The Identification of (+)S-Methyl-L-cysteine Sulfoxide in Plants

Morris, Clayton J.; Thompson, John F.

doi:10.1021/ja01589a028

Cited by 108 publications

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“…Artifactual production during the work-up procedure is conceivable (2), although this hypothesis has not been supported by our work (3). S-Methylcysteine sulfoxide, which may be a precursor of S-methylcysteine, is a natural constituent of food (4), and the free amino acid has also been detected in plants (5). Incorporation of the methylated amino acid in the biosynthesis of Hb has been proposed by Tornqvist et al (6) as a contributor to the background levels of S-methylcysteine.…”

Section: Hemoglobin Adductsmentioning

confidence: 99%

Identification of endogenous electrophiles by means of mass spectrometric determination of protein and DNA adducts.

Farmer

Bailey

Naylor

et al. 1993

Environ Health Perspect

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Monitoring exposure to alkylating agents may be achieved by quantitatively determining the adduct levels formed with nucleic acids and/or proteins. One of the most significant results arising from the application of this approach has been the discovery in control populations of "background" levels of alkylated nudeic acid bases or alkylated proteins, in particular hemoglobin (Hb). In the case of Hb, a wide variety ofsuch adducts have been detected and quantitated by mass spectrometric techniques, with methylated, 2-carboxyethylated, and 2-hydroxyethylated modifications being most abundant. Although the source of these alkylation products is unknown, both endogenous and exogenous sources may be proposed. We have recently confirmed the presence of the N-terminal hydroxyethylvaline adduct in control human Hb using tandem mass spectrometry (MS-MS) and have now established background levels using GC-MS in more than 70 samples. Smoking raises the levels of the adduct up to 10-fold and occupational exposure to ethylene oxide up to 300-fold.Background levels of alkylated nucleic acids may be studied by analysis ofN7-alkylated guanine or N3-alkylated adenine, which are excised from nucleic acids after their formation and are excreted in urine. Although the presence of some of these urinary constituents may be accounted for by their natural occurrence in RNA or diet, the endogenous or exogenous source ofothers is unknown. Quantitative methods using MS-MS have now been developed for five ofthe observed urinary alkylguanines [N7-methyl-, N2-methyl-, N2-dimethyl-, N7-(2-hydroxyethyl)-, and N2-ethylguanine]. A GC-MS method has also been developed to measure urinary thymine glycol as a possible monitor of oxidative DNA damage.

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Section: Hemoglobin Adductsmentioning

confidence: 99%

Identification of endogenous electrophiles by means of mass spectrometric determination of protein and DNA adducts.

Farmer

Bailey

Naylor

et al. 1993

Environ Health Perspect

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“…These results showed no appreciable incorp:ration (e.g. rnethy-lcy-steine anId its suilfoxi(le have the L-coinfigturationi (8,19) The cvidence that cystine is an efficient prec;lrsor ofi methylcysteine suilfoxide suiggests that methvlcysteile is forni c(l lby methylation of cysteine.…”

Section: Resultsmentioning

confidence: 88%

Biosynthesis of S-Methylcysteine in Radish Leaves¹

Thompson

Gering²

1966

Plant Physiol.

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Summary. Investigationl on the biosynthesis of S-methyl-L-cysteine in radish leaves has shown that it is formed by the methylation of cysteine. This conclusioii is based on: A) the relatively high recovery of radioactivity in methylcysteine sulfoxide after the administration of cysteine or methyl-labeled methionine to radish leaves; B) the nearly complete recovery of label from methyl-labeled methionine in the methyl group of methylcysteine sulfoxide; and C) the similarity in the ratio of tritium to 14C in methylcysteine sulfoxide and in its methyl group to this ratio in the methyl group of methionine given to radish leaves. Direct evidence for the synthesis of methylcysteine in radishes was obtained for the first time.Conclusive evidence against the formation of methylcysteine from serine and a thiomethyl group from methionine as stuggested for garlic was the more efficient incorporation of the methyl group of methionine as compared to the sulfur atom into methylcysteine suilfoxide.S-Methyl-L-cysteine has been shown to be a nattural constituent of kidney bean seed (19) and . It is the putative precursor of methylcysteine sulfoxide (1) in crucifers. Wolff, Black and Downey (22) showed that methylmercaptan and serine were combined in the presence of yeast enzymes to form S-methylcysteine (equation I). CH3SH + CH2OHCHNH.,COOH -CH,SCH2CHNHXCOOH + H2O (I).More recently, Sugii and coworkers (15) have observed a high recovery of radioactivity in methylcysteine sulfoxide after feeding sulfuir labeled methionine to a garlic plant. The interpretation of this finding was that methylmercaptan was formed from methionine in garlic as in the rat (4) and that the methylmercaptan was then combined with serine as in the yeast system to form methylcysteine.In this paper, evidence is presented which indicates that S-methylcysteine is formed in radishes by methylation of cysteine. Materials and MethodsMethyl labeled methionine and unlabeled S-adenosylmethionine were obtained from Cal Biochem2. Method of Administrationt of Labeled and Unlabeled MIaterials to Radish Leaves. In order to carry out the studies described in this paper, it was necessary to have a method of getting quantitative uptake of radioactive compounds in a relatively short time, while simultaneously stupplying unlabeled compoulnds and preventing the leaf from wilting. The latter 2 problems were solved by the tuse of a collar around the petiole (fig 1). The handling of leaves and administration of labeled and unlabeled compouinds were carried out by the following procedures.An intact radish plant was dtug uip and immersed in water. The leaves were excised with a razor blade under water, rinsed, and transferred to distilled water. An alternative method which was not as reliable but saves plants was also employed. In the latter case, the leaves were excised withott tunearthing the plant and the entire petiole immediately immersed in distilled water. Any leaves which remained turgid after 4 to 6 hours at room temperature were used.The petiole was cleanied of any small ...

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“…It has been reported that S-methylcysteine and its sulphoxide are present in plants (Morris & Thompson, 1956), bacteria (Grabow & Smit, 1967) and other fungi (Ragland & Liverman, 1956) although the role of these compounds in metabolism is not understood. The synthesis of S-methylcysteine from cysteine and methyltetrahydrofolate (methyl-THF) would result in the regeneration of tetrahydrofolate (THF).…”

Section: Discussionmentioning

confidence: 99%

“…(1) Many y-glutamyl peptides have been isolated from plant (Morris & Thompson, 1956), animal (Kanazawa, Katimoto, Nakajima & Sano, 1965) and fungal (Morton & Broadbent, 1955) sources. y-Glutamyltranspeptidase activity has been demonstrated in animal tissues (Hanes, Hird & Isherwood, 1950) and in fungi (Waelisch, 1952).…”

Section: Discussionmentioning

confidence: 99%

Sulphur Metabolism of Puccinia graminis f.sp. tritici in Axenic Culture

Howes

Scott

1973

Journal of General Microbiology

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SUMMARYAxenic cultures of Puccinia graminis f. sp. tritici cannot reduce sulphate for sulphur-amino-acid synthesis. Although [35S]sulphide is incorporated into these amino acids, the fungus still has a nutritional requirement for a sulphur amino acid. Most of the incorporated sulphide was found in the culture filtrate in the form of cysteine, S-methylcysteine, glutathione and cysteinylglycine. There were appreciable amounts of labelled methionine in mycelial protein but very little of this amino acid appeared in the culture filtrate. The results indicate that the nutritional requirements for sulphur amino acids by the rust fungus is caused by loss of cysteine and some of its derivatives into the medium.

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The Identification of (+)S-Methyl-L-cysteine Sulfoxide in Plants

Cited by 108 publications

References 0 publications

Identification of endogenous electrophiles by means of mass spectrometric determination of protein and DNA adducts.

Identification of endogenous electrophiles by means of mass spectrometric determination of protein and DNA adducts.

Biosynthesis of S-Methylcysteine in Radish Leaves¹

Sulphur Metabolism of Puccinia graminis f.sp. tritici in Axenic Culture

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The Identification of (+)S-Methyl-L-cysteine Sulfoxide in Plants

Cited by 108 publications

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Identification of endogenous electrophiles by means of mass spectrometric determination of protein and DNA adducts.

Identification of endogenous electrophiles by means of mass spectrometric determination of protein and DNA adducts.

Biosynthesis of S-Methylcysteine in Radish Leaves1

Sulphur Metabolism of Puccinia graminis f.sp. tritici in Axenic Culture

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Biosynthesis of S-Methylcysteine in Radish Leaves¹