Tridiphane [2-(3,5-dichlorophenyl)-2-(2,2,2-trichloroethyl)oxirane] an atrazine synergist: Enzymatic conversion to a potent glutathione S-transferase inhibitor

Glutathione S-transferases (GST) from corn, giant foxtail, onion, pea, house fly, and equine liver catalyzed conjugation of tridiphane with glutathione (GSH). The conjugate was characterized by soft ionization mass spectral methods. Tridiphane and the GSH conjugate of tridiphane both inhibited GSH conjugation of atrazine in vitro (corn and giant foxtail). Tridiphane did not inhibit GSH conjugation of 1-chloro-2,4-dinitrobenzene (CDNB) in corn or giant foxtail; however, the GSH conjugate of tridiphane was a competitive inhibitor with respect to GSH and was four times more effective with extracts from giant foxtail (K_i = 2 μM) than from corn (K_i = 8 μM). The GSH conjugate of tridiphane inhibited a variety of GST enzymes with several different substrates. When compared to other inhibitors of GST, only triphenyl tin chloride was more effective than the GSH conjugate of tridiphane in inhibition of GST from giant foxtail. Both GST and GSH decreased in corn and increased in giant foxtail as tissues matured. The catabolism of the GSH conjugate of tridiphane was compared in crude enzyme systems from corn, giant foxtail, and onion. The rate of catabolism was much greater in extracts from corn leaves than from giant foxtail leaves. Inhibition of GSH conjugation of CDNB was reversed as the GSH conjugate of tridiphane was catabolized. The possibility that synergism of atrazine toxicity by tridiphane is mediated by conversion of tridiphane to a GSH conjugate is discussed in relationship to the relative rates of GSH conjugation of tridiphane and atrazine, concentrations of GSH, K_i values, tissue age, and stability of the conjugate in different tissues.