Fig. 1

Glutathione biosynthesis in yeast is a two-step process catalysed by Gsh1 and Gsh2 involving three amino acids: cysteine, glutamate, glycine, and two molecules of ATP. In some bacteria, the bioconversion is carried out in a single-step pathway by a bifunctional enzyme GshF that is free from feedback inhibition of the product, unlike in yeast where GSH inhibits the activity of Gsh1. During deactivation of reactive oxygen species (ROS), GSH is oxidised to GSSG. Oxidised GSSG is reduced back to GSH by glutathione reductase (Glr1) using NADPH as a co-factor. In actively growing cells, the pentose phosphate pathway (PPP) supplies the NADPH