Mitochondria proton translocation across

In the electron transport chain, CcO receives electrons from cytochrome c, a water-soluble heme protein, on the cytoplasmic side of the membrane, and transfers them through a series of electron transfer steps to the active site, which contains a heme iron and a copper, where the electrons are used to reduce the molecular oxygen. The protons needed for this reaction are taken from the mitochondrion matrix side throngh two proton-conducting channels. In addition to these chemical protons, four more protons, per every oxygen molecule reduced, are translocated across the membrane. The overall enzymatic reaction of CcO is... 

How Many Protons in a Mitochondrion Electron transfer translocates protons from the mitochondrial matrix to the external medium, establishing a pH gradient across the inner membrane (outside more acidic than inside). The tendency of protons to diffuse back into the matrix is the driving force for ATP synthesis by ATP synthase. During oxidative phosphorylation by a suspension of mitochondria in a medium of pH 7.4, the pH of the matrix has been measured as 7.7. 

From a biophysical point of view, the use of whole mitochondrion (or chloroplast) to test the "molecular" theory of Mitchell does not seem satisfying. The translocation of ions, such as protons, across a complex system, such as a cristae, is in itself ill-defined. The interactions between various fluxes (ion and water movements, electron and hole transport, etc.) are far too complex to be amenable to a simple analysis. At the present time, direct tests with the mitochondrial membranes are difficult. Experimental testing of the chemiosmotic hypothesis, using simpler model systems such as planar BLM and spherical liposomes are, therefore, in order. 

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