Identification of an Important Odorant Precursor in Durian: First Evidence of Ethionine in Plants.

On the basis of the following data from the literature, we hypothesized the presence of ethionine in durian pulp: (1) the major odorants in terms of quantity as well as odor potency in durian pulp are ethanethiol and its derivatives; (2) genome analysis of durian assigned methionine γ-lyase (MGL), the enzyme that converts methionine to methanethiol, a key role for durian odor formation; and (3) MGL accepts not only methionine but also ethionine as a substrate. A targeted search by liquid chromatography-tandem mass spectrometry allowed us to confirm the presence of ethionine in durian pulp. Quantitation of ethionine in samples of different varieties (Monthong, Krathum, Chanee, and Kanyao) showed concentrations (621-9600 µg/kg) in the same range but below the methionine concentrations (16100-30200 µg/kg). During fruit ripening, the ethionine concentration increased as well as the ethanethiol concentration. Final evidence for the role of ethionine as an ethanethiol precursor was provided by demonstrating the formation of (2H5)ethanethiol after adding (2H5)ethionine to durian pulp.

Intriguing cellular processing of a fluorinated amino acid during protein biosynthesis in Escherichia coli.

Bioincorporation of the methionine analogue S-(2-fluoroethyl)-l-homocysteine (l-MFE) into bacteriophage lysozyme overproduced in Escherichia coli results not only in the expected l-MFE incorporation but surprisingly substantial l-vinthionine incorporation into the labeled lysozymes. Synthetic l-vinthionine itself however is not activated by purified Escherichia coli methionyl-tRNA synthetase. The indirect preparation of vinthionine-containing proteins has the potential to be an alternate strategy to prepare vinyl thioether moieties for click chemistry applications on proteins.

Separation and determination of seleno amino acids using gas chromatography hyphenated with inductively coupled plasma mass spectrometry after hollow fiber liquid phase microextraction.

A new derivatization-extraction method for preconcentration of seleno amino acids using hollow fiber liquid phase microextraction (HF-LPME) was developed for the separation and determination of seleno amino acids in biological samples by gas chromatography-inductively coupled plasma mass spectrometry (GC-ICP-MS). Derivatization was performed with ethyl chloroformate (ECF) to improve the volatility of seleno amino acids. Parameters influencing microextraction, including extraction solvent, pH of sample solution, extraction time, stirring speed, and inorganic salt concentration have been investigated. Under the optimal conditions, the limits of detection (LODs) obtained for Se-methyl-selenocysteine (SeMeCys), selenomethionine (SeMet), and selenoethionine (SeEth) were 23, 15, and 11 ng Se l(-1), respectively. The relative standard deviations (RSDs) were 14.6%, 16.4%, and 19.4% for SeMeCys, SeMet, and SeEth (c = 1.0 ng ml(-1), n = 7), respectively, and the RSDs for SeMeCys, SeMet could be improved obviously if SeEth was utilized as the internal standard. The proposed method was applied for the determination of seleno amino acids in extracts of garlic, cabbage, and mushroom samples, and the recoveries for the spiked samples were in the range of 96.8-108% and 93.4-115% with and without the use of SeEth as internal standard. The developed method was also applied to the analysis of SeMet in a certified reference material of SELM-1 yeast and the determined value is in good agreement with the certified value.

Ethionine carcinogenesis in CD-1, BALB/c and C3H mice.

In two separate in vivo studies, ethionine was evaluated for carcinogenic activity in mice. In the first study, DL-ethionine was fed in a chow diet at 0 (controls), 0.1 (low dose, LD) and 0.25% (high dose, HD) concentrations to the following groups of mice (30 animals/group): Swiss Webster CD-1 females, BALB/c males, and C3H/HeN males and females. Because of severe toxicity, BALB/c females were fed 0.05% (LD) and 0.1% (HD) ethionine. The Swiss and BALB/c mice were maintained on their respective diets for up to 105 weeks before killing whereas the C3H mice were killed at 68 weeks because of the high spontaneous incidence of liver tumors in this strain. The percentages of animals at risk (surviving the time to the first liver tumor recorded in each sex and strain) that bore liver tumors were as follows: Swiss female control, 0% (0/29), Swiss female LD, 87% (20/23); Swiss female HD, 89% (16/18); C3H male controls, 35% (8/23); C3H male LD, 55% (16/29); C3H male HD, 58% (15/26); C3H female controls, 5% (1/20); C3H female LD, 60% (12/20); C3H female HD, 92% (12/13); BALB/c male controls, 4% (1/23); BALB/c male LD, 8% (2/24); BALB/c male HD, 31% (5/16); BALB/c female controls, 0% (0/30); BALB/c female LD, 52% (14/27); and BALB/c female HD, 92% (12/13). The female mice were more responsive than the males in developing liver tumors. The results of the feeding study are compared with those obtained in a second study in which C3H female mice were intubated with 0, 150 or 500 mg DL-ethionine/kg body wt three times per week for 30 weeks and killed at 2 years. Only the LD mice showed a significantly increased incidence of liver tumors (20/39) as compared to controls (12/41) or HD mice (7/37) in the latter study. The hepatic levels of the major ethionine metabolite and methylase inhibitor, S-adenosylethionine (AdoEt), as well as of the endogenous methyl group donor, S-adenosylmethionine (AdoMet) were determined in Swiss female mice fed either 0.1 or 0.3% in the diet for 1-6 weeks. Hepatic AdoEt levels ranged from 37 to 80 micrograms/g liver in the LD animals and from 61 to 203 micrograms/g liver in the HD group; levels of the endogenous metabolite AdoMet correspondingly dropped to 65% of the normal levels. The present results (i) extend to different strains and to both sexes previous observations demonstrating the hepatocarcinogenic activity of ethionine in mice; and (ii) indicate that as in the rat such activity may be exerted through the formation of AdoEt.

A rapid high-performance liquid chromatographic procedure for the simultaneous determination of methionine, ethionine, S-adenosylmethionine, S-adenosylethionine, and the natural polyamines in rat tissues.

A method for the analysis of S-adenosyl-L-methionine (SAM) and S-adenosyl-L-ethionine (SAE) and their major metabolites by high-performance liquid chromatography is described. The procedure allows the simultaneous analysis of the natural polyamines, putrescine, spermidine, and spermine, and some of the major amino acids, methionine, tyrosine, and tryptophan. The uv absorbance at 254 nm is used for the determination of the SAM and SAE analogs, whereas the polyamines and amino acids are analyzed by fluorescence detection after postcolumn derivatization with o-phthalaldehyde. The method allows SAM and polyamine determinations by direct injection of the tissue extracts without prepurification. The procedure is applied to study the effects of DL-ethionine treatment on the SAM, SAE, methionine, and polyamine levels in various tissues of rats.