Selenium: the pathway in the body

This page shows the biochemical pathway behind the laboratory value Selenium: which stations follow one another, which enzymes carry out each step and which cofactors they use. Every statement has a source. The page describes general textbook knowledge and says nothing about any individual person.

In brief

Selenium is a trace element that the body incorporates into proteins as selenocysteine. These selenoproteins convert peroxides to water and switch thyroid hormones into their active or inactive form.

The pathway step by step

1. Selenium in food → Selenide Selenocysteine lyase · Vitamin B6 (PLP) Selenocysteine lyase releases the selenium from the amino acid. Selenide is the common hub that feeds all further steps. Source 1, 2
2. Selenide → Selenophosphate SEPHS2 · ATP Selenophosphate synthetase 2 attaches selenide to a phosphate from ATP. Only in this form can selenium be built into proteins. Source 2
3. Selenophosphate → Selenocysteine on tRNA SEPSECS · Serine on tRNA, PSTK Serine is first bound to a dedicated transfer RNA, phosphorylated and then converted into selenocysteine with selenophosphate by the enzyme SEPSECS. Source 2
4. Selenocysteine on tRNA → Selenoprotein P Insertion at UGA codon · SECIS element When reading the genetic code, the cell inserts selenocysteine at the UGA codon; a signal in the RNA (SECIS element) makes this possible. The liver releases selenoprotein P into the blood; it carries selenium to the tissues. Source 3, 1
5. Selenium in the cell → Glutathione peroxidases This enzyme family carries selenocysteine in its active centre. It converts hydrogen peroxide and other peroxides into water. Source 4, 2
6. Selenium in the cell → Deiodinases The deiodinases also carry selenocysteine. They remove single iodine atoms from thyroid hormones and so determine which form is present in the tissue. Source 5
7. Hydrogen peroxide → Water Glutathione peroxidase · Glutathione (GSH) Glutathione peroxidase transfers electrons from glutathione to the peroxide; water and oxidised glutathione remain. Source 4
8. Thyroxine (T4) → Triiodothyronine (T3) Deiodinase Deiodinases remove one iodine atom, forming T3, which binds to receptor sites in the cell nucleus. Other deiodinases convert the hormones into inactive forms. Source 5

Cofactors in this pathway

• Glutathione — Supplies glutathione peroxidase with the electrons it uses to convert peroxides to water Source 4In the ORY catalogue as a laboratory value: Glutathion (GSH)
• Iodine — The selenium-containing deiodinases remove iodine atoms from T4 and T3 Source 5In the ORY catalogue as a laboratory value: Jod (Urin)
• Serine — Converted into selenocysteine on its own tRNA Source 2In the ORY catalogue as a laboratory value: Serin
• Vitamin B6 (PLP) — Cofactor of selenocysteine lyase, which releases selenium as selenide Source 1, 2In the ORY catalogue as a laboratory value: Vitamin B6
• ATP — Provides the phosphate with which SEPHS2 activates selenide to selenophosphate Source 2
• NADPH — Electron donor for the thioredoxin reductases, which are themselves selenoproteins Source 2

Sources

1. Burk RF, Hill KE. Regulation of Selenium Metabolism and Transport. Annu Rev Nutr 2015 · PubMed 25974694
2. Labunskyy VM, Hatfield DL, Gladyshev VN. Selenoproteins: molecular pathways and physiological roles. Physiol Rev 2014 · PubMed 24987004
3. Schomburg L. Selenoprotein P - Selenium transport protein, enzyme and biomarker of selenium status. Free Radic Biol Med 2022 · PubMed 36067902
4. Brigelius-Flohé R, Maiorino M. Glutathione peroxidases. Biochim Biophys Acta 2013 · PubMed 23201771
5. Köhrle J. Deiodinases control local cellular and systemic thyroid hormone availability. Free Radic Biol Med 2022 · PubMed 36206932

Related pathways

• 8-OHdG — hydrogen peroxide
• Glutathione — hydrogen peroxide
• Folic acid — Serin, Vitamin B6
• Methylation: methionine and homocysteine — Serin, Vitamin B6

As of 2026-09-16. Draft written by Claude to schema v2; sources checked in PubMed; expert review pending
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