Selenomethionine is a naturally occurring amino acid containing the essential trace mineral selenium.
This mineral is present in natural food sources as L-enantiomer of selenomethionine, which is commonly known as Sem and SE-met (selenium-methionine).
Molecular formula of selenomethionine is C5H11NO2Se.During the synthesis of the methionine, when available, it is incorporated randomly instead of sulfur and SeMet is formed.
Seleno-amino acid, selenomethionine, is the best among the selenium supplementsSelenium in the form L-selenomethionine is present as a natural component of foods like cereals, nuts, meat and seafood.
Most of the L-selenomethione is absorbed in the small intestine region of gastrointestinal tract.
This process, as in the case of methionine is carrier-mediated by Na+ ions.
The intestinal absorption process recognises SeMet as amino acid take it up in greater quantities.
Unlike the inorganic forms of selenium like, sodium hydrogen selenite, sodium selenate and sodium selenite, L-selenomethionine shows high bioavailability and absorption rate of selenium to the order of more than 90%.
Sodium selenate is well absorbed by the gastrointestinal tract, but most of it is excreted in urine without utilization.
As for sodium selenite up to 50% is absorbed; however it is retained better than selenate.
Organic acid forms like L-selenomethionine are well absorbed and well utilized by the body.
In adult human body pool 5-15 mg of selenium is present of which nearly 50% is present in skeletal muscle.
Once absorbed from L-SeMet it is incorporated for a long term in the body pool.
In the body SeMet half-life is 250 days where as inorganic sodium selenite half-life is only 100 days.
L-selenomethionine is found to be stable with a shelf life of more than three years.U.S. Food and Drug Administration (FDA) has approved L-SeMet for use in dietary supplements with various formulations.
Synthesis of selenium L-selenomethionineFor large scale synthetic production of SeMet, L-methionine is initially transformed to methyl-methionine derivative.
By hydrolysis methyl-methionine compound is converted to homoserine and then into α-amino-γ-butyrolactone.
This compound on reacting with HBr converts into 2-amino-4-bromobutanoic acid. Then it is reacted with LiSeCH3 to obtain L-selenomethionine.SeMet produced in such manner with high purity is marketed as yeast-free selenium and is preferred by some patients.
Biosynthesis of selenomethionineMost of the plants, when inorganic water soluble salts are available in soil, synthesize the selenium amino acid SeMet.
When spirulina is cultured in a medium high in inorganic salts, synthesises and accumulates SeMet in the cells. However this spirulina source is less effective in boosting the mineral levels in humans.
Enriched yeast is produced by growing yeast in medium rich in inorganic salts.Selenium yeast is the best source of this organic biosynthesized selenomethionine, as it can produced in great quantities and is less expensive.
Selenomethionine safetyThe synthetic product being very pure is listed as a very toxic substance in material Safety Data Sheets.
It should be handled with all the necessary care and its inhalation should be avoided.
However nutritional supplements of inorganic salts and organic forms like selenium yeast are only toxic when the upper tolerance levels are exceeded for a long period.
For more information on 'Upper tolerance level' of selenomethionine read topic on 'Selenium overdose and side effects'.
Selenomethionine - Selenium amino acid (current topic).