Six isoenzymes of glutathione S-transferase (GST) present in mouse lung have been purified and characterized. GST I (pI 9.8) is a dimer of Mr-26,500 subunits and GST II is a heterodimer of Mr-26,500 and -22,000 subunits, and GST III (pI 7.9) and IV (pI 6.4) are dimers of Mr-24,500 subunits. GST V (pI 5.7) is a heterodimer of Mr-24,500 and -23,000 subunits, whereas GST VI (pI 4.9) is a dimer of Mr-23,000 subunits. Immunological studies indicate that the Mr-24,500 subunits present in GST III (pI 7.9) are distinct from those present in GST IV (pI 6.4) and V (pI 5.7). Structural and immunological studies provide evidence that at least five distinct types of subunits in their different binary combinations give rise to various GST isoenzymes of mouse lung. These isoenzymes express varying degrees of catalytic activities towards a wide range of electrophilic substrates including benzo[a]pyrene 7,8-oxide and benzo[a]pyrene 4,5-oxide. The dietary antioxidant t-butylated hydroxyanisole (BHA) preferentially induces GST II and III. Also, these two isoenzymes selectively bind benzo[a]pyrene (B[a]P) metabolites, indicating that they play an important physiological role in the detoxification of B[a]P metabolites. The preferential induction of the GST isoenzymes involved in the detoxification of activated B[a]P metabolites indicates that the anti-neoplastic activity of BHA against B[a]P-induced neoplasia in mouse lung [Wattenberg (1973) J. Natl. Cancer Inst. 50, 1541-1544] may be due to the enhanced detoxification of B[a]P metabolites.
