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 three different fish species including rainbow trout , kutum and golden grey mullet. In the three species studied, rhodanese was present in all tissues albeit in different amounts. Specific activities (enzyme units/mg protein) of rhodanese in different tissues of rainbow trout, kutum and golden grey mullet range 0.017–0.122, 0.049–0.219 and 0.062–0.258 respectively. The highest activity of rhodanese in all three species was observed in liver and kidney. Among other tissues, rhodanese specific activity of intestine and gill was considerably greater than the values of brain, heart and muscle in all studies species. Significant inter-species differences were observed in the level of enzyme in some tissues. Specific activity of rhodanese was lowest in most tissues of rainbow trout in comparison with two other species. 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.

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