The occurrence of cytochrome P-450 and aryl hydrocarbon hydroxylase activity in drosophila melanogaster microsomes, and the importance of this metabolizing capacity for the screening of carcinogenic and mutagenic properties of foreign compounds

Abstract

Abstract The presence of cytochrome P-450 and aryl hydrocarbon hydroxylase activity in microsomes prepared from three strains of Drosophila melanogaster was investigated. The first microsomal preparations, for which mortar pounding was used to homogenize the insects, indicated the occurrence of cytochrome P-450, as concluded from carbon monoxide difference spectra, exhibiting an absorbance maximum at 452 nm. As the reproducibility of the mortar procedure was irregular, a new homogenization procedure was developed, using glass marbles. This method led to a better reproducibility and an increase in the quality of the carbon monoxide difference spectra. An empirical correction by a computer was used for analysis of the spectra. Aryl hydrocarbon hydroxylase activity, one of the expressions of the mixed function oxidase system mediated by cytochrome P-450, was studied by using benzo(a)pyrene as substrate and measuring enzymically produced 3-hydroxy-benzo(a)pyrene. The observed activity was NADPH dependent and was absent (i) when NADH was given as cofactor, (ii) when the microsomes were destroyed by boiling, and (iii) when they were deteriorated by treatment with deoxycholate. These findings provide the basis for further investigations, by which a better understanding of the metabolizing capacity of Drosophila can make this species even more meaningful for the screening of pre-carcinogens and indirectly acting mutagens.