Funding may be available for UK/EU students. If funding is awarded for this project it will cover tuition fees and stipend for UK students. EU students may be eligible for full funding, or tuition fees only, depending on the funding source. International students will not be eligible for this funding however they are still welcome to apply for this project but would have to find alternative funding.
A single family of enzymes, the heme copper oxidases (HCOs) is responsible for >75% of the annual global respiratory consumption of dioxygen. Dioxygen chemistry is closely correlated with proton pumping in this class of enzymes which ultimately drives ATP synthesis. The exact nature of the proton pump driven redox events, however, is not defined since intermediates in the dioxygen chemistry reaction (termed O, R, P and F) are difficult to observe. The aim of the project is to: (A) Identify and locate local and global structural movements associated with the transitions between these O, R, P, F oxidations levels (and their substates). The motions associated with proton-pumping action will be probed using state-of-the-art pulsed EPR methods. As we have already demonstrated, the distance between two spin-labels within an oxidase can be determined using PELDOR methods. Changes in the distance between two spin-labels in response to cycling through the O-R-P-F states will be sought for strategically chosen pairs. The motion of single spin-labels relative to the paramagnetic ions of the active site will similarly be determined. (B) Determine the distribution of electrons within the active site throughout the catalytic cycle. Define the spin and oxidation state of the active site metal ions and the strength of interactions with amino-acid based radicals at each stage. It is the passage of the HCO active site through the O, R, P, F states that drives the proton-pumping mechanism yet the exact nature of these intermediates is far from clear. For example, the Pm and F states in cytochrome oxidase are both assumed to contain an active site heme A chromophore in the Fe(IV)=O state. Yet no explanation exists for the 27 nm difference in the wavelength of the characteristic visible absorption bands of these two forms. Nor is it understood why, in a bo3 oxidase, the optical differences between what are alleged to be the same two forms are negligible. Despite decades of investigation, something apparently simple such as the spin-state of the active-site heme in oxidised cytochrome aa3 is still ambiguous. These questions will be addressed using a combination of EPR spectroscopy and the novel variable-field variable-temperature MCD methods that we developed in order to successfully address the question of the exact nature of the active site in oxidised bo3.
Scholarship Application Deadline: February 4th 2011
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