A ubiquinol is an electron-rich (reduced) form of coenzyme Q (ubiquinone). The term most often refers to ubiquinol-10, with a 10-unit tail most commonly found in humans. The natural ubiquinol form of coenzyme Q is 2,3-dimethoxy-5-methyl-6-poly prenyl-1,4-benzoquinol, where the polyprenylated side-chain is 9-10 units long in mammals. Coenzyme Q₁₀ (CoQ₁₀) exists in three

redox Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...

states, fully

oxidized Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...

(

ubiquinone Coenzyme Q, also known as ubiquinone and marketed as CoQ10, is a coenzyme family that is ubiquitous in animals and most bacteria (hence the name ubiquinone). In humans, the most common form is coenzyme Q10 or ubiquinone-10. It is a 1,4-benzoq ...

), partially reduced ( semiquinone or ubisemiquinone), and fully reduced (ubiquinol). The redox functions of ubiquinol in cellular energy production and antioxidant protection are based on the ability to exchange two

electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no ...

s in a redox cycle between ubiquinol (reduced) and the ubiquinone (oxidized) form.

Characteristics

Because humans can synthesize ubiquinol, it is not classed as a

vitamin A vitamin is an organic molecule (or a set of molecules closely related chemically, i.e. vitamers) that is an essential micronutrient that an organism needs in small quantities for the proper functioning of its metabolism. Essential nutrie ...

Bioavailability

It is well-established that CoQ₁₀ is not well absorbed into the body, as has been published in many peer-reviewed scientific journals. Since the ubiquinol form has two additional hydrogens, it results in the conversion of two ketone groups into hydroxyl groups on the active portion of the molecule. This causes an increase in the polarity of the CoQ₁₀ molecule and may be a significant factor behind the observed enhanced bioavailability of ubiquinol.

Content in foods

In foods, there are varying amounts of ubiquinol. An analysis of a range of foods found ubiquinol to be present in 66 out of 70 items and accounted for 46% of the total coenzyme Q10 intake (in the Japanese diet). The following chart is a sample of the results.

Molecular aspects

Ubiquinol is a benzoquinol and is the reduced product of

also called coenzyme Q₁₀. Its tail consists of 10 isoprene units.

The reduction of ubiquinone to ubiquinol occurs in Complexes I & II in the

electron transfer chain An electron transport chain (ETC) is a series of protein complexes and other molecules that transfer electrons from electron donors to electron acceptors via redox reactions (both reduction and oxidation occurring simultaneously) and couples thi ...

. The Q cycle is a process that occurs in

cytochrome b Cytochrome b within both molecular and cell biology, is a protein found in the mitochondria of eukaryotic cells. It functions as part of the electron transport chain and is the main subunit of transmembrane cytochrome bc1 and b6f complexes. F ...

, a component of Complex III in the electron transport chain, and that converts ubiquinol to ubiquinone in a cyclic fashion. When ubiquinol binds to cytochrome b, the pKa of the phenolic group decreases so that the proton ionizes and the phenoxide anion is formed. Ubiquinol semiphenoxide

If the phenoxide oxygen is oxidized, the semiquinone is formed with the unpaired electron being located on the ring. Ubiquinol semiquinone

References

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