of flowering plants in the mimosoid clade of the subfamily Caesalpinioideae of the family Fabaceae. It contains about 24 species of trees and shrubs, which are commonly known as leadtrees. They are native to the Americas ...

''. This compound, also known as leucenol, was first isolated from the seeds of '' Leucaena glauca'' Benth., and was later investigated by Adams and coworkers.

Properties

Mimosine melts with decomposition. The hydrochloride salt melts at 174.5–175.0 °C with decomposition; the hydrobromide decomposes at 179.5 °C, and the hydroiodide decomposes at 183–183.5 °C. Mimosine only forms monobasic acids, but the methyl ester forms a dihydrochloride, C₇H₉O₂N₂(COOMe)•2 HCl•½ H₂O, mp. 175–6 °C.

Biological effects

Mimosine arrests dividing cells in the late G1 phase by inhibiting DNA replication initiation. In

ruminant Ruminants are herbivorous grazing or browsing artiodactyls belonging to the suborder Ruminantia that are able to acquire nutrients from plant-based food by fermenting it in a specialized stomach prior to digestion, principally through microb ...

s, mimosine is degraded to 3,4- and 2,3-dihydroxypyridone (3,4- and 2,3-DHP). Although

toxic Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a subst ...

osis has occurred in

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

Papua New Guinea Papua New Guinea, officially the Independent State of Papua New Guinea, is an island country in Oceania that comprises the eastern half of the island of New Guinea and offshore islands in Melanesia, a region of the southwestern Pacific Ocean n ...

Africa Africa is the world's second-largest and second-most populous continent after Asia. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 20% of Earth's land area and 6% of its total surfac ...

and

Florida Florida ( ; ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders the Gulf of Mexico to the west, Alabama to the northwest, Georgia (U.S. state), Georgia to the north, the Atlantic ...

, it has not been recorded in any other

tropical The tropics are the regions of Earth surrounding the equator, where the sun may shine directly overhead. This contrasts with the temperate or polar regions of Earth, where the Sun can never be directly overhead. This is because of Earth's ax ...

and subtropical regions.

Goat The goat or domestic goat (''Capra hircus'') is a species of Caprinae, goat-antelope that is mostly kept as livestock. It was domesticated from the wild goat (''C. aegagrus'') of Southwest Asia and Eastern Europe. The goat is a member of the ...

s in

Burma Myanmar, officially the Republic of the Union of Myanmar; and also referred to as Burma (the official English name until 1989), is a country in northwest Southeast Asia. It is the largest country by area in Mainland Southeast Asia and ha ...

lost hair when fed a diet containing 50% of ''

''. Goats and

cattle Cattle (''Bos taurus'') are large, domesticated, bovid ungulates widely kept as livestock. They are prominent modern members of the subfamily Bovinae and the most widespread species of the genus '' Bos''. Mature female cattle are calle ...

Hawaii Hawaii ( ; ) is an island U.S. state, state of the United States, in the Pacific Ocean about southwest of the U.S. mainland. One of the two Non-contiguous United States, non-contiguous U.S. states (along with Alaska), it is the only sta ...

are able to degrade the 3,4-DHP ruminally. Tolerance might be related to the presence or absence of

microbe A microorganism, or microbe, is an organism of microscopic size, which may exist in its single-celled form or as a colony of cells. The possible existence of unseen microbial life was suspected from antiquity, with an early attestation in ...

s tolerant to mimosine and 3,4-DHP. It is known that at least Australian goats do not share the abilities of their Hawaiian counterparts. Bickel and Wibaut found in feeding experiments with rats and mice that leucenol is probably the toxic constituent of '' Leucaena glauca'' seeds, but they did not observe with these animals the loss of hair that seems to occur when these seeds are fed to cattle. Aung from Myanmar isolated the new subspecies of '' Klebsiella pneumoniae'' that can degrade mimosine. Besides, Moe Thida Htun, from Myanmar also found another new sub-species of Bacillus aureus that can degrade mimosine. Some

rhizobia Rhizobia are diazotrophic bacteria that fix nitrogen after becoming established inside the root nodules of legumes (Fabaceae). To express genes for nitrogen fixation, rhizobia require a plant host; they cannot independently fix nitrogen. I ...

are known to produce rhizomimosinase, which consumes pyridoxal 5′-phosphate to degrade mimosine into 3,4 dihydroxypyridine,

pyruvate Pyruvic acid (CH3COCOOH) is the simplest of the alpha-keto acids, with a carboxylic acid and a ketone functional group. Pyruvate, the conjugate base, CH3COCOO−, is an intermediate in several metabolic pathways throughout the cell. Pyruvic ...

, and

ammonium Ammonium is a modified form of ammonia that has an extra hydrogen atom. It is a positively charged (cationic) polyatomic ion, molecular ion with the chemical formula or . It is formed by the protonation, addition of a proton (a hydrogen nucleu ...

. A similar enzyme, mimosinase, is produced by ''

Leucaena leucocephala ''Leucaena leucocephala'' is a small fast-growing Mimosoideae, mimosoid tree native to southern Mexico and northern Central America (Belize and Guatemala) and is now naturalized throughout the tropics including parts of Asia. Common names inclu ...

''.

References

{{Reflist 2,3-Diaminopropionic acids 4-Pyridones Plant toxins Toxic amino acids

Properties

Biological effects

See also

References