Figure 16-19. The pathway of electron transport (blue arrows) and proton transport (red arrows) in the inner mitochondrial membrane.

Figure 16-19The pathway of electron transport (blue arrows) and proton transport (red arrows) in the inner mitochondrial membrane

Bound to each of the electron transport complexes are several prosthetic groups, which carry electrons through the complex. (Top) A pair of electrons from one NADH first move through the NADH-CoQ reductase complex to one coenzyme Q (CoQ) molecule, which binds reversibly to the complex. The reduced CoH2 diffuses in the membrane and donates electrons to the CoQH2 – Cyt c reductase complex. The peripheral protein cytochrome c diffuses in the intermembrane space, transporting electrons (one at a time) from the CoQH2 – Cyt c reductase complex to the cytochrome c oxidase complex and ultimately to O2. Protons are pumped from the matrix into the intermembrane space at the indicated sites. The protons released into the matrix space by the oxidation of NADH are consumed in the formation of water from O2, resulting in no net proton translocation from these reactions. Thus a total of 10 protons are translocated per pair of electrons moved from NADH to O2. (Bottom) The succinate-CoQ reductase complex oxidizes succinate to fumarate, reducing one CoQ to CoQH2. No protons are translocated by the succinate-CoQ reductase complex. The remainder of electron transport from succinate proceeds by the same path as in the top diagram. Thus for every pair of electrons transported from succinate to O2, six protons are translocated from the matrix into the intermembrane space.

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From: Section 16.2, Electron Transport and Oxidative Phosphorylation

Cover of Molecular Cell Biology
Molecular Cell Biology. 4th edition.
Lodish H, Berk A, Zipursky SL, et al.
New York: W. H. Freeman; 2000.
Copyright © 2000, W. H. Freeman and Company.

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