Showing papers on "Mimosine published in 1995"

Leucaena toxicosis and its control in ruminants

Abstract: Leucaena (Leucaena spp., especially L. leucocephala) is an arboreal, tropical legume that ranges into the cool subtropics and equatorial elevations up to 1,000 m. One of its uses includes forage for livestock, but introduction of leucaena outside its indigenous range often has led to acute and chronic toxicosis. The major toxic constituents of leucaena are the nonprotein free amino acid mimosine and its ruminal degradation product, 3-hydroxy-4(1H)-pyridone (3,4-dihydroxypyridine; 3,4-DHP). Leucaena also contains appreciable quantities of condensed tannins. In ruminants, mimosine is a depilatory agent and 3,4-DHP is a potent goitrogen. In the 1980s, Australian workers demonstrated that the geographical limits of leucaena toxicosis were due to the absence of ruminal bacteria capable of degrading 3,4-DHP, and successfully introduced 3,4-DHP degrading ruminal bacteria from a Hawaiian goat into goats and cattle in Australia. Simple in vitro screening methods have been developed for detection of 3,4-DHP degraders in ruminal samples and feces. Also, several strains of 3,4-DHP degrading ruminal bacteria have been characterized and have been given the genus and species designation, Synergistes jonesii. Ruminal inoculation with ruminal contents from adapted animals, enriched cultures of 3,4-DHP-degrading ruminal bacteria, and pure cultures of S. jonesii have all been used successfully to establish ruminal populations that are capable of degrading 3,4-DHP and preventing leucaena toxicosis. Once established in only a few animals, 3,4-DHP degraders easily distribute themselves throughout a herd of cattle and persist while leucaena is a component of the diet. After leucaena is removed from the diet, 3,4-DHP degraders continue to persist at reduced numbers for several months. With the availability of viable approaches to the control of leucaena toxicosis in ruminants, leucaena's potential as a high-quality perennial legume for the tropics and subtropics can be more fully exploited

Mimosine, a novel inhibitor of DNA replication, binds to a 50 kDa protein in Chinese hamster cells

Abstract: We recently demonstrated that the plant amino acid, mimosine, is an extremely efficacious inhibitor of DNA replication in mammalian cells [P. A. Dijkwel and J. L. Hamlin (1992) Mol. Cell. Biol. 12, 3715-3722; P. J. Mosca et al. (1992) Mol. Cell. Biol. 12, 4375-4383]. Several of its properties further suggested that mimosine might target initiation at origins of replication, which would make it a unique and very useful inhibitor for studying the regulation of DNA synthesis. However, mimosine is known to chelate iron, a cofactor for ribonucleotide reductase. Thus, the possibility arose that mimosine functions in vivo simply by lowering intracellular deoxyribonucleotide pools. In the present study, we show that, in fact, it is possible to override mimosine inhibition in vivo by adding excess iron; however, copper, which is not a substitute for iron in ribonucleotide reductase, is equally effective. Evidence is presented that mimosine functions instead by binding to an intracellular protein. We show that radiolabeled mimosine can be specifically cross-linked to a 50 kDa polypeptide (termed p50) in vitro. Binding to p50 is virtually undetectable in CHO cells selected for resistance to 1 mM mimosine, arguing that p50 is the biologically relevant target. p50 is not associated with the cellular membrane fraction and, hence, is probably not a channel protein. Furthermore, the binding activity does not vary markedly as a function of cell cycle position, arguing that p50 is not a cyclin. Finally, both iron and copper are able to reverse the mimosine-p50 interaction in vitro, probably explaining why both metal ions are able to overcome mimosine's inhibitory effect on DNA synthesis in vivo.

Mimosine is a potent clastogen in primary and transformed hamster fibroblasts but not in primary or transformed human lymphocytes.

Abstract: The cytogenetic effects of mimosine, a naturally occurring plant amino acid known to arrest cell-cycle progression at the G 1 -S border in cultured cells, have been studied. It was found that mimosine inhibits the cell-cycle progression in a dose-dependent manner in primary and transformed Chinese hamster fibroblasts as well as primary lymphocytes and transformed lymphoblastoid cells of human origin. In the Chinese hamster fibroblast cells, the first division metaphases analysed were found to be highly damaged or pulverized. The damaged cells which could pass through the next cell division, showed very high frequencies of sister chromatid exchanges (SCEs) compared with untreated second division cells. No such cytogenetic alterations could be detected in the human cells. The absence of clastogenic effect in cells of lymphoid origin appears to be related to the known capacity of these cells to undergo apoptosis, thereby efficiently eliminating cells with high frequencies of chromosomal aberrations. Our study demonstrates the clastogenic potency of mimosine and suggests the need for a careful interpretation of the results while using mimosine for cellular or molecular studies pertaining to cell cycle events.

Technical note: tissue residues of mimosine and 2,3-dihydroxypyridine after intravenous infusion in goats.

Abstract: Sixteen growing Alpine wethers (average BW 35±2 kg) were assigned to one of four treatments to evaluate tissue retention of the leucaena toxins mimosine (MIM) and 2,3-dihydroxypyridine (2,3-DHP). Treatments were infused i.v. for 2 d and were 1) saline control, 2) MIM (200 mg-kg BW -.75 -d -1 ), 3) 2,3-DHP (200 mg-kg BW -.75 -d -1 ), or 4) MIM (100 mg-kg BW -.75 -d -1 ) +2,3-DHP (100 mg-kg BW -.75 -d -1 ). Immediately after the infusion, the goats were slaughtered and tissue concentrations of MIM and 2,3-DHP were determined via HPLC. No detectable levels of either toxin were found in spleen, heart, lung, or muscle; however, appreciable amounts of MIM and 2,3-DHP were found in plasma, kidney, and liver samples. Kidney MIM content was greater (P .05). Infusion of MIM resulted in a plasma MIM content of 39 to 54 μmol/L and reduced (P<.01) plasma PHE and LEU. Infusion of 2,3-DHP resulted in a plasma 2,3-DHP content of 9.4 μmol/L and increased plasma THR, ARG, VAL, PHE, ILE, LEU, and LYS concentrations (P<.10). Humans consuming offals from ruminants consuming large amounts of the leguminous forage leucaena may be exposed to appreciable quantities of MIM and 2,3-DHP

Analysis of Leucaena mimosine, Acacia tannins and total phenols by near infrared reflectance spectroscopy

Abstract: The mimosine contents of Leucaena foliage, Acacia tannins and total phenols from leaf, bark and pod were analyzed by a near infrared reflectance spectrophotometer (Compscan 3000). A calibration equation (linear summation regression) was developed with near infrared spectral analysis software, using 30 spectra from old and young leaves of Leucaena and 23 spectra from different samples of Acacia . Each constituent required four wavelengths, i.e. Leucaena mimosine 1901, 2071, 2227 and 2234 nm; Acacia total phenols 1914, 2066, 2179 and 2183 nm; and tannins 2152, 2178, 2183 and 2295 nm, to derive the best calibration equation with first derivative instrument maths (segment 5 and gap 15). The near infrared analyzer calculated that the percentages of mimosine, total phenols and tannins are closely comparable to laboratory results.

Dissociation of p34cdc2 complex formation from phosphorylation and histone H1 kinase activity.

Abstract: The cell cycle inhibitor mimosine was used to examine the activation of the p34cdc2 protein kinase in S phase of the cell cycle. Addition of mimosine to cycling epithelial cells halted cell cycle traverse in S phase, coincident with an inhibition of p34cdc2 histone H1 kinase activity. Mimosine treatment did not alter p34cdc2 synthesis or turnover; however, overall phosphorylation of p34cdc2 was decreased to near undetectable levels. Although activity of p34cdc2 was inhibited, the ability of the protein to form high molecular weight complexes, a phenomenon associated with kinase activation in vivo , was not affected. These results indicate that p34cdc2 complex formation can occur in the absence of phosphorylation and that phosphorylation of p34cdc2 is then required to activate these preformed complexes.