Biotransformation enzymes in marine organisms: Implications for detoxification of dietary allelochemicals.

摘要

Biotransformation is well established in terrestrial systems as a mechanism for metabolizing dietary allelochemicals. Numerous marine organisms also feed on allelochemically-rich prey, but the mechanisms by which they handle these potentially toxic lipophilic compounds are unknown. This study investigated the significance of biotransformation, or detoxification, of dietary allelochemicals in marine organisms. Using predation on allelochemically-rich gorgonian corals as a model system, I examined the levels of cytochrome P450 monooxygenases and glutathione transferases in the ovulid gastropod, Cyphoma gibbosum, and the butterflyfish, Chaetodon capistratus.; Cyphoma gibbosum, a specialist gorgonian predator, had very low to non-detectable levels of digestive gland P450. Alternatively, very high levels of glutathione transferase (GST) were detected in C. gibbosum (2.76 to 4.05 {dollar}{bsol}mu{dollar}mol min{dollar}{bsol}sp{lcub}-1{rcub}{bsol}rm{lcub}mg{rcub}{bsol}sp{lcub}-1{rcub}),{dollar} ranking it among the highest ever reported. This result suggests that glutathione conjugation is a primary biotransformation mechanisms in C. gibbosum.; Chaetodon capistratus, a generalist predator of gorgonians and other anthozoans, had higher levels of total P450 and GST than reported in most other teleosts. No significant differences were detected in P450 content (0.501 to 0.821 nmol mg{dollar}{bsol}sp{lcub}-1{rcub}{dollar}) or GST activity (2.81 to 3.12 {dollar}{bsol}mu{dollar}mol min{dollar}{bsol}sp{lcub}-1{rcub}{dollar}mg{dollar}{bsol}sp{lcub}-1{rcub}{dollar}) between butterflyfish collected from an anthropogenically-impacted site in Florida and a pristine site in Belize. Low ethoxyresorufin O-deethylase (EROD) activity and low CYP1A content (the major PAH-inducible P450 isozyme and EROD catalyst) indicated that high levels of P450 and GST in C. capistratus could not be accounted for by PAH or PCB contamination.; Biotransformation enzymes in butterflyfish were further investigated by comparing C. capistratus with, C. ocellatus and C. striatus, two sympatric congeners that do not feed on gorgonians. Chaetodon capistratus had significantly more total P450 and GST as well as a larger hepatic index and more microsomal protein g{dollar}{bsol}sp{lcub}-1{rcub}{dollar} liver. Two P450 isozymes which are believed to have evolved in response to dietary allelochemicals, CYP2B and CYP3A, were 2 to 10-fold and 2 to 20-fold higher, respectively, in C. capistratus.; This research demonstrates that predators of allelochemically-rich gorgonian corals have high levels of biotransformation enzymes. This suggests that biotransformation may be a significant component of predator-prey and plant-herbivore interactions in the marine environment.