Fig 1.

Glutathione and thioredoxin antioxidant defense systems. (A) Reduced glutathione functions in quenching radicals, maintaining thiol groups, serving as a co-enzyme for glutathione peroxidase and maintaining cellular redox homeostasis. GPx reduces H₂O₂ to H₂O while oxidizing GSH to GSSG. GSR then uses NADPH as a co-factor to form -SH groups in proteins that interact with the reduction of GSSG to GSH. (B) Thioredoxin reduces H₂O₂ and protein disulfide, in protein repair and DNA synthesis, regulating transcription factors and apoptosis, and in immunomodulation. PRX reduces H₂O₂ to H₂O while oxidizing reduced thiore-doxin. NADPH-dependent TXNRD then catalyzes the reduction of oxidized thioredoxin. GPx=glutathione peroxidase, GSH = reduced glutathione, GSSG = oxidized glutathione, GSR = glutathione reductase, NADP = reduced nicotinamide adenine dinucleotide phosphate, PRX = peroxiredoxin, TXNRD = thioredoxin reductase