Schematic representation of the γ-glutamyl cycle.

Gamma glutamyl transferase (GGT) metabolizes glutathione, in the presence of an amino acid, to form a γ-glutamyl amino acid and cysteinylglycine. γ-glutamyl amino acids are then metabolized to oxoproline and an amino acid and oxoproline is converted back to glutathione. Metabolites in red were significantly affected either by O₃ or antibiotics or both.