Biosynthetic pathway of GSH. APS1–4, ATP sulfurylases 1–4; APR1-4, adenosine phosphosulfate reductases 1–4; GSH1 & 2, GSH synthetase 1 & 2; OASTL, O-acetylserine (thiol) lyase; OPT6, oligopeptide transporter 6; SERAT, serine acetyl transferase; SIR, sulfite reductase.