In cell membranes, vitamin E is oxidized by free radicals. This is reduced by CoQ10, which itself is regenerated by the respiratory chain, to the degree that respiration is not “impaired.”
Or: diffusible vitamin C, or more optimally vitamin C held near the membrane by something (possibly including vitamin E), reduces vitamin E, glutathione reduces vitamin C, glutathione reductase reduces oxidized glutathione, and ultimately NADPH is regenerated by the oxidation of foodstuffs (pentose phosphate pathway oxidative cycle in which two glucose-6-phosphate are oxidized twice to produce four NADPH, two carbon dioxides, and two ribulose-5-P, which are non-oxidatively recycled back to one four carbon sugar plus one glucose-6-P, using transketolase, transaldolase, and phosphoglucose isomerase; in this way NADPH can be ramped up to appropriate levels for reduction of oxidized glutathione, keeping the antioxidant network [as noted above, involving minimally vitamin E, vitamin C, glutathione, glutathione reductase, and NADPH from the pentose phosphate pathway, but likely many more participants, including antioxidant enzymes and other small molecule antioxidants.] running smoothly, and reductive biosynthesis. When NADPH is sufficiently high, ribulose-5-phosphate can be used to make ribose-5-phosphate and its derivatives). NADPH is the ultimate or ground zero antioxidant in the body. NADH and FADH2, also regenerated from the oxidation of foodstuffs, serve as additional reservoirs of reducing power in the cell.
The above description is that of a relay shuttle, which carries away harmful molecules from the site where they would otherwise do the most damage.
The body uses the network principle, not the pharmaceutical principle, and thus achieves higher signal/noise ratios. The highest signal/noise ratio is never seen in any natural process near the maximum signal, as the pharmaceutical model presupposes. Rather the highest overall signal/noise ratio is achieved using concentrations of each component of a large network well off their maximal effective dose.
A shuttle network makes it obvious why it is not useful to overdose on any one component of the network. Optimal -not maximal- doses of ALL components (including the cofactors in the antioxidant enzymes) and precursors (in the case of making the enzymes and glutathione) make more sense in supplements.