魚類組織中のトリメチルアミンオキシド生合成と塩分環境

抄録

The author has been paying attention to the study of osmolyte in fish. In this paper, I tried to put together a biosynthesis of trimethylamine oxide (TMO) in fish tissue in relation to saline environment with the present and previous information. TMO is one of the characteristic constituents in tissues of marine animals. A large amount of TMO occurrs particularly in cods, sharks and squids. Remarkably, the ancestral marine fish, coelacanth Latimeria chalumnae also contains large quantities of TMO. In fish, the relationship between environmental salinity and TMO content in tissue was found, that is TMO contents in the muscle increased significantly in both juveniels and adults of rainbow trout after salinity exposure. Thus, TMO is regarded as an osmolite in invertebrates and elasmobranchs, and moreover there are several reports that TMO might constitute part system for osmoregulation in marine teleost. The author has already reported that TMO concentration of fish tissue increased by feeding on the diets added with trimethylamine (TMA) and also by seawater environment Previously, the author confirmed TMA monooxygenase activity in the liver and kidney of eel, Anguilla japonica using [^<14>C]-TMA , and TMA and TMO concentrations were influenced by the dietary choline level and environmental seawater. In tilapia, Oreochromis niloticus, it was indicated that the mechanism responsible for TMO accumulation was induced by feeding a diet containing choline; i.e. TMA is microbiologically formed from dietary choline in the intestine, and the TMA thus formed is then absorbed and converted into its N-oxide form, TMO, in the liver and/or kidney. Accumulation of TMO induced by feeding a diet containing choline seemed to occur in marine fish. TMO may be synthesized through this process and accumulate mainly in the muscle in these fishes. TMO is readily produced from dietary choline and then stored mainly in the muscle even if the diet is free of both TMA and TMO. It is worth noting that both the intestinal microorganisms and the tissue oxygenase are indispensable for constructing the TMO pool in fish muscle. In addition, dietary TMO might be indirectly transferred to the muscle via microbial reduction to TMA.