Hypothesis on the Mechanism of Proton Transport in Biological Membranes

Hypothesis on the Mechanism of Proton Transport in Biological Membranes 

Apart from the protein matrix, where it is possible for protons to move effectively in keeping with a mechanism somewhat similar to that proposed for the motion of protons in ice there is another path for protons through hydrophobic barrier of which the membrane is an example. This transition is based on the observations of phase transitions in a bilayer by X-ray diffraction methods. In this mechanism developed for mitochondria the main role falls to cardiolipin, which accounts for 33% of the total amount of lipids in the mitochondrial membrane.146 The protonation of the head groups of cardiolipin contained in the membranes of mitochondria caused a phase transition of the bilayer into an inverted hexagonal phase.147 This process is promoted by calcium ions whose reactions with the head groups of lipids favor neutralization of the membrane charge and effective dehydration of the polar heads. 

Investigation of intact mitochondria, conducted by the 31P-NMR method, indicate that 95% of the membranes are organized in the form of bilayers. Consequently, nonbilayer structures, which are less of a barrier to proton transport, if they exist at all, are fairly rare, or extremely unstable states.148 

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