Exhibits glutathione-dependent thiol transferase and dehydroascorbate reductase activities. Has S-(phenacyl)glutathione reductase activity. Has also glutathione S-transferase activity. Participates in the biotransformation of inorganic arsenic and reduces monomethylarsonic acid (MMA) and dimethylarsonic acid. 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 Homodimer. Most abundant in the liver and skeletal muscle; also expressed in heart, diaphragm, colon, thymus, kidney, lung, ovaries, spleen, intestine and pancreas. Belongs to the GST superfamily. Omega family.