Effect of sulfide toxicity on cytochrome c oxidase in liver and muscle tissue in fish species

Toxic effects of sulfide have long been recognized. However, specific physiological effects have been investigated in few metabolic systems. Much of sulfide toxicity comes from inhibition of the enzyme cytochrome c oxidase (CytOx), which catalyzes the terminal step in aerobic respiration in eukaryotes. Previous work investigated CytOx activity in the presence of sulfide in numerous plant species and showed that estuarine species were more tolerant of sulfide compared to flooding sensitive species. This suggested that varying sensitivities of CytOx to sulfide exist across organisms as an adaptive mechanism to life in highly sulfidic salt marshes. But little is known whether fish species that live in sulfide-rich environments have a similar adaptive mechanism compared to those that live in pristine environments. Objectives of this study were to examine the expression of CytOx mRNA of common carp harvested from pristine environment and compare with enzyme activity in liver and muscle of common carp, fathead minnow, and channel catfish. Cytochrome c oxidase activities were measured in tissue homogenate exposed to 0, 5, 10, 15, and 20 μM sodium sulfide. CytOx activities were significantly higher in liver compared to muscle tissues. Activities of CytOx were very sensitive to sulfide in all tissues and were near zero at 5 μM sulfide. Cytochrome c oxidase activities in all 3 species were equally sensitive to sulfide. This illustrates the potent metabolic effects of sulfide. Human physiology is also sensitive to sulfide, making the results of this study potentially useful in several contexts