Characterization of house fly microsomal mixed function oxidases: Inhibition by juvenile hormone I and piperonyl butoxide

Abstract

The microsomal mixed function oxidase system of the house fly ( Musca domestica [L.]) was characterized with respect to N-demethylation of p-chloromethylaniline, O-demethylation of methoxyresorufin, epoxidation of aldrin and the formation of a metabolite-cytochrome P-450 complex during oxidation of piperonyl butoxide (PB). The inhibition of these reactions by juvenile hormone I ( E,E cis methyl 10, 11-epoxy-7-ethyl-3,11-dimethyl-2,6-tricecadienoate JH-I) was competitive for the N-demethylase, epoxidase and the formation of the PB metabolite-complex. Non-competitive inhibition was observed for the O-demethylase. The inhibition of these reactions by JH-I provides evidence that the mixed function oxidase system participates in the degradation of juvenile hormone, and that the juvenile hormone-like properties of PB and other methylenedioxyphenyl compounds are derived from their inhibition of this degradation. The PB metabolite-cytochrome P-450 complex has 2 absorbance maxima in the reduced form (427 and 455 nm), and a single absorbance maximum in the oxidized form (438 nm). pH affected the extinction of the 427 and 455 nm absorbance bands. The pH equilibrium point was 8.3 for the reduced PB metabolite complex, and 9.5 for ethylisocyanide. In addition, the PB metabolite complex could be generated in vivo.