Aim:To analyze the role of cytosolic glutathione S-transferases (cGSTs) and membrane-associated cytosolic GSTs(macGSTs) in prostaglandin biosynthesis and to evaluate the possible interaction between glutathione S-transferases(GSTs) and cyclooxygenase (COX) in vitro.Methods:SDS-PAGE analysis was undertaken for characterization ofGSTs,thin layer chromatography (TLC) to monitor the effect of GSTs on prostaglandin biosynthesis from arachi-donic acid (AA) and spectrophotometric assays were done for measuring activity levels of COX and GSTs.Results:SDS-PAGE analysis indicates that macGSTs have molecular weights in the range of 25-28 kDa.In a coupled assayinvolving GSTs,arachidonic acid and cyclooxygenase-1,rat testicular macGSTs produced prostaglandin E2 and F2~,while the cGSTs caused the generation of prostaglandin D2,E2 and F_(2α).In vitro interaction studies on GSTs and COXat the protein level have shown dose-dependent inhibition of COX activity by macGSTs and vice versa.This effect,however,is not seen with cGSTs.The inhibitory effect of COX on macGST activity was relieved with increasingconcentrations of reduced glutathione (GSH) but not with 1-chloro 2,4-dinitrobenzene (CDNB).The inhibition ofCOX by macGSTs,on the other hand,was potentiated by glutathione.Conclusion:We isolated and purified macGSTsand cGSTs from rat testis and analyzed their involvement in prostaglandin biosynthesis.These studies reveal a revers-ible functional interaction between macGSTs and COX in vitro,with possible interactions between them at the GSHbinding site of macGSTs. Aim: To analyze the role of cytosolic glutathione S-transferases (cGSTs) and membrane-associated cytosolic GSTs (macGSTs) in prostaglandin biosynthesis and to evaluate the possible interaction between glutathione S-transferases (GSTs) and cyclooxygenase (COX) in vitro. Methods : SDS-PAGE analysis was undertaken for characterization of GSTs, thin layer chromatography (TLC) to monitor the effect of GSTs on prostaglandin biosynthesis from arachi-donic acid (AA) and spectrophotometric assays were done for measuring activity levels of COX and GSTs.Results: SDS-PAGE analysis indicates that macGSTs have molecular weights in the range of 25-28 kDa. In a coupled assay of vSTGs, arachidonic acid and cyclooxygenase-1, rat testicular macGSTs produced prostaglandin E2 and F2 ~, while the cGSTs caused the generation of prostaglandin D2, E2 and F_ (2α). In vitro interaction studies on GSTs and COXat the protein level have shown dose-dependent inhibition of COX activity by macGSTs and vice versa. This effect, howe The inhibitory effect of COX on macGST activity was relieved with increasing concentrations of reduced glutathione (GSH) but not with 1-chloro 2,4-dinitrobenzene (CDNB). The inhibition of COX by macGSTs, on the other hand, was potentiated by glutathione.Conclusion: We isolated and purified macGSTs and cGSTs from rat testis and analyzed their involvement in prostaglandin biosynthesis. These studies reveal a revers-ible functional interaction between macGSTs and COX in vitro, with possible interactions between them at the GSHbinding site of macGSTs.