Two distinct, membrane-bound, FAD-containing enzymes are responsible for the catalysis of fumarate and succinate interconversion; the fumarate reductase is used in anaerobic growth, and the succinate dehydrogenase is used in aerobic growth. a quinone + succinate = a quinol + fumarate Carbohydrate metabolism; tricarboxylic acid cycle; fumarate from succinate (bacterial route): step 1/1. Part of an enzyme complex containing four subunits: a flavoprotein, an iron-sulfur, cytochrome b-556, and a hydrophobic anchor protein. Belongs to the FAD-dependent oxidoreductase 2 family. FRD/SDH subfamily.