Methylselenocysteine (Me-Sec), also known as ''Se''-methylselenocysteine (SeMSC), is an

analog Analog or analogue may refer to: Computing and electronics * Analog signal, in which information is encoded in a continuous variable ** Analog device, an apparatus that operates on analog signals *** Analog electronics, circuits which use analog ...

of ''S''-methylcysteine in which the sulfur atom is replaced with a selenium atom.

Occurrence

Methylselenocysteine is found in many vegetables: "as much as 80% of the total selenium" found in ''

Allium ''Allium'' is a large genus of monocotyledonous flowering plants with around 1000 accepted species, making ''Allium'' the largest genus in the family Amaryllidaceae and among the largest plant genera in the world. Many of the species are edible, ...

'' species (

onion An onion (''Allium cepa'' , from Latin ), also known as the bulb onion or common onion, is a vegetable that is the most widely cultivated species of the genus '' Allium''. The shallot is a botanical variety of the onion which was classifie ...

leek A leek is a vegetable, a cultivar of ''Allium ampeloprasum'', the broadleaf wild leek (synonym (taxonomy), syn. ''Allium porrum''). The edible part of the plant is a bundle of Leaf sheath, leaf sheaths that is sometimes erroneously called a "s ...

garlic Garlic (''Allium sativum'') is a species of bulbous flowering plants in the genus '' Allium''. Its close relatives include the onion, shallot, leek, chives, Welsh onion, and Chinese onion. Garlic is native to central and south Asia, str ...

ramps A ramp, or inclined plane, is a simple machine. Ramp, Ramps, RAMP, may also refer to: People * James J. Ramp (died 1978), Philadelphia police officer * Jenny Ramp (born 2003), Filipina beauty pageant titleholder * Pieter Ramp (1592–1660), ...

) ''

Brassica ''Brassica'' () is a genus of plants in the cabbage and mustard family (Brassicaceae). The members of the genus are informally known as cruciferous vegetables, cabbages, mustard plants, or simply brassicas. Crops from this genus are sometim ...

'' species (

broccoli Broccoli (''Brassica oleracea'' var. ''italica'') is an edible green plant in the Brassicaceae, cabbage family (family Brassicaceae, genus ''Brassica'') whose large Pseudanthium, flowering head, plant stem, stalk and small associated leafy gre ...

radish The radish (''Raphanus sativus'') is a flowering plant in the mustard family, Brassicaceae. Its large taproot is commonly used as a root vegetable, although the entire plant is edible and its leaves are sometimes used as a leaf vegetable. Origina ...

Brussels sprouts The Brussels sprout is a member of the Gemmifera cultivar group of cabbages (''Brassica oleracea''), grown for its edible buds. Etymology Though native to the Mediterranean region with other cabbage species, Brussels sprouts first appeared i ...

cabbage Cabbage, comprising several cultivars of '' Brassica oleracea'', is a leafy green, red (purple), or white (pale green) biennial plant grown as an annual vegetable crop for its dense-leaved heads. It is descended from the wild cabbage ( ''B.& ...

), and

milk vetch ''Astragalus'' is a large genus of over 3,000 species of herbs and small shrubs, belonging to the legume family Fabaceae and the subfamily Faboideae. It is the List of the largest genera of flowering plants, largest genus of plants in terms of d ...

(''

Astragalus Astragalus may refer to: * ''Astragalus'' (plant), a large genus of herbs and small shrubs *Astragalus (bone) The talus (; Latin for ankle or ankle bone; : tali), talus bone, astragalus (), or ankle bone is one of the group of foot bones known ...

'' species,

Fabaceae Fabaceae () or Leguminosae,International Code of Nomen ...

) is present as ''Se''-methylselenocysteine. It is also present in

selenized yeast Selenium yeast is ''Saccharomyces cerevisiae'' (baker's yeast) grown in a selenium-rich media. It contains selenium in the form of organic and inorganic compounds. It is used both as a feed additive for livestock and as a dietary supplement for h ...

(''

Saccharomyces cerevisiae ''Saccharomyces cerevisiae'' () (brewer's yeast or baker's yeast) is a species of yeast (single-celled fungal microorganisms). The species has been instrumental in winemaking, baking, and brewing since ancient times. It is believed to have be ...

'' grown in a high-selenium culture).

Biosynthesis

In plants it is produced by a dedicated selenocysteine methyltransferase. Adding inorganic selenium to the soil increases the expression of the gene in plants. In yeast it is also made by a selenomethyltransferase, though as no specific enzyme has been identified, it is possible that this happens via a promiscuous reaction of another enzyme.

Function

Me-Sec activates a number of transcriptional factors in plants, leading to higher production of secondary metabolites including

capsaicin Capsaicin (8-methyl-''N''-vanillyl-6-nonenamide) (, rarely ) is an active component of chili peppers, which are plants belonging to the genus ''Capsicum''. It is a potent Irritation, irritant for Mammal, mammals, including humans, and produces ...

in chili pepper; carotenoid, phenols, glucosinolates, and sulforaphane in ''Brassica''.

Dietary aspects

The bioavailability of selenium from ''Se''-methylselenocysteine, "is likely to be similar to that from other organic selenium compounds." Specifically, "it is converted via the action of β-lyase, to methylselenol and then to

hydrogen selenide Hydrogen selenide is an inorganic compound with the formula H2Se. This hydrogen chalcogenide is the simplest and most commonly encountered hydride of selenium. H2Se is a colorless, flammable gas under standard conditions. It is the most toxic se ...

," which is also the key metabolite derived from all other common forms of selenium. But EFSA concluded that "given the absence of human studies on ''Se''-methylselenocysteine, the relatively sparse database on the

bioavailability In pharmacology, bioavailability is a subcategory of absorption and is the fraction (%) of an administered drug that reaches the systemic circulation. By definition, when a medication is administered intravenously, its bioavailability is 100%. H ...

of selenium from this source and the limited data on the safety of this source compared with other selenium compounds, the Upper Limit for selenium defined by the

Scientific Committee on Food The Scientific Committee on Food (SCF), established in 1974, was the main committee providing the European Commission with scientific advice on food safety. "Scientific Committee on Food - FOOD STANDARDS AGENCY" (overview), Gov.uk, F ...

cannot be used for judging its safety."

Health claims

It is an inhibitor of DMBA-induced mammary tumors and a " chemopreventive agent that blocks

cell cycle The cell cycle, or cell-division cycle, is the sequential series of events that take place in a cell (biology), cell that causes it to divide into two daughter cells. These events include the growth of the cell, duplication of its DNA (DNA re ...

progression and proliferation of premalignant mammary lesions and induces

apoptosis Apoptosis (from ) is a form of programmed cell death that occurs in multicellular organisms and in some eukaryotic, single-celled microorganisms such as yeast. Biochemistry, Biochemical events lead to characteristic cell changes (Morphology (biol ...

of cancer cell lines in culture."

Apoptosis Apoptosis (from ) is a form of programmed cell death that occurs in multicellular organisms and in some eukaryotic, single-celled microorganisms such as yeast. Biochemistry, Biochemical events lead to characteristic cell changes (Morphology (biol ...

has been proposed as the most plausible mechanism for the chemopreventive activities of selenocompounds. ''Se''-Methylselenocysteine was more efficient at inducing apoptosis than

selenite Selenite may refer to: Substances containing selenium *A selenium-containing anion or ionic compound with the SeO32− anion: **Selenite (ion), anion is a selenium oxoanion with the chemical formula SeO32− ***Selenous acid, the conjugate acid, w ...

, but was less toxic. The "selenite-induced cell death could be derived from

necrosis Necrosis () is a form of cell injury which results in the premature death of cells in living tissue by autolysis. The term "necrosis" came about in the mid-19th century and is commonly attributed to German pathologist Rudolf Virchow, who i ...

rather than apoptosis, since selenite did not significantly induce several apoptotic phenomena, including the activation of

caspase-3 Caspase-3 is a caspase protein that interacts with caspase-8 and caspase-9. It is encoded by the ''CASP3'' gene. ''CASP3'' orthologs have been identified in numerous mammals for which complete genome data are available. Unique orthologs are also ...

." In the Nutritional Prevention of Cancer Trial,

resulted in "a reduction in the incidence of prostate cancer and in total cancer incidence"; subsequent anticancer studies using selenomethionine did not show any benefit against cancer; but, selenized yeast contains both selenomethionine and methylselenocysteine.

References

{{Reflist Amino acid derivatives Selenium(−II) compounds Selenoethers