Conjugation of reduced glutathione to a wide number of exogenous and endogenous hydrophobic electrophiles. Catalyzes isomerization reactions that contribute to the biosynthesis of steroid hormones. Efficiently catalyze obligatory double-bond isomerizations of delta(5)-androstene-3,17-dione and delta(5)-pregnene-3,20-dione, precursors to testosterone and progesterone, respectively. Has substantial activity toward aflatoxin B1-8,9-epoxide (By similarity). glutathione + RX = a halide anion + an S-substituted glutathione + H(+) androst-5-ene-3,17-dione = androst-4-ene-3,17-dione pregn-5-ene-3,20-dione = progesterone kcats are 102 sec(-1) and 27 sec(-1) for androst-5-ene-3,17-dione and pregn-5-ene-3,20-dione as substrates, respectively (at pH 8.0 and 30 degrees Celsius). Homodimer. Belongs to the GST superfamily. Alpha family. Extended N-terminus. Extended N-terminus.