Xenobiotic biotransformation in the Pacific oyster (Crassostrea gigas)

1. Oyster visceral mass and gill tissues possessed measurable flavin-containing monooxygenase (FMO) activity. 2. FMO activity was confirmed in visceral mass microsomes by oxygen uptake experiments utilizing various nitrogen and sulfur-containing chemicals along with measurement of N,N-dimethylaniline (DMA) N-oxidase and methimazole oxidation activities. DMA N-oxidase and methimazole oxidation activities also were present in gill microsomes. 3. Excluding oyster gill methimazole oxidation, there were no consistent seasonal differences in FMO activity in oyster gill or visceral mass microsomes. 4. Although lacking spectral evidence for cytochrome P-450, a peak at 418 nm was observed along with NADPH-cytochrome c reductase activity in visceral mass and gill microsomes suggesting the presence of a denatured cytochrome P-450 system. 5. NADPH-independent benzo(a)pyrene hydroxylase (BPH) activity was observed in both oyster visceral mass and gill microsomes suggesting a co-oxidation pathway possibly involving a one electron transfer of oxygen from a lipid hydroperoxide.