Cellular respiration - ubiquinone

Ubiquinone, also known as coenzyme Q, coenzyme Q10, ubidecarenone, Q or Q10 is a hydrophobic 1,4-benzoquinone that belongs to the class of isoprenoid compounds (the number 10 in Q10 represents the number of isoprene units in its tail). It was first discovered in 1957 and a year later its chemical structure was described.

It has antioxidant properties, that means, it has the ability to act in oxidation-reduction reactions. In fact, its oxidized form may accept two electrons, passing to the reduced form, ubiquinol (sometimes represented as QH2). It may also be in an intermediate state (ubisemiquinone). This redox ability makes it useful in eliminating free radicals, as well as in electron transfer processes. And this is exactly its main function in our body: it is one of the components of the mitochondrial respiratory chain. Although not being part of any complex of the chain, it plays a key role in the process, because it accepts electrons from the complex I or complex II and delivers them to complex III. To exert this function, ubiquinone takes advantage of its high membrane diffusivity, which allows it to diffuse easily across the mitochondrial inner membrane, a consequence of its small size and hydrophobic character. Ubiquinone is present in most eukaryotic cells, specifically in the inner mitochondrial membrane. Nevertheless, it is also found in lesser amounts in the membrane of several other organelles such as peroxisomes, endoplasmatic reticulum and lysosomes.

The synthesis of ubiquinone shares several steps with the synthesis of cholesterol, namely until the production of mevalonate. Globally, it is a complex process, which uses at least 12 enzymes, and occurs in mitochondria, endoplasmic reticulum and peroxisomes. The synthesis of ubiquinone involves the HMG-CoA reductase enzyme, which is the main pharmacological target of statins (drugs used in individuals with an excess of cholesterol in the body, through the inhibition of the synthesis of the lipid). Consequently, one of the side effects of its adminis of statins may be a decrease in ubiquinone production.