Methylenedioxyphenyl complexes with microsomal cytochrome P-450: In vivo complex formation in rat liver and in midgut tissues of the Southern armyworm (Spodoptera eridania)

The capacity of several methylenedioxyphenyl insecticide synergists to generate metabolite complexes with cytochrome P-450 was studied in midgut tissues of the Southern armyworm (Spodoptera eridania). Examination of the NADH-reduced versus oxidized spectra from methylene-dioxyphenyl-induced midgut indicated that isosafrole, dihydrosafrole, and 4-ethoxy-1,2-methylenedioxybenzene generated metabolite complexes with a principal absorbance maximum at 427 nm and smaller absorbance maxima near 460 and 556 nm. Further studies with 2-n-heptylbenzimidazole showed that the complex between insect cytochrome P-450 and dihydrosafrole was unusually resistant to displacement. Initial rates of complex displacement in insect microsomes were found to be approximately an order of magnitude slower than those of the corresponding complexes in rat hepatic microsomes. Nevertheless, with the exception of the dihydrosafrole complex in insect microsomes, the “time to half-maximal displacement” parameter was found to be very similar for each complex. These findings indicate that the formation of dissociable complexes between cytochrome P-450 and the methylenedioxyphenyl metabolite occurs in both insect midgut and rat hepatic microsomes after in vivo exposure. From the present study it would appear that dihydrosafrole may constitute a useful probe to distinguish binding sites within insect and mammalian cytochrome P-450.