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(also benzoquinone, coenzyme Q), any of a series of derivatives of 5-methyl-2,3-dimethoxyquinone having a variable terpenoid side chain attached to the carbon atom in position six. Ubiquinones have from six to ten isoprenoid units (C5H8). The structural formula is

Ubiquinones figure in reactions that supply energy to cells. They are designated by the symbols UQn or CoQn; in the first, n represents the number of carbon atoms, and in the second, the number of isoprenoid units. For example, UQ30 will correspond to CoQ6. Ubiquinones occur as colorless, crystalline substances whose absorption maximum is at 270 micrometers. They are insoluble in water and soluble in organic solvents.

Ubiquinones are present in all organisms; UQ50 predominates in mammals, UQ30–50 in fungi, UQ40 in bacteria, UQ40–45 in protozoa, and UQ45–50 in insects. Plant mitochondria contain UQ40–50 in small quantities, and the chloroplasts in plants contain plastoquinones, which are similar to ubiquinones. Various naph-thoquinones occur in certain bacteria.

The biological role of ubiquinones is based on their ability to participate in reversible oxidation-reduction conversions. Ubiquinones are located in the cytoplasmic membranes of bacteria and in the inner membranes of mitochondria. They participate in the transfer of electrons and hydrogen between flavoproteins and cytochrome b in the respiratory chain.


Skulachev, V. P. Transformatsiia energii v biomembranakh. Moscow, 1972.
Morton, R. A. “Ubiquinones, Plastoquinones, and Vitamins K.” Biological Reviews of the Cambridge Philosophical Society, 1971, vol. 46, no. 1.


References in periodicals archive ?
A mitochondrial-targeted ubiquinone modulates muscle lipid profile and improves mitochondrial respiration in obesogenic diet-fed rats.
Caption: Figure 2: Mitochondria-targeted antioxidants with ubiquinone or plastoquinone antioxidant moiety, that are used in kidney ischemia/reperfusion injury.
Drug Antioxidant moiety Reference MitoQ Ubiquinone [72] SkQ1, SkQR1 Plastoquinone [74-76] SS-31 (Bendavia) Tyr or Dmt (2',6'- [106,107] dimethyltyrosine) residues SOD mimic (i) MnTMPyP Manganese metalloporphyrin (ii) MnTnHex- 2-Py[P.
In tissues, CoQ10 exists as oxidized ubiquinone and reduced ubiquinol.
The kinetics of the redox reactions of ubiquinone related to the electron-transport activity in the respiratory chain.
The endogenous ubiquinones play a key role in one-electron transfers in the mitochondrial inner membrane as well as PTP transition (Fontaine et al.
should be shifted to the left in case of ubiquinone and to the right in case of plastoquinone, in agreement with our observations and also the earlier reports on the long life of pulse-generated ubiquinone radicals in the presence of oxygen [117, 119].
10]), the predominant ubiquinone species in humans, functions as an electron carrier in the mitochondrial electron transport chain (ETC) and as an intracellular antioxidant (1).
Determination of reduced and total ubiquinones in biological materials by liquid chromatography with electrochemical detection.
The specificity of mitochondrial complex I for ubiquinones.