Hepatic cysteinesulphinate decarboxylase activity in fish

Abstract

In order to elucidate the participation of l-cysteinesulphinate decarboxylase (CSD) in taurine synthesis in Japanese flounder, and the synthetic ability of taurine in other fish species, hepatic (or hepatopancreatic) CSD activities of several fish species were compared. Enzyme activity was determined by measuring the production of hypotaurine during an incubation of crude enzyme preparation with l-cysteinesulphinate as a substrate. HPLC was used for the analysis of hypotaurine. The enzyme activities of fish were lower than those of mammals. Japanese flounder Paralichthys olivaceus (Temminck et Schlegel) showed half the activity of rainbow trout (Oncorhynchus mykiss Walbaum). As activity was almost constant throughout the fish growth cycle, CSD does not seem to be responsible for low production of taurine in juvenile Japanese flounder. On the other hand, CSD activity was not present in yellowtail (Seriola quinqueradiata Temminck et Schlegel), bluefin tuna Thunnus thynus (Linnaeus) or skipjack (Katsuwonus pelamis (Linnaeus)). The inability to synthesize taurine and the possible dietary requirement for taurine is suggested in these fish species.