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 (By similarity). Has a high catalytic activity for aflatoxin B1-8,9 epoxide (PubMed:1637297). 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 Homodimer. Belongs to the GST superfamily. Alpha family.