Mimosine, toxicity

Murugesan, K. and Radha, A. (1994) Biochemical mechanism of mimosine toxicity to fungi. Int.. Trap. Plant Dis., 12,171-6. 

Leucaena spp. contain mimosine, which is degraded to 3-hydroxy-4(l//)-pyridone (3,4-DHP see Section 2.2.4 for more detail). Leucaena, while toxic to unadapted ruminants, is a good source of protein and minerals for many livestock species in some countries. However, if Leucaena is ingested as 50% or more of the diet it will depress growth, cause hair loss, and reduce reproductive performance. Mimosine is a toxin that animals may become adapted to. Ruminal adaptation can be transferred from animal to animal, suggesting a specific set of rumen organisms are capable of detoxifying this amine. 

The effects of leucaena and mimosine on nonruminants can be reduced to some extent by diet supplementation with ferrous sulfates. Mimosine forms a complex with iron, which is excreted in the feces. Zinc supplementation has reduced the toxicity in cattle and it is believed that copper and zinc ions bind more strongly to mimosine than most other amino acids. 

Some further toxic plant amino acids include the jV-methylpyridinone mimosine (DNA binding and damaging) and 2-methylenecyclopropylalanine (hypoglycin) and 2-methyl-enecyclopropylglycine that, respectively, yield 2-methylenecyclopropylacetylCoA and... 

Mimosine (= Leucama leucocephala (jumbie bean), mutagenic, toxic, teratogenic] DNA - binding breakage by... 

Activity toxicity M. is a powerful inhibitor of cystathionine synthase and cystathionase. The growth of shoots of Phaseolus aureus is inhibited by 3,4-dihy-droxypyridine and mimosine with equal activity. The inhibitory activity is neutralised by addition of pyri-doxal phosphate. M. causes loss of hair in sheep, horses, and pigs goats and cattle, in contrast, are not affected in this way. M. effects growing hair, impairs the estrogen cycle in rats, and DNA synthesis. ... 

L-Mimosine (18) (Fig. 13.5) is a toxic heterocyclic amino acid that has been reported from several legumes. Among the plants that contain mimosine are Mimosa pudica and Leucaena leucocephala. The latter is often cultivated in tropical countries as a windbreak, a forage crop, and as a shade crop for coffee, tea and cacao (Rosenthal, 1991). This native of Mexico is capable of fixing nitrogen and is a quite agres-sive species. 

There are very few alkaloids present in wood (75, 152), but they are, of course, found extensively in plants (143, 187, 188). There were many instances of toxic alkaloids in the ancient literature. The most infamous example was the use of coniine from poison hemlock, Conium maculatum, to kill the greatest philosopher of all, Socrates. The hemlock woods of commerce Tsuga spp.) are not related to this species, and they do not contain coniine. Nowadays, more poisoning of livestock, rather than people, occurs as a consequence of alkaloid ingestion. Keeler (93) recently reviewed the many plant toxins and their effects on livestock. Various alkaloids from Magnolia spp. have been shown (152) to possess cytotoxic and antibacterial effects. There are several toxic non-protein amino acids, but only mimosine has been extracted from wood. The effects of this compound have been reported by Keeler (93). The comparative toxicity of some non-protein amino acids has been reviewed (70, 151). 

An important amino acid toxic to Hvestock is L-mimosine, P-(3-hydroxy-4-pyridone-l-yl)-L-alanine (see 2-62). It occurs in plants of genera Leucaena and Mimosa of the family Mimosaceae. Its quantity in the fodder plant L. leucocephala can reach up to 30-50 g/kg of dry matter. 

---