A cytochrome P4501B gene from a fish, Pleuronectes platessa

Tetrapod cytochrome P4501 family (CYP1A1, CYP1A2 and CYP1B1) enzymes are mo st active in hydroxylating a variety of environmental contaminants includin g polyaromatic hydrocarbons (PAH), planar polychlorinated biphenyls and ary lamines and thus play a pivotal role in the toxicology of these compounds. Mammalian CYP1A1 and CYP1A2 genes appear to have diverged after the evoluti onary emergence of mammals, whereas fish species apparently possess only on e CYP1A family gene, and fish CYP1A enzymes exhibit properties of both of t he mammalian isoforms. We have isolated a further CYP1 family gene from a m arine flatfish (plaice; Pleuronectes platessa), which, on the basis of exon organisation and sequence similarity, can be assigned as a piscine CYP1B. Its deduced amino acid sequence shows the closest (54%) identity to mammali an CYP1B1 proteins and, on the basis of molecular modeling studies, shows a high degree of positional and structural conservation of the substrate con tacting amino acid residues in its putative active site when compared to ot her CYP1 enzymes. Phylogenetic analysis of fish and mammalian CYP1 family s equences indicates that the plaice CYP1B and mammalian CYP1B1 genes share a common ancestry. Plaice CYP1B has a more restricted tissue expression prof ile than the previously isolated plaice CYP1A, only being detectable, by No rthern blotting, in gill tissue. In contrast to CYP1A, which shows extensiv e PAM-dependent induction in a variety of tissues, plaice CYP1B appears unr esponsive to treatment with a prototypical PAM-type inducer, beta -naphthof lavone (BNF). (C) 2000 Elsevier Science B.V. All rights reserved.