Conjugation of reduced glutathione to a wide number of exogenous and endogenous hydrophobic electrophiles. glutathione + RX = a halide anion + an S-substituted glutathione + H(+) Homodimer. Yb subclass selectively binds steroid hormones. Belongs to the GST superfamily. Mu family. Gstm7 is the putative ortholog of human GSTM2.