Glutathione

A tripeptide (gamma-L-glutamyl-L-cysteinyl-glycine, CAS 70-18-8), the major intracellular antioxidant and the primary substrate of glutathione-S-transferases and glutathione peroxidases. Oral bioavailability is poor due to gastrointestinal hydrolysis — hence the injectable, liposomal, and topical formulations offered by research-peptide vendors. Studied for roles in hepatoprotection, oxidative-stress modulation, and skin depigmentation. Not a peptide in the signaling sense but catalogued here for commercial-intent reasons alongside the longevity cofactors.