Table 3.

Main groups of selenoproteins found in the thyroid gland and their function [1, 2].

Glutathione peroxidase	GPX	Catalyzes the reduction of H2O2 and protects against oxidative stress
Cytosolic GPx 1	GPX1	Antioxidative defense
Gastrointestinal GPx 2	GPX2	Antiapoptotic function in colon crypts; helps to maintain intestinal mucosal integrity
Extracellular GPx 3	GPX3	Antioxidant in extracellular fluid; thyroid protection from hydrogen peroxide in thyrocytes and follicular lumen
Phospholipid GPx 4	GPX4	Reduces the phospholipids' hydroperoxides; regulates apoptosis
Iodothyronine deiodinase	DIO	Production of active thyroid hormone T3, reverse T3 (rT3), and T2
Type I DIO	DIO1	Conversion of T4 to T3
Type II DIO	DIO2	Local production (intracellular) of T3 from T4
Type III DIO	DIO3	Production of rT3 from T4 and T2 from T3
Thioredoxin reductase	TXNRD	Oxidoreductase activity having NADPH as a cofactor
TXNRD cytosolic	TXNRD1	Main antioxidant at the cellular level
TXNRD mitochondrial	TXNRD2	Regulates cell proliferation