Fig. 1.

GSH biosynthetic route and GSH cycle. GSH biosynthesis occurs in two different and ATP-dependen steps. The first and limiting step is carried out by GCL, formed by two subunits GCLc and GCLm. In this step l-Glu and l-Cys react to form γ-glutamyl-cisteine. GS is responsible of the second step, that joins l-Gly forming γ-glutamyl-cisteinyl-glicine (GSH). As well as aerobic respiration or other ROS sources increase H₂O₂, that should be metabolized, in this case GPx generating GSSG. This GSSG could be reduced to GSH again with the help of GR GR, creating a redox cycle, using as reducing agent NAPDH, from Penthoses Phosphate Pathway (PPP).