Chapter 7: The bc₁ Complex: A Physicochemical Retrospective and an Atomistic Prospective

Although the bc₁ complex is dimeric, the modified Q-cycle explains the behavior in normal forward flux through a monomeric mechanism. However, the need to minimize generation of reactive oxygen species raise questions about complexities associated with control and gating, the role of the dimeric configuration, complex dynamics (the Q_o-site ballet), and involvement of atomistic processes are not readily accessible to direct study. Interactions across the dimer interface, a chemical spring-loaded ratchet, complexation of the intermediate semiquinone by ISPH to reduce reactivity with O₂, and coulombic gating, are reviewed in the context of direct measurements of proton release, and further exploration through computational approaches using molecular dynamics supplemented by quantum chemical calculations to quantify atomistic features, in a new model of the Rhodobacter sphaeroides complex.