and Tyr83 of subunit D. The quinone ring is surrounded by Ile28 of subunit C and Pro160 of subunit B. These residues, along with Il209, Trp163, and Trp164 of subunit B, and Ser27 (C atom) of subunit C, form the hydrophobic environment of the quinone-binding pocket Qp. In contrast, ubiquinone binding site Q_D, which lies closer to inter-membrane space, is composed of SDHD only and has lower affinity to ubiquinone.

Succinate binding site