Biochemical Evidence that Winter Flounder (Pseudopleuronectes americanus) have Induced Hepatic Cytochrome P-450-Dependent Monooxygenase Activities

Abstract

Livers from winter flounder (Pseudopleuronectes americanus) captured near Mount Desert Island, Maine, showed marked variation in hepatic benzo[a]pyrene hydroxylase (AHH; from 0.04 to 8.8 FU∙min−1∙mg protein−1) and 7-ethoxyresorufin deethylase activities (7-ERD; from < 2 to 1165 pmol∙min−1∙mg protein−1), and a dichotomy in the effect of 7,8-benzoflavone (ANF) added in vitro on AHH activity. Based on this ANF effect, the flounder could be divided into two groups. One group had high 7-ERD activity and high AHH activity which was inhibited by ANF; the other group had low 7-ERD activity and low AHH activity which was enhanced by ANF. Sex, weight, length, liver weight, gonad weight/body weight ratio, and liver/body weight ratio explained only a small part of the variability in hepatic AHH activities. Electrophoretograms of hepatic microsomes from flounder treated with 1,2,3,4-dibenzanthracene (DBA) or 5,6-benzoflavone (βNF) showed a novel or enriched polypeptide species present near 57 000 daltons, in the molecular weight (MW) range of known cytochrome P-450 isozymes. A polypeptide of similar MW was only faintly discernable in liver microsomes from untreated flounder whose hepatic AHH activity was much lower than that of the treated flounder, whereas a band of this MW was prominent in hepatic microsomes from untreated flounder with high hepatic AHH activity. These results suggest that many of the winter flounder captured near Mount Desert Island, Maine have induced hepatic monooxygenase activity due to exposure to PAH or PAH-like inducers present in their natural habitat.