Definition
ChEBI: Selenomethionine is a selenoamino acid that is the selenium analogue of methionine. It has a role as a plant metabolite. It is a member of selenomethionines and a selenoamino acid.
Biological Functions
Most selenium in animal tissues is present as selenomethionine or selenocysteine. Selenomethionine, which cannot be synthesized by humans and is initially synthesized in plants, is incorporated randomly in place of methionine in a variety of proteins obtained from plant and animal sources. Selenium is present in varying amounts in these proteins, which are called selenium-containing proteins.
Selenomethionine is not known to have a physiological function separate from that of methionine.
Selenocysteine is present in animal selenoproteins that have been characterized (see below) and is the form of selenium that accounts for the biological activity of the element. In contrast to selenomethionine, there is no evidence that selenocysteine substitutes for cysteine in humans.
General Description
This certified reference material (CRM) is produced and certified in accordance with ISO/IEC 17025 and ISO 17034. This CRM is traceable to primary material from an NMI, e.g. NIST or NMIJ.
Certified content by quantitative NMR incl. uncertainty and expiry date are given on the certificate.
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Biological Activity
Most dietary selenium is highly bioavailable. Selenomethionine, which is estimated to account for at least half of the dietary selenium, is absorbed by the same mechanism as methionine, and its selenium is made available for selenoprotein synthesis when it is catabolized via the transsulfuration pathway (Esaki et al., 1982). The bioavailability of selenium in the form of selenomethionine is greater than 90 percent (Thomson and Robinson, 1986). The selenium in selenocysteine, another significant dietary form, is also highly bioavailable (Swanson et al., 1991). There appear to be some minor dietary forms of selenium (especially present in fish) that have relatively low bioavailability, but these forms have not been identified (Cantor and Tarino, 1982). Selenate and selenite, two inorganic forms of selenium, have roughly equivalent bioavailability which generally exceeds 50 percent (Thomson and Robinson, 1986). Although they are not major dietary constituents, these inorganic forms are commonly used as selenium supplements.
Metabolism
Selenomethionine, derived mainly from plants, enters the methionine pool in the body and shares the fate of methionine until catabolized by the transsulfuration pathway. The resulting free selenocysteine is further broken down with liberation of a reduced form of the element, which is designated selenide (Esaki et al., 1982). Ingested selenite, selenate, and selenocysteine are all apparently metabolized directly to selenide. This selenide may be associated with a protein that serves as a chaperone (Lacourciere and Stadtman, 1998). The selenide can be metabolized to selenophosphate, the precursor of selenocysteine in selenoproteins (Ehrenreich et al., 1992) and of selenium in transfer RNA (Veres et al., 1992), or it can be converted to excretory metabolites (Mozier et al., 1988), some of which have been characterized as methylated forms.
Purification Methods
It crystallises in hexagonal plates from MeOH and H2O. [Klosterman & Painter J Am Chem Soc 69 2009 1949.] The L-isomer [3211-76-5] is purified by dissolving it in H2O, adjusting the pH to 5.5 with aqueous NH3, evaporating to near-dryness, and the residue is washed several times with absolute EtOH till a solid is formed and then recrystallise from Me2CO. It has m 266-268o(dec) [also 275o(dec)], and [] D +18.1o(c 1, N HCl). [Pande et al. J Org Chem 35 1440 1970, Beilstein 4 IV 3216.]
