First, γ-glutamyl cysteine is synthesized from l-glutamate and cysteine using GCL. Then, GSS catalyses the condensation of γ-glutamyl cysteine and glycine to form GSH. GSH is used as a cofactor by GPx to reduce H2O2, resulting in the formation of GSSG. GR reduces GSSG to two GSH by NADPH (Abbreviation: GST, glutathione S-transferase).