Figure 3.

Succinate dehydrogenase/complex II. The oxidation of succinate to fumarate yields two electrons that subsequently reduce ubiquinone to ubiquinol. A ubiquinone binding site (UQ) at the inner mitochondrial membrane, formed by residues in SDHB, SDHC and SDHD, lies close to the SDHB 3Fe-2S redox center. Protonation of ubiquinol likely occurs at the conserved SDHD Tyr114 residue in the UQ pocket, the site of the Northern Italian founder variant p.(Tyr114Cys), which is associated with very low PPGL risk. SDHAF2 is essential for flavination and assembly of the SDH complex and prior to assembly binds at the SDHA-SDHB interface. Although depicted in the figure with regard to the discussion later in this paper, SDHAF2 has no known post-assembly role in SDH function.