Membrane-anchoring 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). Mediates resistance to enteropathogenic E.coli infection (By similarity). The heme is bound between the two transmembrane subunits. Carbohydrate metabolism; tricarboxylic acid cycle. Component of complex II composed of four subunits: a flavoprotein (FP), iron-sulfur protein (IP), and a cytochrome b560 composed of two transmembrane proteins. Is expressed at a constant level throughout development. Belongs to the cytochrome b560 family.