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A Kinetic model of proton transport in a multi-redox centre protein: cytochrome c oxidase

Posted on 21. February, 2014.

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Cytochrome c Oxidase (CcO) is the final complex of the respiratory chain. Its purpose is to use the energy gained by the reduction of oxygen to water to pump protons against a difference of electrochemical potentials across the mitochondrial inner membrane. 

This pumping is achieved by coupling a number of electron (ET) and proton transfer (PT) steps. The stepwise transfer is under debate since CcO has been recognised as a proton pump for more than three decades. According to current view, the gradual increase of the pK value during each ET step leads to the transfer of a proton to the proton loading site (PLS), which is separated from the site where oxygen chemistry occurs. After the transfer of a proton to the PLS, another proton is taken 
up for the chemical reaction in the catalytic site. Electrostatic repulsion from this second proton will then expel the proton out of the PLS. This view is hard to challenge experimentally, particularly since few methods are available to follow ET and HT steps during an entire catalytic cycle. 
A convenient way to study proton-coupled ET is chemical reaction kinetics initiated by electrochemistry. In this study, we make use of a model system developed earlier, which permits direct ET to redox enzymes.

Click here to read the full article in Progress in Reaction Kinetics and Mechanism.


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