The cytochrome P-450 enzyme system in the fruit fly, Drosophila melanogaster, was shown to be inducible, to consist of several isozymes and to have the capacity to metabolize a variety of substrates, thus resembling the corresponding mammalian system. These similarities strengthens the value of Drosophila test systems for the detection of indirect carcinogens and mutagens. Quantitative and qualitative differences did, however, occur particulary in the metabolism of and induction by polycyclic aromatic hydrocarbons.

The cytochrome P-450 system was generally more active in adult flies when compared with larvae, but the capacity to deethylate 7-ethoxycoumarin was equal in the two stages, indicating differences in the temporal control of the cytochrome P-450 isozymes. SDS-polyacrylamide gel electrophoresis of microso- mes from larvae and adult flies also revealed stage-dependent increases in specific protein band in the heme-containing area (mw 45—60.000) in response to pretreatment with the cytochrome P-450 inducers phénobarbital, PCB and ß- naphthoflavone.

A substantial genetic varation in the capacity to metabolize different substrates and in the response to enzyme induction was observed between Drosophila strains with different geographic origin and history of xenobiotic exposure. Variation between strains was also discernible in the pattern of the specific protein bands, demonstrated by SDS-polyacrylamide gel electrophoresis of the microsomal fractins. This study has revealed four to five genes determining different cytochrome P-450-dependent activities in Drosophila, located at different places on the second and third chromosomes.