Flavoprotein (FP) subunit of succinate dehydrogenase (SDH) that is involved in complex II of the mitochondrial electron transport chain and is responsible for transferring electrons from succinate to ubiquinone (coenzyme Q). a quinone + succinate = a quinol + fumarate Carbohydrate metabolism; tricarboxylic acid cycle; fumarate from succinate (eukaryal route): step 1/1. Component of complex II composed of eight subunits in plants: four classical SDH subunits SDH1, SDH2, SDH3 and SDH4 (a flavoprotein (FP), an iron-sulfur protein (IP), and a cytochrome b composed of a large and a small subunit.), as well as four subunits unknown in mitochondria from bacteria and heterotrophic eukaryotes. Belongs to the FAD-dependent oxidoreductase 2 family. FRD/SDH subfamily.