Selenomethionine (SeMet) is a naturally occurring

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...

. The L-selenomethionine

enantiomer In chemistry, an enantiomer ( /ɪˈnænti.əmər, ɛ-, -oʊ-/ ''ih-NAN-tee-ə-mər''; from Ancient Greek ἐνάντιος ''(enántios)'' 'opposite', and μέρος ''(méros)'' 'part') – also called optical isomer, antipode, or optical ant ...

is the main form of

selenium Selenium is a chemical element with the symbol Se and atomic number 34. It is a nonmetal (more rarely considered a metalloid) with properties that are intermediate between the elements above and below in the periodic table, sulfur and tellurium, ...

found in

Brazil nuts The Brazil nut (''Bertholletia excelsa'') is a South American tree in the family Lecythidaceae, and it is also the name of the tree's commercially harvested edible seeds. It is one of the largest and longest-lived trees in the Amazon rainforest. ...

, cereal grains,

soybeans The soybean, soy bean, or soya bean (''Glycine max'') is a species of legume native to East Asia, widely grown for its edible bean, which has numerous uses. Traditional unfermented food uses of soybeans include soy milk, from which tofu and ...

, and grassland

legumes A legume () is a plant in the family Fabaceae (or Leguminosae), or the fruit or seed of such a plant. When used as a dry grain, the seed is also called a pulse. Legumes are grown agriculturally, primarily for human consumption, for livestock fo ...

, while ''Se''-methylselenocysteine, or its γ-glutamyl derivative, is the major form of selenium found in ''

Astragalus ''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 largest genus of plants in terms of described species. The genus is native to tempe ...

'', ''

Allium ''Allium'' is a genus of monocotyledonous flowering plants that includes hundreds of species, including the cultivated onion, garlic, scallion, shallot, leek, and chives. The generic name ''Allium'' is the Latin word for garlic,Gledhill, Davi ...

'', and ''

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, or mustard plants. Crops from this genus are sometimes called ''cole cr ...

'' species. ''In vivo'', selenomethionine is randomly incorporated instead of

methionine Methionine (symbol Met or M) () is an essential amino acid in humans. As the precursor of other amino acids such as cysteine and taurine, versatile compounds such as SAM-e, and the important antioxidant glutathione, methionine plays a critical ro ...

. Selenomethionine is readily oxidized. Selenomethionine's antioxidant activity arises from its ability to deplete

reactive oxygen species In chemistry, reactive oxygen species (ROS) are highly reactive chemicals formed from diatomic oxygen (). Examples of ROS include peroxides, superoxide, hydroxyl radical, singlet oxygen, and alpha-oxygen. The reduction of molecular oxygen () p ...

Selenium Selenium is a chemical element with the symbol Se and atomic number 34. It is a nonmetal (more rarely considered a metalloid) with properties that are intermediate between the elements above and below in the periodic table, sulfur and tellurium, ...

and

also play separate roles in the formation and recycling of

glutathione Glutathione (GSH, ) is an antioxidant in plants, animals, fungi, and some bacteria and archaea. Glutathione is capable of preventing damage to important cellular components caused by sources such as reactive oxygen species, free radicals, pero ...

, a key endogenous antioxidant in many organisms, including humans.

Substitution chemistry issues

Selenium and sulfur are

chalcogen The chalcogens (ore forming) ( ) are the chemical elements in group 16 of the periodic table. This group is also known as the oxygen family. Group 16 consists of the elements oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and the radioact ...

s that share many chemical properties so the substitution of methionine with selenomethionine may have only a limited effect on protein structure and function. However, the incorporation of selenomethionine into tissue proteins and keratin in the cattle, birds and fish causes alkali disease. Alkali disease is characterized by emaciation, loss of hair, deformation and shedding of hooves, loss of vitality, and erosion of the joints of long bones. Incorporation of selenomethionine into proteins in place of

aids the structure elucidation of proteins by

X-ray crystallography X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...

using single- or

multi-wavelength anomalous diffraction Multi-wavelength anomalous diffraction (sometimes Multi-wavelength anomalous dispersion; abbreviated MAD) is a technique used in X-ray crystallography that facilitates the determination of the three-dimensional structure of biological macromolecules ...

(SAD or MAD). The incorporation of heavy atoms such as selenium helps solve the

phase problem In physics, the phase problem is the problem of loss of information concerning the phase that can occur when making a physical measurement. The name comes from the field of X-ray crystallography, where the phase problem has to be solved for the det ...

in X-ray crystallography.

Dietary intake

Selenomethionine is readily available as a dietary supplement. It has been suggested by nutritionists that selenomethionine, as an organic form of selenium, is easier for the human body to absorb 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 ...

, which is an inorganic form. It was determined in a clinical trial that selenomethionine is absorbed 19% better than selenite.

References

External links

PDB file for MSE
{{Webarchive, url=https://web.archive.org/web/20180920083516/http://xray.bmc.uu.se/hicup/MSE/ , date=2018-09-20

Amino acids Organoselenium compounds Selenium(−II) compounds Selenoethers

Substitution chemistry issues

Dietary intake

See also

References

External links