Figure 2: Glutathione redox cycle. Glutathione (GSH) is synthesized from the amino acids glutamate (Glu), cysteine (Cys), and glycine (Gly) in a two-step pathway requiring energy from ATP. Glu and Cys are combined via the action of glutamate cysteine ligase (GCL). This dipeptide then combines with Gly via a reaction from glutathione synthetase (GS). GSH undergoes a redox reaction using glutathione peroxidase GPx to detoxify reactive oxygen species (ROS) like hydrogen peroxide (). The main source of is from the conversion of superoxide anion () by the enzymatic action of superoxide dismutase (SOD). GSH is converted to an oxidized form (GSSG) and is recycled back to GSH by the enzymatic reaction of glutathione reductase (GR) which requires the cofactor nicotinamide adenine dinucleotide phosphate (NADPH) to form a redox cycle. NB: bold and underlined text represents enzymes.