FIG. 5.

Free radical scavenging in the lipid compartment. Initiators of lipid peroxidation such as lipid peroxyl radicals (L–OO•) and nitrogen dioxide (•NO₂) are scavenged by α-tocopherol during which an α-tocopherol radical (α-tocopherol•) is formed. The α-tocopherol radical is subsequently reduced by ascorbic acid (asc. acid) or ubiquinol (UQH₂, depicted on the left), resulting in the formation of an ascorbic acid (asc. acid•) or ubisemiquinone radical (UQH•), respectively. Alternatively, UQH• is formed during the direct reduction of L–OO• or •NO₂ by UQH₂ (depicted on the right). UQH• reacts with O₂ to form UQ as well as superoxide anion (O₂^•−). UQ can be regenerated into UQH₂ via reduction by the mitochondrial ETC, but UQH₂ is also synthesized endogenously from acetyl CoA via the MP (upper right corner). In addition, UQ can undergo (auto-)oxidation (ox.) into inactive metabolites (lower right corner). MP, mevalonate pathway; UQ/UQH₂, ubiquinone/ubiquinol, also referred to as coenzyme Q10. To see this illustration in color, the reader is referred to the web version of this article at www.liebertpub.com/ars