Glutathione Reductase (GR) is a homodimeric flavoprotein disulfide oxidoreductase that plays a critical role in the prevention of oxidative damage within the cell. Glutathione Reductase helps to maintain appropriate levels of intracellular reduced glutathione (GSH) which is essential for maintaining the normal structure of red blood cells and for keeping hemoglobin in the ferrous state. Glutathione Reductase together with its co-factor, NADPH, catalyzes the reduction of oxidized glutathione (glutathione disulfide, GSSG) to glutathione. GSH is also a reactant for Glutathione Peroxidase, which converts hydrogen peroxide hydrogen peroxide (H2O2) into water. Glutathione Reductase is expressed as both mitochondrial and cytosolic isoforms, as determined by the presence or absence of an N-terminal transit peptide.