Glutathione reductase (GR) is a member of pyridine nucleotide- disulfideoxidoreductases, which includes the closely related enzymes thioredoxin reductase, lipoamide dehydrogenase, trypanothione reductase and mercuric ion reductase. GR is a cytoplasmic flavoenzyme widely distributed in aerobic organisms. The dimeric protein is composed of two identical subunits, each containing 1 FAD and 1 redox-active disulfide/dithiol as components of the catalytic apparatus. It plays a role in maintaining glutathione (GSH) in its reduced form by catalyzing the reduction of glutathione disulfide (GSSG): GSSG + NADPH + H+?2GSH + NADP+. In mosteukaryotic cells, GR maintains the ratio of [GSH]/[GSSG], and participates in several vital functions such as the detoxification of reactive oxygen species as well as protein and DNA biosynthesis.