Figure 1.

Diagram of homodimeric cytochrome bc₁ structure describing the general mechanism of enzymatic turnover. The ubiquinone binding sites Q_i, Q_o together with haems b_L and b_H (b-chain) are embedded in cytochrome b subunit (light orange rectangle). The Rieske protein (light magenta) harbouring 2Fe–2S (FeS) iron–sulfur cluster and cytochrome c₁ subunit (dark orange) with haem c₁ transfer the electrons from Q_o site to cytochrome c (red). The proton uptake and release is indicated by red arrows. The intermonomer electron transfer at the level of two haems b_L [5,6] is indicated by dashed arrow. For clarity, the second monomer is shown in grey. Ubiquinone (UQ) and ubiquinol (UQH₂) constitute the Q pool.