Qo site of the bc1 complex; unlocking the gate of the electron transport chain
type: CreativeWork
description: The bc1 complex of the electron transport chain is critical to production of ATP through the proton gradient driven by quinone oxidation; a ubiquitous mechanism for energy conversion throughout the biosphere. In addition to being a central source of energy transduction, its bypass reactions can also lead to production toxic ROS formation from semiquinone intermediates. Its internal proton/electron shuttling and gating mechanisms have been a source of controversy and debate for decades. Structural and kinetic analysis of the bc1 complex suggests several proton-coupled electron transfer processes in which gating mechanisms favor rapid forward flux while minimizing deleterious by-pass reactions. Most important are those involved in the bifurcated reaction at the Qo site. The first electron transfer normally determines the overall rate. However, control of the fate of the intermediate semiquinone involves the second step. Interplay between charged intermediates arising from the separation of proton and electron transfer pathways, and involving conserved glutamate-295 (E295), allow coulombic control, while rotation of the E295 sidechain opens a volume into which the semiquinone can diffuse towards the electron acceptor, heme bL in the low potential chain, so as to facilitate its oxidation. When E295 is mutated, these processes are so strongly perturbed that the second electron transfer becomes the rate-limiting step, as demonstrated by measurement of flash-activated kinetics of the bc1 in chromatophores from wild type and E295 mutant strains of Rhodobacter sphaeroides, which show strong inhibi-tion of QH2 oxidation, and a dramatic difference in pH-dependence of activity. Attention has more recently been focused on the intermediate semiquinone, detected in the ~10-50 ms range using rapid-mix freeze-quench approaches, and shown to accumulate to low-occupancy under conditions in which its oxidation is inhibited. In our ~50ms freeze quenched studies, we showed that accumulat…
abstract: The bc1 complex of the electron transport chain is critical to production of ATP through the proton gradient driven by quinone oxidation; a ubiquitous mechanism for energy conversion throughout the biosphere. In addition to being a central source of energy transduction, its bypass reactions can also lead to production toxic ROS formation from semiquinone intermediates. Its internal proton/electron shuttling and gating mechanisms have been a source of controversy and debate for decades. Structural and kinetic analysis of the bc1 complex suggests several proton-coupled electron transfer processes in which gating mechanisms favor rapid forward flux while minimizing deleterious by-pass reactions. Most important are those involved in the bifurcated reaction at the Qo site. The first electron transfer normally determines the overall rate. However, control of the fate of the intermediate semiquinone involves the second step. Interplay between charged intermediates arising from the separation of proton and electron transfer pathways, and involving conserved glutamate-295 (E295), allow coulombic control, while rotation of the E295 sidechain opens a volume into which the semiquinone can diffuse towards the electron acceptor, heme bL in the low potential chain, so as to facilitate its oxidation. When E295 is mutated, these processes are so strongly perturbed that the second electron transfer becomes the rate-limiting step, as demonstrated by measurement of flash-activated kinetics of the bc1 in chromatophores from wild type and E295 mutant strains of Rhodobacter sphaeroides, which show strong inhibi-tion of QH2 oxidation, and a dramatic difference in pH-dependence of activity. Attention has more recently been focused on the intermediate semiquinone, detected in the ~10-50 ms range using rapid-mix freeze-quench approaches, and shown to accumulate to low-occupancy under conditions in which its oxidation is inhibited. In our ~50ms freeze quenched studies, we showed that accumulat…
author: Burton, Rodney Lane
language: en
keywords: Q Cycle, Semiquinone, Biophysics, Structural, Electron Paramagnetic Resonance (EPR), Kinetics
date published: 2015-09-29T20:50:07Z
date modified: 2026-07-22T22:26:31Z
provider: University of Illinois - Urbana-Champaign
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: University of Illinois at Urbana-Champaign

PropertyValue
property ID: Handle
value: http://hdl.handle.net/2142/88205