Phenobarbital Induction of UDP-glucosyltransferase Activity in Drosophila melanogaster Meigen

Abstract

The inducibility of UDP-glucosyltransferase activities towards the exogenous substrates 1-naphthol and 2-naphthol and the endogenous metabolite xanthurenic acid was demonstrated in Drosophila melanogaster Meigen larvae and adults using phenobarbital as an inducer. In adults, a 3.5-fold increase of glucosyltransferase activity toward xanthurenic acid and a 2.0-fold increase of the activity toward exogenous substrates (1-naphthol and 2-naphthol) was found. In larvae, maximum induction of all three UDP-glucosyltransferase activities (2.5-fold and 1.5-fold increase of the activity toward the exogenous and endogenous substrates, respectively) was achieved when insects, reared on solid medium, were exposed to phenobarbital for 24 h. However, a 24-h exposure to inducer on liquid medium yielded the same level of induction as in solid medium only for xanthurenic acid:UDP-glucosyltransferase activity. Repression of the activities toward exogenous substrates also was noticed. On this medium, comparable induction to that detected on solid medium was found when inducer exposure was reduced to 2.5 h. According to the observed variation resulting from the different conditions of phenobarbital treatment, a differential induction of UDP-glucosyltransferase isoenzymes also was demonstrated. After 2.5 h of inducer exposure, three isoenzymes (every one specific for each of the three analysed substrates) were detected; whereas, after 24 h of inducer treatment, only one isoenzyme, specific for xanthurenic acid, was detected.