Catalytic and immunologic characterization of hepatic and lung cytochromes P450 in the polar bear.
The Arctic Ocean is subject to considerable influx of anthropogenic pollutants including halogenated organic compounds. The polar bear (Ursus maritimus) is at the top of the arctic marine food web and is an ideal species for monitoring the level and distribution of contaminants in the arctic ecosystem. As the first step in the development of a biological method for assessing the functional exposure of polar bears to xenobiotics, biochemical studies were undertaken to characterize polar bear cytochromes P450. Liver and lung samples were obtained in the field from four, freshly killed, adult, male polar bears and immediately frozen at -196 degrees. Microsomes were subsequently prepared and used for the measurement of total cytochrome P450 content and aminopyrine N-demethylase, benzphetamine N-demethylase, ethylmorphine N-demethylase, p-nitrophenol hydroxylase and testosterone hydroxylase activities. Immunoblots containing hepatic and lung microsomal samples from the polar bears were probed using antibodies generated against several purified rat cytochrome P450 isozymes. Monoclonal antibody to rat cytochrome P450 1A1 and polyclonal antibodies to rat cytochromes P450 1A1, 2B1 and 3A1, as well as antibody to epoxide hydrolase, cross-reacted to varying degrees with polar bear hepatic microsomes. In addition, polyspecific antibody to the rat cytochrome P450 2C subfamily gave several immunostained protein bands, but antibodies specific to rat cytochrome P450 2C7 and 2C13 did not react, while antibody specific to cytochrome P450 2C11 yielded an ambiguous result. Except for anticytochrome P450 2B1 and polyspecific antibody to the cytochrome P450 2C subfamily, the antibodies listed above did not cross-react with polar bear lung microsomes at the protein concentrations used. The results demonstrate that polar bear liver contains multiple forms of cytochrome P450 that are catalytically active toward diverse substrates and that several of these forms are immunochemically related to rat cytochrome P450 isozymes. Immunochemical homologues of rat cytochrome P450 1A, 2B, 2C and 3A subfamilies, and of rat epoxide hydrolase are present in polar bear liver. In addition, the polar bears all had high levels of immunoreactive cytochrome P450 1A and 2B proteins, probably as a consequence of induction by environmental contaminants.
Bandiera
S M
SM
Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, Canada.
Torok
S M
SM
Lin
S
S
Ramsay
M A
MA
Norstrom
R J
RJ
D000818:Animals; D000906:Antibodies / Q000276:immunology; D001110:Arctic Regions; D002384:Catalysis; D003429:Cross Reactions; D003577:Cytochrome P-450 Enzyme System / Q000032:analysis* / Q000276:immunology; D004463:Ecology; D015151:Immunoblotting; D008099:Liver / Q000201:enzymology*; D008168:Lung / Q000201:enzymology*; D008297:Male; D008861:Microsomes / Q000201:enzymology; D051381:Rats; D001503:Ursidae / Q000378:metabolism*; D015262:Xenobiotics / Q000378:metabolism*
D000906:Antibodies; D015262:Xenobiotics; D003577:Cytochrome P-450 Enzyme System