Figure 8.

(A and B) Assumed dimer of the H. modesticaldum cytochrome bc complex: blue for the cytochrome b subunit, purple for the Fe–S subunit, and green for the cytochrome f subunit. (A) Imagined left half of dimer shown as homology-modeled subunits of the H. modesticaldum cytochrome bc complex. (B) Right side of the dimer shown as the determined crystal structure of the cytochrome bc₁ complex from Rhodobacter sphaeroides used as the template for Figure 8A. Heme cofactors are colored red. (C) Proposed H. modesticaldum cytochrome bc complex bifurcated electron-transfer steps and mechanism: Q for quinones, Q_o for the quinone oxidation site, Q_i for the quinone reduction site, R for Rieske Fe–S, b_L,H for b-type hemes, H_1,2 for DHCC c-type hemes, and c₅₅₃ for electron acceptor soluble cytochrome c₅₅₃.