Exhibits glutathione-dependent thiol transferase activity. Has high dehydroascorbate reductase activity and may contribute to the recycling of ascorbic acid. Participates in the biotransformation of inorganic arsenic and reduces monomethylarsonic acid (MMA). glutathione + RX = a halide anion + an S-substituted glutathione + H(+) 2 glutathione + L-dehydroascorbate = glutathione disulfide + L-ascorbate 2 glutathione + H(+) + methylarsonate = glutathione disulfide + H2O + methylarsonous acid Belongs to the GST superfamily. Omega family.