Glutathione S-transferases (GSTs) provide protection to cells against electrophilic xenobiotics as well as lipid hydroperoxides and 4-hydroxynonenal generated during lipid peroxidation. The catalytic properties of the alpha class GSTs are well suited for detoxification of electrophilic products of lipid peroxidation. An immunologically distinct subgroup of the alpha class GST isozymes having high activity towards 4-hydroxynonenal has been recently identified in several mammalian tissues [Zimniak et al. (1994) J. Biol. Chem. 269, 992-1000]. Since oxidative stress can exert deleterious effects during gestation, the present studies were performed to determine whether the rat homolog of this group of GSTs, rGST 8-8, is expressed in gravid rat uterus, where it may function as a defense mechanism against oxidative stress. GSTs were purified by GSH-affinity chromatography. Individual GST isozymes were separated by column isoelectric focusing and their immunologic identities were established using highly specific polyclonal antibodies in Western blot analysis. Their expression was quantified and kinetic properties were characterized. Rat uterus contained an alpha class GST (pI 9.8), a pi class GST (pI 8.1), two mu class GSTs (pI 6.7 and 6.2) and rGST 8-8. This result indicated that rGST subunits 1, 2, 3, 4, 7 and 8 are present in rat uterus. The relative abundance of rGST 8-8 in the gravid rat uterus was found to be about three-fold higher as compared with that previously seen in rat liver. Higher relative abundance of rGST8-8 in gravid rat uterus suggests that it may play a protective role against the deleterious effects of lipid peroxidation during gestation.