Glutathione S-transferase-dependent conjugation of leukotriene a₄-methyl ester to leukotriene C₄-methyl ester in mammalian skin

The glutathione S-transferase (GST)-dependent conjugation of reduced glutathione (GSH) with leukotriene A₄ (LTA₄)-methyl ester in rodent and human skin was investigated. Incubation of [³H]LTA₄-methyl ester (1 nmole, ≈200,000 dpm) with cytosol prepared from rat, mouse and human skin or with affinity purified GST from rat skin cytosol in the presence of GSH resulted in the formation of LTC₄-methyl ester. Maximum enzyme activity was observed in rat skin followed by mouse and human skin. With heat-denatured cytosol or in the absence of GSH, the product formation was negligible. GST purified from rat skin cytosol by GSH-agarose affinity chromatography exhibited a several-fold increase in the specific activity of enzyme with 1-chloro-2,4-dinitrobenzene (55-fold), ethacrynic acid (67-fold) and LTA₄-methyl ester (12-fold) as substrates. Western blot analysis of the affinity purified GST indicated a predominant expression of the Pi class of GST isozyme followed by Mu and Alpha classes of isozymes. The formation of LTC₄-methyl ester was established by its radioactivity profile on high pressure liquid chromatography and absorption spectroscopy. These results suggest that, in addition to xenobiotic metabolism, cutaneous GSTs may also be capable of metabolizing physiological substrates such as LTA₄.