A fission yeast gene for mitochondrial sulfide oxidation

A cadmium-hypersensitive mutant of the fission yeast Schizosaccharomyces po mbe was found to accumulate abnormally high levels of sulfide. The gene req uired for normal regulation of sulfide levels, hmt2(+), was cloned by compl ementation of the cadmium-hypersensitive phenotype of the mutant. Cell frac tionation and immunocytochemistry indicated that HMT2 protein is localized to mitochondria, Sequence analysis revealed homology between HMT2 and sulfi de dehydrogenases from photosynthetic bacteria. HMT2 protein, produced in a nd purified from Escherichia coli, was soluble, bound FAD, and catalyzed th e reduction of quinone (coenzyme Q(2)) by sulfide. HMT2 activity was also d etected in isolated fission yeast mitochondria. We propose that HMT2 functi ons as a sulfide:quinone oxidoreductase. Homologous enzymes may be widespre ad in higher organisms, as sulfide-oxidizing activities have been described previously in animal mitochondria, and genes of unknown function, but with similarity to hmt2(+), are present in the genomes of flies, worms, rats, m ice, and humans.