Organic Xenobiotic Metabolism in Marine Invertebrates

Abstract

Since their heterotrophic origin, animals have been faced with a continual input of foreign compounds, so-called xenobiotics, from their food sources, e.g. polybromomethanes and alkyl halides in seaweeds (Gschwend et al. 1985) and defensive toxins in other animals (Bakus and Kawaguchi 1984); and from the attacks of predators, e.g. venoms of certain gastropods and cephalopods (Fange 1984). For example, “animal-plant warfare” is considered to be a major selective pressure in driving the evolution of some of the gene families of the biotransformation enzyme, cytochrome P-450 (Nebert et al. 1989b). Over time, additional sources of xenobiotics have included erosion of hydrocarbon-containing shales, and oil seepage from natural reservoirs (started at least 100,000 years ago) (Farrington 1985), hostile environments such as the high sulphide levels around deep sea hydrothermal vents (Vetter et al. 1987), and, in more recent years, man’s multifarious industrial and other activities (Mix 1984). Central to the defense against such an enormous and diverse number of potentially toxic compounds is an impressive array of enzymes, which function ideally to detoxify and eliminate xenobiotics from an organism. The biological significance of biotransformation enzymes is increased by the inducibility of some of them by xenobiotics, and by their metabolism of certain xenobiotics to molecular species more toxic, mutagenic or carcinogenic than the parent compound. Elaboration of the qualitative and quantitative aspects of organic xenobiotic metabolism in marine invertebrates, and the function and regulation of the enzymes involved, is important for several reasons, viz. predicting and modelling the fate and toxicity of xenobiotics in marine organisms and ecosystems (e.g. Harris et al. 1984); development of specific indices of biological effect for use in pollution monitoring and impact assessment (e.g. Malins et al. 1985; Kleinow et al. 1987; Payne et al. 1987; Bayne et al. 1988); and understanding the evolutionary relationships of the biotransformation pathways in different phylogenetic groups, and the use of the pathways in invading, or exploiting, ecological time and space to create new niches.