. "Catalysis of the reaction: succinate + ubiquinone = fumarate + ubiquinol." . . . "complex II" . "succinic dehydrogenase activity" . "succinate dehydrogenase (ubiquinone) activity" . "fumarate reductase complex (i.e. FRD, involved in anaerobic respiration, repressed in aerobic respiration)" . "menaquinol: fumarate oxidoreductase activity" . "quinol:fumarate oxidoreductase activity" . "succinate dehydrogenase complex (i. e. SDH, involved in aerobic respiration, repressed in anaerobic respiration)" . "succinate:ubiquinone oxidoreductase activity" . . . .