Selenium and selenocysteine
: Roles in cancer, health, and development.
Selenium is a trace element that functions within selenocysteine
, an amino acid that makes up part of a category of proteins called selenoproteins.
It is found in body tissue principally as selenomethionine (SeMet) or as selenocysteine
(SeCys), the latter found in selenium, glutathione peroxidase (GSHPx).
, pyrrolysine, and the unique energy metabolism of methanogenic archaea.
(177), acetylphenylalanine (178), and para-azidomethyl-1- phenylalanine (42).
The major biological form of Se is selenocysteine
, the 21st proteinogenic amino acid, which is related to its presence in the active center of selenoenzymes (especially GPx as the main enzymatic system which participates in the defense against free radicals Hg-induced and TrxR, which coordinates Hg-induced redox reactions maintaining the proper cellular function) and Se-dependent proteins like selenoprotein P (SeP), the best known selenoprotein in plasma, which protects organism against Hg toxicity.
It is also an essential component in the selenoproteins, including selenophosphate and selenocysteine
, with vitamin [B.sub.6] as the catalyst.
residue replaced by cysteine in thioredoxin reductase from selenium-deficient rat liver.
After saturation, selenomethionine can interfere in the serum levels of selenium, as a result of its non-regulated incorporation in methionine-containing proteins, while sodium selenite will no longer be used efficiently for biosynthesis of selenocysteine
. (28) The bioavailability of sodium selenite represents two thirds of the absorption of selenomethionine, thus suggesting greater effectiveness of selenomethionine supplementation when compared with sodium selenite.
Berry, "Regulation of human thioredoxin reductase expression and activity by 3-untranslated region selenocysteine
insertion sequence and mRNA instability elements," Journal of Biological Chemistry, vol.
Glyphosate, which is widely used as an herbicide in the main soybean and corn-producing area surrounding the city of Buenos Aires, has been linked to disorders of selenium metabolism and could disrupt the synthesis of selenocysteine
, which is a fundamental component of enzymes that protect the thyroid follicular cells from free radicals [37, 39].
The genetic defects affect different proteins with essential roles in muscle development and function: defects of structural proteins (laminin-[alpha]2, collagen, integrin, and plectin), defects of glycosylation (Walker-Warburg syndrome, muscle-eye brain disease, and Fukuyama CMD), proteins of the endoplasmic reticulum and nucleus (selenoprotein, selenocysteine
insertion sequence-binding protein 2, laminin A/C), and mitochondrial membrane protein (choline kinase beta).