TISSUE DISTRIBUTION OF MICROSOMAL CYTOCHROME-P-450 MONOOXYGENASES AND THEIR INDUCIBILITY BY PHENOBARBITAL IN HOUSE-FLY, MUSCA-DOMESTICA L

The tissue distribution of cytochrome P-450 microsomal monooxygenases are known to vary between insect species, but have not been reported from house fly (Musca domestica L.). We investigated the levels of cytochrome P-450s, cytochrome b5, cytochrome P-450 reductase, cytochrome P-450ipr and 4 cytochrome P-450 monooxygenase activities in the abdominal tissues from house fly and the relative responsiveness of individual tissues to the monooxygenase inducer phenobarbital (PB). The monooxygenase activity of the whole abdomen is primarily due to activities in the fat bodies, proximal intestine and Malpighian tubules. In general, PB induces the monooxygenases in most tissues, although the level of induction varies between tissues and assays. The largest induction was seen in the fat bodies for 7-ethoxycoumarin o-deethylation and aldrin epoxidation assays where PB caused > 50-fold increase in activity. Our results clearly indicate that although the whole abdomen generally reflects an average of the individual tissues, the monooxygenase activities and responsiveness to induction vary dramatically from one tissue to another. The pattern of tissue distribution of monooxygenases in the house fly relative to other insects is discussed.