Soybeans and radish leaves contain only one of the sulfonium diastereoisomers of S-adenosylmethionine

Creason, Gary L.; Madison, James T.; Thompson, John F.

doi:10.1016/s0031-9422(00)81092-4

Cited by 15 publications

(15 citation statements)

References 12 publications

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“…The remaining pericarp slices were placed on moist paper towel and incubated for 18-h at room temperature in the dark. The pericarp tissue, weighing 6.08 kg, was divided into 15 batches and stored at -80°C until homogenization.…”

Section: Methodsmentioning

confidence: 99%

S-Adenosylmethionine-Dependent Inactivation and Radiolabeling of 1-Aminocyclopropane-1-Carboxylate Synthase Isolated from Tomato Fruits

Satoh

Yang²

1988

Plant Physiol.

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l-Aminocyclopropane-l-carboxylic acid (ACC) synthase was partially purified from the homogenate of wounded tomato (Lycoperiscon escukntum Mill.) Ethylene is a plant hormone regulating many aspects of plant growth and development, such as seed germination, seedling elongation, fruit ripening, and tissue senescence (1,12). It has been established that ethylene is biosynthesized from methionine via SAM3 and ACC and that the rate-limiting step in ethylene biosynthesis is the conversion of SAM to ACC, catalyzed by ACC synthase (21). Since ACC synthase is rapidly turned over in plant tissues, the concentration of the enzyme in plant tissue is determined not only by the synthesis of the enzyme but also by its inactivation (8,20).Recently, Satoh and Esashi (18) reported that ACC synthase obtained from mung bean hypocotyls is inactivated by its substrate, SAM, during its catalytic action. Similar finding was independently reported in a meeting abstract by Boller (3) with ACC synthase isolated from tomato pericarp tissue. Since the half-life of ACC synthase in vivo was similar to that in vitro,

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Section: Methodsmentioning

confidence: 99%

S-Adenosylmethionine-Dependent Inactivation and Radiolabeling of 1-Aminocyclopropane-1-Carboxylate Synthase Isolated from Tomato Fruits

Satoh

Yang²

1988

Plant Physiol.

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“…(R,S)-AdoMet levels were undetectable in immature soybeans, soybean callus culture, radish leaves, yeast, and rat liver (13); an (R,S)/(S,S)-AdoMet ratio of 0.03 was found in mouse liver (14); whereas (R,S)-AdoMet was found to be only 3% of total AdoMet in rat brain (24). These low (R,S)-AdoMet levels are in contrast to those predicted based on the measured racemization rate indicating that ϳ20% of AdoMet should be in the R,S form in cells that maintain a steady state level of AdoMet (14).…”

mentioning

confidence: 95%

“…Defects in this repair enzyme in humans leads to the brain disorder L-2-hydroxyglutaric aciduria (10). A third example, the diastereomer of S-adenosylmethionine ((R,S)-AdoMet), forms spontaneously from (S,S)-AdoMet (11)(12)(13)(14) and is recognized by specific homocysteine methyltransferases in yeast and other organisms for conversion to the normal metabolites methionine and S-adenosylhomocysteine (15).…”

mentioning

confidence: 99%

“…Over time, however, AdoMet can degrade in several ways. Briefly, there is an intramolecular reaction that produces homoserine lactone and 5Ј-methylthioadenosine, a hydrolysis reaction that produces adenine and S-pentosylmethionine, and the racemization reaction described above that produces (R,S)-AdoMet (13,14,20). (R,S)-AdoMet forms from the inversion of the configuration of the sulfonium center of the molecule from S to R. The full extent of (R,S)-AdoMet toxicity is still unknown.…”

mentioning

confidence: 99%

“…Interestingly, (R,S)-AdoMet levels are low to undetectable in the several tissues that have been assayed (13,14,24). (R,S)-AdoMet levels were undetectable in immature soybeans, soybean callus culture, radish leaves, yeast, and rat liver (13); an (R,S)/(S,S)-AdoMet ratio of 0.03 was found in mouse liver (14); whereas (R,S)-AdoMet was found to be only 3% of total AdoMet in rat brain (24).…”

mentioning

confidence: 99%

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Homocysteine Methyltransferases Mht1 and Sam4 Prevent the Accumulation of Age-damaged (R,S)-AdoMet in the Yeast Saccharomyces cerevisiae

Vinci¹,

Clarke²

2010

Journal of Biological Chemistry

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The biological methyl donor S-adenosyl-L-methionine (AdoMet) is spontaneously degraded by inversion of its sulfonium center to form the R,S diastereomer. Unlike its precursor, (S,S)-AdoMet, (R,S)-AdoMet has no known cellular function and may have some toxicity. Although the rate of (R,S)-AdoMet formation under physiological conditions is significant, it has not been detected at substantial levels in vivo in a wide range of organisms. These observations imply that there are mechanisms that either dispose of (R,S)-AdoMet or convert it back to (S,S)-AdoMet. Previously, we identified two homocysteine methyltransferases (Mht1 and Sam4) in yeast capable of recognizing and metabolizing (R,S)-AdoMet. We found similar activities in worms, plants, and flies. However, it was not established whether these activities could prevent R,S accumulation. In this work, we show that both the Mht1 and Sam4 enzymes are capable of preventing R,S accumulation in Saccharomyces cerevisiae grown to stationary phase; deletion of both genes results in significant (R,S)-AdoMet accumulation. To our knowledge, this is the first time that such an accumulation of (R,S)-AdoMet has been reported in any organism. We show that yeast cells can take up (R,S)-AdoMet from the medium using the same transporter (Sam3) used to import (S,S)-AdoMet. Our results suggest that yeast cells have evolved efficient mechanisms not only for dealing with the spontaneous intracellular generation of the (R,S)-AdoMet degradation product but for utilizing environmental sources as a nutrient.Aging can be seen as the accumulation of damaged biomolecules over time (1-3). As such, understanding the mechanisms by which organisms can slow such accumulation, as well as how these mechanisms may themselves eventually break down and fail, is crucial to an understanding of the aging process. Repair pathways for damaged DNA have been well established (4); damaged proteins can be removed by a combination of proteolytic and repair pathways (3,(5)(6)(7)(8). However, we only are beginning to understand how cells can prevent the accumulation of damaged small molecules.To date, there are only a few pathways known for metabolizing damaged or unwanted small molecules. trans-Aconitate, the spontaneous degradation product of the citric acid cycle intermediate cis-aconitate, can be detoxified by the action of a specific methyltransferase (9). L-2-Hydroxyglutarate is formed as an abnormal byproduct when L-malate dehydrogenase uses ␣-ketoglutarate rather than oxalacetate as a substrate. The accumulation of the toxic L-2-hydroxyglutarate product is prevented, however, by the action of an enzyme that converts it back to ␣-ketoglutarate.

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Characterization of soybean tissue culture cell lines resistant to methionine analogs

Madison

Thompson

1988

Plant Cell Reports

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Several hundred soybean [Glycine max (L.) Merr.] cell lines resistant to ethionine were isolated either with or without chemical mutagenesis. of these, 26 were found to contain 2 to 22 times higher than normal levels of uncombined methionine. These 26 cell lines also contained higher than normal levels of S-adenosylmethionine and S-methylmethionine, but the levels of free lysine, threonine, cysteine, valine, tyrosine and phenylalanine were not elevated. Isoleucine levels were only slightly elevated. These results suggest that the regulation of methionine synthesis in vivo is more likely to be later in the pathway (after homoserine phosphate) than early in the pathway.

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Soybeans and radish leaves contain only one of the sulfonium diastereoisomers of S-adenosylmethionine

Cited by 15 publications

References 12 publications

S-Adenosylmethionine-Dependent Inactivation and Radiolabeling of 1-Aminocyclopropane-1-Carboxylate Synthase Isolated from Tomato Fruits

S-Adenosylmethionine-Dependent Inactivation and Radiolabeling of 1-Aminocyclopropane-1-Carboxylate Synthase Isolated from Tomato Fruits

Homocysteine Methyltransferases Mht1 and Sam4 Prevent the Accumulation of Age-damaged (R,S)-AdoMet in the Yeast Saccharomyces cerevisiae

Characterization of soybean tissue culture cell lines resistant to methionine analogs

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