The Mitochondrial Free Radical Theory of Aging - Supernova: Pliki

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The Mitochondrial Free Radical Theory of Aging
Fig. 11.8. Routes of proton and hydroxide flow incorporating the phosphate carrier.
antiport with hydroxide. 53,54 The relevance of this is that the permeability of the inner membrane
to water 55 renders hydroxide transport functionally equivalent to reverse proton transport,
so that if the phosphate carrier were trapping hydroxide ions in the matrix and releasing
them in the cytosol at some distance from the membrane—perhaps a nanometer or so
further away from it than the distance at which the respiratory chain and ATPase were
trapping and releasing protons—then the inevitable (see Section 11.3.6) steady-state current
in the aqueous medium, perpendicular to the membrane, would be sustained indefinitely
(Fig. 11.8). It is plausible that hydroxide trapping and release should indeed occur some
way from the membrane, because they are in more plentiful supply there (on account of
the pH gradient, Fig. 11.2) so the carrier can achieve faster turnover. Another circumstantial
point in favour of this idea is that the one energy-transducing biological system which is
not associated with hydroxide transport, namely the thylakoid of chloroplasts, does make
a sufficient ΔpH (bulk-to-bulk) to drive ATP synthesis unaided. A third one is the coordinate
loss of inner membrane cardiolipin and OXPHOS performance with age: cardiolipin is the
only charged phospholipid present in significant amounts in that membrane (see Section 4.1),
so cardiolipin depletion reduces the organisation of surface water and allows more protons