Free radical Reactions in the Catalytic Cycle of Cytochrome bc Complexes
EMSL Project ID
19832
Abstract
The cytochrome bc complex is a large ~750 kiloDalton molecular weight protein complex that is embedded in the mitochondrial or cellular membrane and is a central component of the electron transport chain of humans, plants, all higher organisms and a wide variety of disease-causing micro-organisms. The function of the bc complex is to oxidize quinol and convert its electron or redox energy into chemical energy by pumping protons across the membrane. The proton transport establishes a proton gradient that drives the synthesis of ATP. The bc complex is highly efficient in this conversion of redox to chemical energy and makes a decisive contribution to the overall energetics of the organism, normally without the production of any toxic products.This project focuses on the least understood step in the catalytic cycle of the bc complex: the oxidation of the quinol by removal of two electrons and two protons. We address two major issues: 1) How the two electrons from each quinol are separated by the protein and sent down two different electron transport chains in three different metalloprotein subunits of the bc complex; and 2) How several side reactions that waste energy and create toxic by-products such as superoxide are strongly suppressed even though they are thermodynamically more favorable than the proton pumping reaction. These questions will be addressed by an integrated program of pulsed EPR and ENDOR measurements on the recently discovered semiquinone intermediate in the bc complex, combined with state of the art computational modeling of the semiquinone and its possible interactions with the protein.
We seek to understand how this protein complex converts the flow of electrons to chemical energy is a safe and highly efficient manner in a living cell. The results will provide a blueprint for the interconversion of electron flow and chemical energy in fuel cells, photovoltaic and solar energy conversion devices. This work will also reveal key details in a membrane-embedded, metalloprotein complex fundamental to life as we know it and support the mission of EMSL to provide scientific and technological needs of DOE and the nation.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2006-08-08
End Date
2008-12-02
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
A semiquinone intermediate generated at the Qo site of the cytochrome bc1 complex: Importance for the Q-cycle and superoxide production