Conjugation of reduced glutathione to a wide number of exogenous and endogenous hydrophobic electrophiles. glutathione + RX = a halide anion + an S-substituted glutathione + H(+) Can be activated by reagents that attack Cys-50 sulfhydryl, such as N-ethylmaleimide. Activation also occurs via nitration of Tyr-93 by peroxynitrite (By similarity). Homotrimer; The trimer binds only one molecule of glutathione. Peroxynitrite induces nitration at Tyr-93 which activates the enzyme. Belongs to the MAPEG family.