ubiquinone

Ubiquinone, more commonly known as coenzyme Q (CoQ), is a lipophilic benzoquinone molecule that serves as an essential electron carrier in cellular respiration. In humans, the predominant form is ubiquinone-10 (CoQ10), named for its ten isoprenoid units in the hydrophobic tail that anchors the molecule within lipid membranes.

In mitochondria, ubiquinone shuttles electrons from Complex I (and, for certain substrates, Complex II) to Complex III of the electron transport chain, contributing to the proton gradient that drives ATP synthesis. The molecule cycles between an oxidized form (ubiquinone) and a reduced form (ubiquinol) as it accepts and donates electrons.

Biosynthesis and distribution: CoQ is synthesized endogenously in cells, with the isoprenoid tail derived from cellular pathways that supply the tail length appropriate to the organism (CoQ10 in humans). While humans produce sufficient amounts, production tends to decline with age, and dietary intake provides supplementary CoQ.

Functions beyond electron transport: In addition to its role in respiration, ubiquinone acts as a lipid-soluble antioxidant, protecting membranes from lipid peroxidation by scavenging reactive oxygen species. It may participate in redox signaling and influence the activity of certain enzymes.

Dietary sources and clinical relevance: CoQ is found in meat, fish, and some vegetables. In medicine, CoQ10 supplementation is used for certain mitochondrial disorders and to mitigate statin-associated myopathy in some cases, though evidence varies. It is generally well tolerated, but high doses can cause gastrointestinal symptoms and may interact with anticoagulants.