Metabolites of L-[³⁵S]Cysteine Injected into the Peritoneal Cavity of Rainbow Trout

Abstract

To clarify the pathway from cysteine to taurine in rainbow trout, radioactive L-cysteine was injected into the peritoneal cavity of fish and its subsequent metabolites were traced. The distribution of metabolites derived from radioactive cysteine was examined in the whole fish body and in the excreta. Taurine, hypotaurine, and sulfate were found to be major metabolites in the acid-soluble fraction of the fish body. A large amount of these metabolites was excreted within the first 24h after the injection of radioactive L-cysteine. These findings indicate that cysteine in the fish body is metabolized rapidly. The amount of sulfate produced in rainbow trout was about one half that of taurine plus hypotaurine. As evidenced by the formation of sulfate, presumably there is a metabolic pathway through cysteine sulfinate in rainbow trout.