Ubiquinol

Ubiquinol
Names
IUPAC name
2-[(2E,6E,10E,14E,18E,22E,26E,30E,34E)-3,7,11,15,19,23,27,31,35,39-decamethyltetraconta-2,6,10,14,18,22,26,30,34,38-decaenyl]-5,6-dimethoxy-3-methyl-benzene-1,4-diol
Other names
Reduced CoQ10, unoxidized CoQ10, CoQ10H2, or dihydroquinone
Identifiers
992-78-9 N
ChemSpider 17216048 N
Jmol 3D image Interactive graph
MeSH C003741
PubChem 9962735
Properties
C59H92O4
Molar mass 865.38 g·mol−1
Appearance off-white powder
Melting point 45.6 °C (114.1 °F; 318.8 K)
practically insoluble in water
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YesYN ?)
Infobox references
Not to be confused with Ubiquitin.

Ubiquinol is an electron-rich (reduced) form of coenzyme Q10.

The natural ubiquinol form of coenzyme Q10 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 states, fully oxidized (ubiquinone), 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 electrons in a redox cycle between ubiquinol (reduced) and the ubiquinone (oxidized) form.[1][2]

Characteristics


Because humans can synthesize ubiquinol, it is not classed as a vitamin.[3]

Bioavailability

It is well-established that CoQ10 is not well absorbed into the body, as has been published in many peer-reviewed scientific journals.[4] 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. Taken orally, ubiquinol exhibits greater bioavailability than ubiquinone.[5]

However, there are authorities that dispute whether ubiquinol is more bioavailable in practice rather than in theory compared to CoQ10 supplements because those have their CoQ10 molecules dissolved in lipid micelles, which then deliver their cargo to the plasma membrane in the intestinal wall. There they dissolve via simple diffusion in the intestinal cells, then onto the lymphatic vessels, and then into the venous system. Since ubiquinol and CoQ10 are redox pairs and can and are rapidly inter-converted in the body, it is not clear that ubiqinol's more hydrophilic nature compared to CoQ10 is of practical significance.[6]

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.[7]

Food Ubiquinol (μg/g) Ubiquinone (μg/g)
Beef (shoulder) 5.36 25
Beef (liver) 40.1 0.4
Pork (shoulder) 25.4 19.6
Pork (thigh) 2.63 11.2
Chicken (breast) 13.8 3.24
Mackerel 0.52 10.1
Tuna (canned) 14.6 0.29
Yellowtail 20.9 12.5
Broccoli 3.83 3.17
Parsley 5.91 1.57
Orange 0.88 0.14

Molecular aspects

Ubiquinol is a benzoquinol and is the reduced product of ubiquinone 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. The Q cycle[8] is a process that occurs in cytochrome b,[9][10] 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.

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

A page on Proteopedia, Complex III of Electron Transport Chain,[11] contains rotatable 3-D structures of Complex III, which may be used to study the peptide structures of Complex III and the mechanism of the Q cycle.

References

  1. ↑ Mellors, A; Tappel, AL (1966). "The inhibition of mitochondrial peroxidation by ubiquinone and ubiquinol". The Journal of Biological Chemistry 241 (19): 4353–6. PMID 5922959.
  2. ↑ Mellors, A.; Tappel, A. L. (1966). "Quinones and quinols as inhibitors of lipid peroxidation". Lipids 1 (4): 282–4. doi:10.1007/BF02531617. PMID 17805631.
  3. ↑ Banerjee R (2007). Redox Biochemistry. John Wiley & Sons. p. 35. ISBN 978-0-470-17732-7.
  4. ↑ James, Andrew M.; Cochemé, Helena M.; Smith, Robin A. J.; Murphy, Michael P. (2005). "Interactions of Mitochondria-targeted and Untargeted Ubiquinones with the Mitochondrial Respiratory Chain and Reactive Oxygen Species: Implications for the use of exogenous ubiquinones as therapies and experimental tools". Journal of Biological Chemistry 280 (22): 21295–312. doi:10.1074/jbc.M501527200. PMID 15788391.
  5. ↑ Hosoe, Kazunori; Kitano, Mitsuaki; Kishida, Hideyuki; Kubo, Hiroshi; Fujii, Kenji; Kitahara, Mikio (2007). "Study on safety and bioavailability of ubiquinol (Kaneka QH™) after single and 4-week multiple oral administration to healthy volunteers". Regulatory Toxicology and Pharmacology 47 (1): 19–28. doi:10.1016/j.yrtph.2006.07.001. PMID 16919858.
  6. ↑ Judy, William. "Coenzyme Q10 Facts or Fiction" (PDF). Thorne Research. Archived from the original (PDF) on August 10, 2013. Retrieved 9 December 2013.
  7. ↑ Kubo, Hiroshi; Fujii, Kenji; Kawabe, Taizo; Matsumoto, Shuka; Kishida, Hideyuki; Hosoe, Kazunori (2008). "Food content of ubiquinol-10 and ubiquinone-10 in the Japanese diet". Journal of Food Composition and Analysis 21 (3): 199–210. doi:10.1016/j.jfca.2007.10.003.
  8. ↑ Slater, E.C. (1983). "The Q cycle, an ubiquitous mechanism of electron transfer". Trends in Biochemical Sciences 8 (7): 239–42. doi:10.1016/0968-0004(83)90348-1.
  9. ↑ Trumpower BL (June 1990). "Cytochrome bc1 complexes of microorganisms". Microbiol. Rev. 54 (2): 101–29. PMC 372766. PMID 2163487.
  10. ↑ Trumpower, Bernard L. (1990). "The Protonmotive Q Cycle". The Journal of Biological Chemistry 265 (20): 11409–12. PMID 2164001.
  11. ↑ http://proteopedia.org/wiki/index.php/Complex_III_of_Electron_Transport_Chain[][]

External links

This article is issued from Wikipedia - version of the Saturday, March 19, 2016. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.