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, except in the testis. Activation also occurs via nitration of Tyr-93 by peroxynitrite. Homotrimer; The trimer binds only one molecule of glutathione. Highest in the liver, followed by kidney and testis and much lower in seminal vesicles, spleen, lung and brain. Peroxynitrite induces nitration at Tyr-93 which activates the enzyme. Belongs to the MAPEG family.