Antioxidants such as ascorbate and glutathione serve to inactivate radicals and counteract spontaneous oxidation reactions, such as unwanted disulfide bonds in proteins. These systems are cycles, where a "spent" antioxidant (say, oxidized glutathione) is convert back to its reduced form by another reducing agent, usally NADPH.
My question is, how much NADPH (or reducing equivalents) does a cell devote to this antioxidant defense? What is the flux, in molar amounts per unit time, through these systems? Does it represent a large portion of the energy metabolism of cells?
I am guessing that the flux is quite large, but I have never seen any data on this. Most likely it varies a lot between cell types, but I would be happy to see any numbers. I think this is important for understanding antioxidant chemistry in cells, yet it is rarely discussed in the literature.