The glutathione peroxidase family of enzymes (abbreviated GSH-Px) catalyze reduction of hydrogen peroxide and organic hydroperoxides:
:2GSH + HO   →   GSSG  +  2 HO
The two H atoms are donated by thiols in a process that begins with oxidation of a selenol side chain in GSH-Px.  The organoselenium compound ebselen is a drug used to supplement the action of GSH-Px.  It functions as a catalyst for the destruction of hydrogen peroxide.
A related selenium-containing enzyme in some plants and in animals (thioredoxin reductase) generates reduced thioredoxin, a dithiol that serves as an electron source for peroxidases and also the important reducing enzyme ribonucleotide reductase that makes DNA precursors from RNA precursors.