Abstract
The successful use of CYP1A1 as a biomarker of exposure to polynuclear aromatic hydrocarbon in vertebrates lead to a chase for it in marine bivalves. Nevertheless, published results are mostly inconclusive, even with molecular approaches, and there is no clear evidence of a bivalve CYP1A1. Phylogeny of P450 suggests that bivalves could have evolved their own CYP enzymes. Apparently, they even lack the AhR pathway. New sequences from the oyster Crassostrea rhizophorae exhibited little homology to known CYP1A1 but revealed a new CYP2-like gene. Finally, the low activity of the P450 system could be explained by alternative detoxification mechanisms such as the highly active MDR system.