title: Catalytic properties of CYP1A isoforms in the liver of an agnathan (Lampetra fluviatilis) and two species of teleost (Pleuronectes flesus, Anguilla anguilla).
abstract: The catalytic activity of CYP1A isoforms and the effect of mammalian CYP1A-specific inhibitors in liver S9 fractions were studied in an agnathan (River lamprey, Lampetra fluviatilis, 30-33 cm) and in two species of teleost fish (European flounder, Pleuronectes flesus, 11-18 cm and common eel, Anguilla anguilla, 31-48 cm). Ethoxyresorufin O-deethylation (EROD), caffeine N-demethylation/C-oxidation and phenacetin O-deethylation (POD) activity increased 3-4-fold in flounders and 17-46-fold in eels, 5 days after fish were injected (i.p.) with 100 mg kg(-1) benzo(a)pyrene (B[a]P). In lampreys, basal EROD activity was very low and no increase in activity was observed following exposure to B[a]P. While the apparent Michaelis constant (K(m)) for each assay showed only small changes after B[a]P injection, maximum reaction velocity (V(max)) values increased by up to 19- and 84-fold for EROD activity, 4- and 35-fold for caffeine-related metabolism and 4- and 19-fold for POD activity in flounders and eels, respectively. The mammalian CYP1A2 inhibitor furafylline (50 microM-1 mM) reduced activity in the EROD, caffeine and POD assays to 65, 21 and 20% of control values in flounders and to 85, 10 and 5% of control values in eels, respectively. By contrast, low concentrations (0.025-0.050 microM) of the mammalian CYP1A1 inhibitor ellipticine completely abolished EROD activity, but had no effect (up to 1 mM) on caffeine metabolism or POD activity in either species. While the inhibitor studies strongly suggest that two separate enzymes are present in flounders and eels, the monophasic Michaelis-Menten kinetics obtained in all the assays imply that only a single CYP1A protein is present that has substrate and inhibitor specificities characteristic of both mammalian CYP1A1 and CYP1A2 isoforms.
authors.affiliation: Department of Biology, Johns Hopkins University, 3400 North Charles Street, Baltimore MD 21113, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Rotchell
authors.forename: G B
authors.initials: GB
authors.lastname: Steventon
authors.forename: D J
authors.initials: DJ
authors.lastname: Bird
mesh_terms: D000811:Anguilla / Q000502:physiology*; D000818:Animals; D002110:Caffeine / Q000008:administration & dosage / Q000378:metabolism; D000697:Central Nervous System Stimulants / Q000008:administration & dosage / Q000378:metabolism; D019363:Cytochrome P-450 CYP1A1 / Q000737:chemistry / Q000378:metabolism*; D005432:Flounder / Q000502:physiology*; D007527:Isoenzymes; D007700:Kinetics; D007798:Lampreys / Q000502:physiology*; D008099:Liver / Q000201:enzymology; D010084:Oxidation-Reduction
chemical_list: D000697:Central Nervous System Stimulants; D007527:Isoenzymes; D002110:Caffeine; D019363:Cytochrome P-450 CYP1A1