Metabolism of juvenile hormone I by microsomal oxidase, esterase, and epoxide hydrase of Musca domestica and some comparisons with Phormia regina and Sarcophaga bullata

Abstract

House fly ( Musca domestica L.) microsomes prepared from larvae, pupae, or adults contain three enzyme system which can metabolize juvenile hormone I: an esterase, an oxidase, and epoxide hydrase. The presence of the oxidase is indicated by the increased metabolism when microsomes are supplemented with NADPH and by the occurrence of additional metabolites tentatively identified as products arising from oxidation of the 6, 7 double bond. Additional evidence of the activity of the oxidase system is the increased metabolism of juvenile hormone I by the NADPH-dependent system from phenobarbital-induced insects, by inhibition of the oxidation by piperonyl butoxide and carbon monoxide, and by the greater metabolism of the hormone by microsomes from insecticide-resistant (high oxidase) strains. In vivo studies of house fly adults treated with 3H-labeled juvenile hormone I reveal a pattern of metabolism similar to that seen during NADPH-supplemented in vitro metabolism. The three enzymes have somewhat different patterns of activity during the larval stage of the house fly, juvenile hormone esterase and epoxide hydrase beginning at a high level of activity in the young larvae while the juvenile hormone oxidase is low at this stage. In the late larval stage all three enzymes show increased activity followed by declines during the pupal stage and further increases in the adult stage. Comparison of in vitro enzyme levels of the house fly, flesh fly ( Sarcophaga bullata Parker), and blow fly [ Phormia regina (Meigen)] showed that, although the enzymes were present in the latter two species, their activity on a per insect basis was considerably less than that of the house fly.