Membrane-anchoring subunit of succinate dehydrogenase (SDH). The heme is bound between the two transmembrane subunits. Carbohydrate metabolism; tricarboxylic acid cycle. Part of an enzyme complex containing four subunits: a flavoprotein, an iron-sulfur protein, plus two membrane-anchoring proteins, SdhC and SdhD. The complex can form homotrimers. His-84 provides an axial ligand to heme b556 in the wild-type enzyme. The retention of low spin heme b556 in the SdhC 'Leu-84' mutant suggests that swapping of the heme axial ligand by His-91 or His-30 is possible. Belongs to the cytochrome b560 family.