On Air

Advertising

Plastoquinone

|Section2={{Chembox Properties | C=53 | H=80 | O=2 | Appearance = | Density = | MeltingPt = | BoilingPt = | Solubility = }} |Section7={{Chembox Hazards | MainHazards = | FlashPt = | AutoignitionPt = }} |Section8={{Chembox Related | OtherCompounds = 1,4-benzoquinone quinone Coenzyme Q10 }} }} Plastoquinone (PQ) is a isoprenoid quinone molecule involved in the electron transport chain in the light-dependent reactions of photosynthesis. Structurally, it is usually a 2,3-dimethyl-1,4- benzoquinone molecule with a side chain of nine isoprenyl units. This is the most common form of plastoquinone, known as PQ-A or PQ-9. There are other forms of plastoquinone, such as ones with shorter side chains like PQ-3, as well as analogs such as PQ-B, PQ-C, and PQ-D. The benzoquinone and isoprenyl units are both hydrophobic, enabling this molecule to be dissolved within the inner section of a lipid bilayer, where the hydrophobic tails are usually found. It is very structurally similar to ubiquinone, or Coenzyme Q10, differing by the length of the isoprenyl side chain, replacement of the methoxy groups with methyl groups, and removal of the methyl group in the 2 position on the quinone. Like ubiquinone, it can come in several redox states, plastoquinone, plastosemiquinone (unstable), and plastoquinol (PQH2), which differs from plastoquinone by having two hydroxyl groups instead of two carbonyl groups. Plastoquinol, the reduced form, also functions as an antioxidant by reducing reactive oxygen species, some produced from the photosynthetic reactions, that could harm the cell membrane. The prefix plasto- means either plastid or chloroplast, alluding to its location within the cell.http://dictionary.reference.com/browse/Plastoquinone Definition of plastoquinone

Role in Photosynthesis

Plastoquinone is reduced when it accepts two electrons from photosystem II and two hydrogen cations (H+) from the stroma of the chloroplast, thereby forming plastoquinol (PQH2). It transfers the electrons further down the electron transport chain to plastocynanin through the cytochrome b6f protein complex, which, besides catalyzing the electron transfer, also transports the two protons into the lumen of thylakoid discs. It is found within photosystem II in two specific binding sites, known as QA and QB. The plastoquinone at QA, the primary binding site, is very tightly bound, compared to the plastoquinone at QB, the secondary binding site, which is much more easily removed. QA is only transferred a single electron, so it has to transfer an electron to QB twice before QB is able to pick up two protons from the stroma and be replaced by another plastoquinone molecule. The protonated QB then joins a pool of free plastoquinone molecules. There are additional plastoquinone binding sites (QC and possibly QD), but their existence and function have not been fully elucidated.

Derivatives

Some derivatives designed to penetrate cell membranes ( SkQ1 (plastoquinonyl-decyl-triphenylphosphonium), SkQR1 (the rhodamine-containing analog of SkQ1), SkQ3) have anti-oxidant and protonophore activity. SkQ1 has been proposed as an anti-aging treatment, with the possible reduction of age-related vision issues due to its antioxidant ability.http://protein.bio.msu.ru/biokhimiya/contents/v73/pdf/bcm_1329.pdf Mitochondria-Targeted Plastoquinone Derivatives as Tools to Interrupt Execution of the Aging Program. 5. SkQ1 Prolongs Lifespan and Prevents Development of Traits of Senescence. Anisimov etal. 2008 This antioxidant ability results from both its ability to reduce reactive oxygen species (derived from the part of the molecule containing plastoquinone), which are often formed within mitochondria, as well as its ability in increase ion exchange across membranes (derived from the part of the molecule containing cations that can dissolve within membranes). SkQR1 has also been proposed as a possible way to treat brain issues like Alzheimer's due to its ability to potentially fix damages caused by amyloid beta. SkQ1 is starting clinical trials for glaucoma in Russia.

References

External links

"green air" © 2007 - Ingo Malchow, Webdesign Neustrelitz
This article based upon the http://en.wikipedia.org/wiki/Plastoquinone, the free encyclopaedia Wikipedia and is licensed under the GNU Free Documentation License.
Further informations available on the list of authors and history: http://en.wikipedia.org/w/index.php?title=Plastoquinone&action=history
presented by: Ingo Malchow, Mirower Bogen 22, 17235 Neustrelitz, Germany