Glutathione helps protect cells from free radical damage by acting as an antioxidant. Within cells, glutathione exists in reduced (GSH) and oxidized (GSSG) states. In healthy cells and tissue, more than 90% of the pool is in the reduced form (GSH) while less than 10% exists in the disulfide form (GSSG). The GSH form acts as an electron donor and is thereby oxidized itself to the GSSG form.
Glutathione reductase is a homodimeric enzyme that is a member of the flavoprotein disulfide oxidoreductases. Glutathione Reductase reduces oxidized glutathione (GSSG) back to reduced glutathione (GSH) in the presence of NADPH.