Microsomal glutathione transferase 1, MGST1, belongs to a recently characterised superfamily named MAPEG (membrane associated proteins in eicosanoid and glutathione metabolism) which has evolved divergent functions to protect against reactive lipid intermediates (lipid hydroperoxides and hydroxyalkenals) or indeed harness these molecules for key physiological functions (leukotrienes and prostaglandins). The most thoroughly studied member of this superfamily is MGST1 which is an abundant detoxication enzyme displaying both glutathione transferase and peroxidase activities.
The MGST1 monomer has a molecular mass of 17.5 kD and three to four transmembrane regions can be localized from hydropathy plots (Fig. 1). One transmembrane stretch was shown by trypsin cleavage to be situated between lysine-4 and lysine-41 with the N-terminal on the lumenal side of the membrane. The active site is located on the cytoplasmic side of the endoplasmic reticulum.