Jan 15, 2014

Proton pumping in cytochrome c oxidase: energetic requirements and the role of two proton channels

Biochimica Et Biophysica Acta
Margareta R A Blomberg, Per E M Siegbahn

Abstract

Cytochrome c oxidase is a superfamily of membrane bound enzymes catalyzing the exergonic reduction of molecular oxygen to water, producing an electrochemical gradient across the membrane. The gradient is formed both by the electrogenic chemistry, taking electrons and protons from opposite sides of the membrane, and by proton pumping across the entire membrane. In the most efficient subfamily, the A-family of oxidases, one proton is pumped in each reduction step, which is surprising considering the fact that two of the reduction steps most likely are only weakly exergonic. Based on a combination of quantum chemical calculations and experimental information, it is here shown that from both a thermodynamic and a kinetic point of view, it should be possible to pump one proton per electron also with such an uneven distribution of the free energy release over the reduction steps, at least up to half the maximum gradient. A previously suggested pumping mechanism is developed further to suggest a reason for the use of two proton transfer channels in the A-family. Since the rate of proton transfer to the binuclear center through the D-channel is redox dependent, it might become too slow for the steps with low exergonicity. Therefore, a ...Continue Reading

Mentioned in this Paper

Thermodynamics
Biochemical Pathway
Cytochrome C Oxidase
Cytochrome c Oxidase Subunit VIa
Bacterial Proteins
Histidine
Enzymes, antithrombotic
Extravasation
Plain X-ray
Oxidase

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