Selenium Selenoproteins: Deiodinases, GPx and Thioredoxin Reductase

Selenium's value comes from its incorporation into selenocysteine, an amino acid placed at the active sites of specialized proteins. Human biology uses 25 selenoproteins, including deiodinases, glutathione peroxidases and thioredoxin reductases.

How do deiodinases use selenium?

Deiodinase enzymes remove iodine atoms from thyroid hormones, helping activate T4 into T3 or route hormone molecules toward inactive metabolites.

D1, D2 and D3 have distinct patterns

The three deiodinase families differ by tissue location, cellular compartment and preferred reaction, allowing local control rather than one uniform conversion rate.

Selenocysteine sits in the catalytic center

Its selenium atom has chemical properties that support efficient reduction reactions as the enzyme breaks a carbon-iodine bond.

What do glutathione peroxidases do?

Glutathione peroxidases use reduced glutathione to reduce hydrogen peroxide or lipid peroxides and then pass oxidized glutathione into a recycling pathway.

Peroxide control matters during thyroid synthesis

Thyroid peroxidase needs hydrogen peroxide for iodination, yet excess peroxide can modify cellular components. Local antioxidant enzymes help keep the chemistry organized.

Glutathione reductase completes the cycle

NADPH supplies electrons that regenerate reduced glutathione, connecting selenium enzymes with glucose metabolism and the cellular antioxidant network.

Why are thioredoxin reductases important?

Thioredoxin reductases use NADPH to restore reduced thioredoxin, which supports protein redox control, DNA synthesis and redox-sensitive signaling.

The thioredoxin system repairs reversible oxidation

Reduced thioredoxin donates electrons to oxidized protein groups and then returns to its active state through selenium-dependent thioredoxin reductase.

One mineral connects several formula pathways

In Thyroid Support Drops, selenium complements iodine as hormone starting material, zinc as an enzyme cofactor and L-tyrosine as an amino-acid building block.

Explore the connected wellness cluster

• Explore Thyroid Support Drops
• Follow iodide transport and organification
• Compare zinc homeostasis pathways
• Explore the antioxidant defense network
• Browse Energy & Metabolism

Frequently asked questions

What is a selenoprotein?

It is a protein that contains the amino acid selenocysteine. Selenocysteine often appears directly in the enzyme's active site.

Which enzymes convert thyroid hormones?

D1, D2 and D3 deiodinases control iodine removal. Their tissue-specific patterns shape local thyroid-hormone activity.

How does GPx use glutathione?

It transfers reducing power from glutathione to peroxides. Oxidized glutathione is then recycled using NADPH.

Is thioredoxin reductase selenium-dependent?

Mammalian thioredoxin reductases are selenoproteins. They keep thioredoxin available for redox reactions.

Research sources

• NIH ODS: Selenium and selenoprotein functions
• Selenoprotein enzyme-system research