Tissue distribution of the enzyme rhodanese in four cyprinid fish species

Rhodanese (thiosulfate: cyanide sulfurtransferase; EC. 2.8.1.1) is a ubiquitous enzyme present in both prokaryotes and eukaryotes. Its physiological function is controversial, but it is believed that the enzyme plays a central role in cyanide detoxification. The purpose of this investigation was to determine and compare the pattern of tissue distribution of rhodanese in different tissues of four cultured cyprinid fish species, including the common carp, grass carp, silver carp, and bighead carp. Rhodanese activity was detected in all tissues studied, albeit in different amounts. Specific activities (enzyme units per milligram protein) of rhodanese in different tissues of the common carp, grass carp, silver carp, and bighead carp range from 0.022 to 0.162, 0.018 to 0.215, 0.038 to 0.180, and 0.034 to 0.221, respectively. The highest activity of rhodanese in all four species was observed in the liver and kidney, followed by the gill and intestine, while the lowest activity was present in the brain. Inter-species differences were not observed in the level of the enzyme in different tissues. The results of this study may indicate the involvement of rhodanese in cyanide detoxification in tissues that have greater potential to be exposed to higher levels of cyanide. However, the widespread tissue distribution of rhodanese suggests additional important biological functions for the enzyme besides cyanide detoxification.