Glutathione S-transferase that catalyzes the nucleophilic attack of the sulfur atom of glutathione on the electrophilic groups of a wide range of exogenous and endogenous compounds (Probable). Involved in the formation of glutathione conjugates of both prostaglandin A2 (PGA2) and prostaglandin J2 (PGJ2) (PubMed:9084911). It also catalyzes the isomerization of D5-androstene-3,17-dione (AD) into D4-androstene-3,17-dione and may therefore play an important role in hormone biosynthesis (PubMed:11152686). Through its glutathione-dependent peroxidase activity toward the fatty acid hydroperoxide (13S)-hydroperoxy-(9Z,11E)-octadecadienoate/13-HPODE it is also involved in the metabolism of oxidized linoleic acid (PubMed:16624487). glutathione + RX = a halide anion + an S-substituted glutathione + H(+) glutathione + prostaglandin A2 = prostaglandin A2-S-(R)-glutathione glutathione + prostaglandin J2 = prostaglandin J2-S-(R)-glutathione (13S)-hydroperoxy-(9Z,11E)-octadecadienoate + 2 glutathione = (13S)-hydroxy-(9Z,11E)-octadecadienoate + glutathione disulfide + H2O androst-5-ene-3,17-dione = androst-4-ene-3,17-dione The isomerase activity is inhibited by S-methylglutathione (GSMe). kcat is 29.3 sec(-1) for the isomerization of androst-5-ene-3,17-dione. Optimum pH is 8.0 for the isomerization of androst-5-ene-3,17-dione. Homodimer or heterodimer of GSTA1 and GSTA2. Liver. The C-terminal domain may form a component of the hydrophobic substrate-binding site, but in contrast appears not to be directly involved in GSH binding and is not absolutely essential for catalytic activity. Belongs to the GST superfamily. Alpha family.