White matter comprises over half of the brain, and its role in axonal survival is being reconsidered, consistently with the observation that axonal degeneration follows demyelization. The recent evidence of an extra-mitochondrial aerobic ATP production in isolated myelin vesicles, thanks to the expression therein of the mitochondrial Oxydative Phosphorylation (OXPHOS) machinery, stands in for myelin playing a functional bioenergetic role in ATP supply for the axon. The observation that subunits of the OXPHOS encoded by the mitochondrial genome are expressed in myelin, suggests that they can be the same as those of the inner mitochondrial membrane. This would mean that the OXPHOS is exportable. Here the hypothesis is exposed that the mitochondrion is the unique site of the assembly of the OXPHOS, so that this is exported to those sub cellular districts displaying high energy demand, such as myelin sheath. There the OXPHOS would display a higher efficiency in oxidative ATP production than inside the mitochondrion itself. In this respect, the role of the glia in the nervous conduction is shed new light and the oligodendrocyte mitochondrial OXPHOS are hypothesized to be delivered to nascent myelin.
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