The Saccharomyces cerevisiae succinate-ubiquinone reductase contains a stoichiometric amount of cytochrome b562

The Saccharomyces cerevisiae succinate-ubiquinone reductase or succinate dehydrogenase (SDH) is a tetramer of non-equivalent subunits encoded by the SDH1, SDH2, SDH3, and SDH4 gents, In most organisms, SDH contains one or two endogenous h-type hemes. However, it is widely believed that the yeast SDH does not contain heme. In this report, we demonstrate the presence of a stoichiometric amount of cytochrome b(562) in the yeast SDH. The cytochrome is detected as a peak present in fumarate-oxidized, dithionite-reduced mitochondria. The peak is centered at 562 nm and is present at a heme:covalent FAD molar ratio of 0.92+/-0.11, The cytochrome is not detectable in mitochondria isolated from SDH3 and SDH4 deletion strains. These observations strongly support our conclusion that cytochrome b(562) is a component of the yeast SDH. (C) 1999 Federation of European Biochemical Societies.