Catalytic properties of CYP1A isoforms in the liver of an agnathan (Lampetra fluviatilis) and two species of teleost (Pleuronectes flesus, Anguilla anguilla)

The catalytic activity of CYP1A isoforms and the effect of mammalian CYP1A- specific inhibitors in liver S9 fractions were studied in an agnathan (Rive r lamprey, Lampetra fluviatilis, 30-33 cm) and in two species of teleost fi sh (European flounder. Pleuronectes flesus, 11-18 cm and common eel, Anguil la anguilla, 31-45 cm). Ethoxyresorufin O-deethylation (EROD), caffeine N-d emethylation/C-oxidation and phenacetin O-deethylation (POD) activity incre ased 3-4-fold in flounders and 17-46-fold in eels, 5 days after fish were i njected (i.p.) with 100 mg kg(-1) benzo(a)pyrene (B[a]P). In lampreys, basa l EROD activity was very low and no increase in activity was observed follo wing exposure to B[a]P. While the apparent Michaelis constant (K-m) for eac h assay showed only small changes after B[a]P injection, maximum-reaction v elocity (V-max) values increased by up to 19- acid 84-fold for EROD activit y, 4- and 35-fold for caffeine-related metabolism and 4- and 19-fold for PO D activity in flounders and eels, respectively. The mammalian CYP1A2 inhibi tor furafylline (50 mu M-1 mM) reduced activity in the EROD, caffeine and P OD assays to 65, 21 and 20% of control values in flounders and to 85, 10 an d 5% of control values in eels, respectively. By contrast, low concentratio ns (0.025-0.050 mu M) of the mammalian CYP1A1 inhibitor ellipticine complet ely abolished EROD activity, but had no effect (up to 1 mM) on caffeine met abolism or POD activity in either species. While the inhibitor studies stro ngly suggest that two separate enzymes are present in flounders and eels, t he monophasic Michaelis-Menten kinetics obtained in all the assays imply th at only a single CYP1A protein is present that has substrate and inhibitor specificities characteristic bf both mammalian CYP1A1 and CYP1A2 isoforms. (C) 2000 Elsevier Science Inc. All rights reserved.