Figure 1.

Structure, maturation, and assembly of succinate dehydrogenase (SDH) complex. The SDH complex, or mitochondrial complex II, sits within the inner mitochondrial membrane and is included in both the tricarboxylic acid cycle (TCA) and the electron transport chain (ETC). Succinate is an enzyme that is a part of the TCA cycle and is oxidized to fumarate through SDH; this is also present in the reverse reaction. From the oxidization, two electrons are transferred to subunit A to protonate FAD to FADH₂ and release two electrons to the Fe-S clusters housed within subunit B. Assembly factors SDHAF1 and SDHAF2 assist in the maturation of subunits A and B. SDHAF1 provides Fe-S clusters to SDHB and SDHAF2 works in conjunction with dicarboxylate to stabilize the active site of SDHA. The next subunits, C and D, house heme and are responsible for ubiquinone reduction to ubiquinol. From here, ubiquinol is transferred to complex III of the ETC. The three known pseudogenes of SDHA, SDHAP1-3, are also included, whose metabolic function is still unknown.