title: Catalytic function of avian cytochrome P450 1A4 and 1A5 (CYP1A4 and CYP1A5) enzymes heterologously expressed using in vitro yeast system.
abstract: The present study clarifies the enzymatic properties of two avian cytochrome P4501A (CYP1A) paralogs, CYP1A4 and 1A5, using a yeast-based vector system. Recombinant CYP1A4 and 1A5 proteins from common cormorant (Phalacrocorax carbo) were expressed in yeast cells, and showed typical reduced CO-difference spectra with a peak at 446 nm. Kinetic analysis of O-dealkylase of methoxy-, ethoxy-, pentoxy- and benzyloxyresorufin catalyzed by the CYP1A enzymes revealed that Vmax value for ethoxyresorufin-O-deethylase (EROD) activity was much higher than that for the other three O-dealkylase activities for both isozymes. Interestingly, remarkable substrate specificity of the CYP1As was observed for O-dealkylation of benzyloxyresorufin and methoxyresorufin; CYP1A4 was highly specific for catalyzing benzyloxyresorufin-O-debenzylase activity, whereas CYP1A5 was more efficient in catalyzing methoxyresorufin-O-demethylase activity. The present study also measured CYP1A-dependent EROD activity in the presence of 2,3,7,8-tetrachlorodibenzofuran (TCDF) to evaluate the ability of this dioxin-like congener to inhibit the EROD activity. One hundred nanomolar TCDF noncompetitively inhibited CYP1A5-dependent EROD activity, although no inhibitory effect was detected for CYP1A4-dependent EROD activity. These results indicate that the avian CYP1A paralogs have different affinities for substrate and inhibitor, thus suggesting their distinct physiological and toxicological roles.
authors: Division of Ecotoxicology, Center for Marine Environmental Studies, Ehime University, 2-5 Bunkyo-cho, Matsuyama, Japan.
authors: Akira
authors: A
authors: Kubota
authors: Hisato
authors: H
authors: Iwata
authors: Eun-Young
authors: EY
authors: Kim
mesh_terms: D000818:Animals; D030161:Avian Proteins / Q000235:genetics* / Q000378:metabolism*; D001572:Benzofurans / Q000494:pharmacology; D001717:Birds / Q000235:genetics*; D019363:Cytochrome P-450 CYP1A1 / Q000187:drug effects / Q000378:metabolism; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics* / Q000378:metabolism*; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D014874:Water Pollutants, Chemical / Q000494:pharmacology; D015003:Yeasts / Q000235:genetics*
chemical_list: D030161:Avian Proteins; D001572:Benzofurans; D014874:Water Pollutants, Chemical; D003577:Cytochrome P-450 Enzyme System; D019363:Cytochrome P-450 CYP1A1; C014211:2,3,7,8-tetrachlorodibenzofuran