Leucaena leucocephala Lamk de

[From Greek, leukos = white and kephale = head]

Physical description: It is a small tree native to tropical America. Leaves: bip-innate, stipulate and consists of 4-8 pinnae, and 10-20 pairs of folioles. The folioles are oblong to lanceolate, 7 mm-12 mm long, and glaucous below. A petiolar gland is usually present on the first pinnae of the petiole. The flowers are white and organized in dense, globose, solitary, and long pediceled axillary heads which are

Synonymy: Leucaena glauca sensu Bth., Mimosa glauca L.

Common names: Lead tree, white popinac; petai cina, petaijawa (Malay); Santa Helena (Filipino).

2cm-5cm in diameter. The calyx is 5-lobed. The corolla consists of 5 narrow petals. The andrecium comprises of 10 conspicuous stamens. The fruits are linear pods, which are mem-branaceous, flat, acuminate, 12 cm x 1cm-18cm x 1.5 cm and arranged in conspicuous bunches. Each pod contains 10-20 little seeds which are glossy and brown (Figs. 154 & 155).

Pharmaceutical interest: The widespread use of Leucaena /eucocepha/a (Lamk.) de Wit as a tropical forage crop on account of its resistance and richness in protein, vitamin K and carotene, has been partly hampered because of the high amounts of mimo-sine it is abound with.

Mimosine: Mimosine is a non-protein amino acid (N-(3-alanyl)-3-hydroxy-4-pyridone) derived from lysine, which is responsible for the toxicity of several plants classified within the genera Mimosa and Leucaena. Mimosine reversibly blocks cell cycle

Fig. 154. Leucaena leucocephala (Lamk.) de Wit.
Fig. 155. Leucaena leucocephala (Lamk.) de Wit.

Uses: In Burma, a paste made from the leaves of Leucaena /eucocepha/a (Lamk.) de Wit is applied externally as an antidote for snake and insect bites. In Indonesia, the seeds are eaten to remove worms from the intestines and to treat diabetes. The leaves, pods and seeds are considered edible there. In Malaysia, a decoction of the seeds is drunk to expel intestinal worms, and to treat diabetes and hypertension. Malays and Filipinos drink a decoction of the roots to induce menses. In Taiwan, this plant is used as fodder. In India, the bark is used to assuage internal pain.

Fig. 156. Hypothetical mechanism of action by which mimosine blocks cell progression in G1: Mimosine added to the culture medium chelates iron in the medium which is therefore prevented from entering the cell (1). The rest of the mimosine enters the cell where it either binds to a mimosine binding protein (MBP) or chelates intracellular iron from iron-containing proteins such as ribonu-cleotide reductase (RR). The catalysis of the reduction (deoxygenation) of the ribose ring of ribonucleoside 5'-diphosphates (R5D) to yield 2'-deoxyribonucleoside 5'-diphosphates (2DR5D) in nucleotides by ribonucleotide reductase is inhibited because of iron chelat-ing by mimosine, hence blockage of cell division.

progression in mammalian cells cultured in vitro in phase G1 and is used as a synchronization agent. The precise mechanism by which mimosine disrupts cellular proliferation remains controversial, and it has also been suggested that it blocks cell cycle progression by chelating iron (Fe2+) from iron-dependent enzymes such as ribonucleotide reductase (Kulp KS et a/., 1996; Fig. 156). A single intragastric dose of mimosine to mice inhibits the intake of iodine 125 by the thyroid at the iodine-binding step (Hegarty MP etal., 1979).

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