Coenzyme Q

Coenzyme Q (CoQ), also known as ubiquinone or ubiquinol, is a biologically active quinone with an isoprenoid side chain, related in structure to vitamin K and vitamin E.

The oxidized structure of CoQ, or Q, is given here:

The various kinds of Coenzyme Q can be distinguished by the number of isoprenoid side chains they have. The most common CoQ in human mitochondria is Q 10. The image above has three isoprenoid units and would be called Q 3.

If Coenzyme Q is reduced by one equivalent, the following structure results, a ubisemiquinone, and is denoted QH. Note the free radical on one of the ring oxygens.

If Coenzyme Q is reduced by two equivalents, the compound becomes a '''ubiquinol , denoted QH₂''':

CoQ is found in the membrane of the mitochondrion, and is capable of passing reducing equivalents to acceptors such as Coenzyme Q - cytochrome c reductase:

CoQH₂+ 2 Fe⁺³-cytochrome c → CoQ + 2 Fe⁺²-cytochrome c

Because of its ability to transfer electrons and therefore act as an antioxidant, Coenzyme Q has become a fashionable dietary supplement.