ABSTRACT
Intracellular reductants participate in regulation of oxidative stress through their direct interactions with chain-initiating and/or chain-propagating free radicals and via reduction (enzymatic or nonenzymatic) of molecular products formed from reactive oxygen species or peroxyl radicals, i.e., hydroperoxides. The major protective antioxidant reaction is:
(8.1)
in which reductants (AH) act as donors of hydrogen for peroxyl radicals (scavengers) to form relatively stable molecular products (hydroperoxides) from reactive chain-propagating radical species at the expense of antioxidant radical (A•) production. An effective biological antioxidant is the one that: (i) effectively scavenges peroxyl radicals, and (ii) whose radicals are not reactive enough to attack important biomolecules. In biomembranes, vitamin E is a good example of an effective antioxidant whose topography in membrane provides not only for effective reaction with polar peroxyl radicals, but is also optimized for important interactions with other reducing antioxidants (such as ascorbate) to completely prevent potential interactions of vitamin E radicals with membrane constituents.
