The protein encoded by this gene is a member of the glutathione peroxidase family, which reduces organic hydroperoxides and hydrogen peroxide (H2O2) using glutathione, protecting cells from oxidative damage. This isozyme is mainly expressed in the gastrointestinal tract and liver (in humans), localized in the cytoplasm, and prefers hydrogen peroxide as its substrate. Overexpression is linked to increased differentiation and proliferation in colorectal cancer. It is also a selenoprotein, with selenocysteine (Sec) at its active site, encoded by the UGA codon. The 3 UTR of selenoprotein mRNAs contains a stem-loop structure called the SECIS element, essential for interpreting UGA as Sec, not a stop codon. Alternative splicing variants of this gene have been identified.