Electron Transport Chain, part 4: Oxidative Phosphorylation (pH + ATP-synthase)
Author: Milada Teplá, Faculty of Science, Charles University, www.studiumbiochemie.cz
Electron transport causes Complexes I, III and IV to transport protons across the inner mitochondrial membrane from matrix to the intermembrane space. An electrochemical gradient across the inner mitochondrial membrane is created. [H+] in intermembrane space is higher than [H+] in matrix (pH(out) is less than pH(in)). Matrix is a region of low [H+] and negative electrical potential. Intermembrane space is a region of high [H+] and positive electrical potential. The free energy sequestered by the resulting electrochemical gradient (proton-motive force) powers ATP synthesis.
The synthesis of Adenosine triphosphate (ATP) from Adenosine diphosphate (ADP) and inorganic phosphate (Pi) in mitochondrion is the endergonic process. The synthesis of ATP is catalyzed by proton-translocating ATP synthase and is driven by the electron-transport process. The electrochemical potential of H+ gradient across the inner mitochondrial membrane is harnessed to synthesize ATP. The synthesis of one ATP molecule seems to require the translocation of about three protons. This synthesis of ATP is called oxidative phosphorylation.