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Plastoquinone
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<h2 id="role-in-photosynthesis">Role in photosynthesis</h2> <p>The role that plastoquinone plays in photosynthesis, more specifically in the light-dependent reactions of photosynthesis, is that of a mobile electron carrier through the membrane of the <a href="/facts/Thylakoid/d9PEe649">thylakoid</a>.<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> </p><p>Plastoquinone is reduced when it accepts two electrons from <a href="/facts/Photosystem_II/9tmDPU50">photosystem II</a> and two hydrogen cations (H+) from the stroma of the chloroplast, thereby forming plastoquinol (PQH2). It transfers the electrons further down the <a href="/facts/Electron_transport_chain/QjcIkgeR">electron transport chain</a> to <a href="/facts/Plastocyanin/kL1atXsa">plastocyanin</a>, a mobile, water-soluble electron carrier, through the <a href="/facts/Cytochrome_b6f_complex/W1V0MjYM">cytochrome <i>b</i>6<i>f</i></a> protein complex.<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> The cytochrome <i>b</i>6<i>f</i> protein complex catalyzes the electron transfer between plastoquinone and plastocyanin, but also transports the two protons into the lumen of <a href="/facts/Thylakoid/d9PEe649">thylakoid discs</a>.<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a> This proton transfer forms an electrochemical gradient, which is used by <a href="/facts/ATP_synthase/5NBMxsVX">ATP synthase</a> at the end of the light dependent reactions in order to form ATP from ADP and Pi.<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a> </p> <h3>Within photosystem II</h3> <p>Plastoquinone is found within <a href="/facts/Photosystem_II/9tmDPU50">photosystem II</a> 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.<a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a> 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 <a href="/facts/Proton/clCjepXP">protons</a> from the stroma and be replaced by another plastoquinone molecule. The protonated QB then joins a pool of free plastoquinone molecules in the membrane of the thylakoid.<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a><a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a> The free plastoquinone molecules eventually transfer electrons to the water-soluble plastocyanin so as to continue the light-dependent reactions.<a class="footnote-ref" id="fnref:14" href="#fn:14"><sup>14</sup></a> There are additional plastoquinone binding sites within photosystem II (QC and possibly QD), but their function and/or existence have not been fully elucidated.<a class="footnote-ref" id="fnref:15" href="#fn:15"><sup>15</sup></a> </p> <h2 id="biosynthesis">Biosynthesis</h2><p> The p-hydroxyphenylpyruvate is synthesized from <a href="/facts/Tyrosine/RJhEgE4C">tyrosine</a>, while the solanesyl diphosphate is synthesized through the <a href="/facts/Non-mevalonate_pathway/QzMhbrzG">MEP/DOXP pathway</a>. <a href="/facts/Homogentisate/ppChXwVm">Homogentisate</a> is formed from p-hydroxyphenylpyruvate and is then combined with solanesyl diphosphate through a <a href="/facts/Condensation_reaction/wMG0F6La">condensation reaction</a>. The resulting intermediate, 2-methyl-6-solanesyl-1,4-benzoquinol is then <a href="/facts/Methylation/EvDMWVW5">methylated</a> to form the final product, plastoquinol-9.<a class="footnote-ref" id="fnref:16" href="#fn:16"><sup>16</sup></a> This pathway is used in most photosynthetic organisms, like <a href="/facts/Algae/U1ftVKU3">algae</a> and plants.<a class="footnote-ref" id="fnref:17" href="#fn:17"><sup>17</sup></a> However, <a href="/facts/Cyanobacteria/S8bKxIU9">cyanobacteria</a> appear to not use homogentisate for synthesizing plastoquinol, possibly resulting in a pathway different from the one shown below.<a class="footnote-ref" id="fnref:18" href="#fn:18"><sup>18</sup></a></p> <h2 id="derivatives">Derivatives</h2> <p>Some derivatives that were designed to penetrate mitochondrial cell membranes (<a href="/facts/SkQ/tYWo7PLr">SkQ1</a> (plastoquinonyl-decyl-triphenylphosphonium), <a href="/facts/SkQ/tYWo7PLr">SkQR1</a> (the <a href="/facts/Rhodamine/M0IotHXt">rhodamine</a>-containing analog of SkQ1), SkQ3) have <a href="/facts/Anti-oxidant/4TG4MQ83">anti-oxidant</a> and <a href="/facts/Protonophore/VhQzBnuu">protonophore</a> activity.<a class="footnote-ref" id="fnref:19" href="#fn:19"><sup>19</sup></a> SkQ1 has been proposed as an anti-aging treatment, with the possible reduction of age-related vision issues due to its antioxidant ability.<a class="footnote-ref" id="fnref:20" href="#fn:20"><sup>20</sup></a><a class="footnote-ref" id="fnref:21" href="#fn:21"><sup>21</sup></a><a class="footnote-ref" id="fnref:22" href="#fn:22"><sup>22</sup></a> This antioxidant ability results from both its antioxidant ability to reduce reactive oxygen species (derived from the part of the molecule containing plastoquinonol), which are often formed within mitochondria, as well as its ability to increase ion exchange across membranes (derived from the part of the molecule containing cations that can dissolve within membranes).<a class="footnote-ref" id="fnref:23" href="#fn:23"><sup>23</sup></a> Specifically, like plastoquinol, SkQ1 has been shown to scavenge superoxides both within cells (in vivo) and outside of cells (in vitro).<a class="footnote-ref" id="fnref:24" href="#fn:24"><sup>24</sup></a> SkQR1 and SkQ1 have also been proposed as a possible way to treat brain issues like <a href="/facts/Alzheimer%2527s_disease/w7Ad6tdg">Alzheimer's</a> due to their ability to potentially fix damages caused by <a href="/facts/Amyloid_beta/QkXy91f9">amyloid beta</a>.<a class="footnote-ref" id="fnref:25" href="#fn:25"><sup>25</sup></a> Additionally, SkQR1 has been shown as a way to reduce the issues caused by brain trauma through its antioxidant abilities, which help prevent cell death signals by reducing the amounts of reactive oxygen species coming from mitochondria.<a class="footnote-ref" id="fnref:26" href="#fn:26"><sup>26</sup></a> </p> <h2 id="external-links">External links</h2> <ul><li><a href="https://web.archive.org/web/20120305012738/http://www.cyberlipid.org/vitk/plas0002.htm">Plastoquinones</a> History, absorption spectra, and analogs.</li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Nowicka, Beatrycze; Kruk, Jerzy (2010-09-01). "Occurrence, biosynthesis and function of isoprenoid quinones". Biochimica et Biophysica Acta (BBA) - Bioenergetics. 1797 (9): 1587–1605. doi:10.1016/j.bbabio.2010.06.007. ISSN 0006-3002. PMID 20599680. <a href="https://doi.org/10.1016%2Fj.bbabio.2010.06.007" target="_blank">https://doi.org/10.1016%2Fj.bbabio.2010.06.007</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Nowicka, Beatrycze; Kruk, Jerzy (2010-09-01). "Occurrence, biosynthesis and function of isoprenoid quinones". Biochimica et Biophysica Acta (BBA) - Bioenergetics. 1797 (9): 1587–1605. doi:10.1016/j.bbabio.2010.06.007. ISSN 0006-3002. PMID 20599680. <a href="https://doi.org/10.1016%2Fj.bbabio.2010.06.007" target="_blank">https://doi.org/10.1016%2Fj.bbabio.2010.06.007</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Tikhonov, Alexander N. (2014-08-01). "The cytochrome b6f complex at the crossroad of photosynthetic electron transport pathways". Plant Physiology and Biochemistry. 81: 163–183. doi:10.1016/j.plaphy.2013.12.011. ISSN 1873-2690. PMID 24485217. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Mubarakshina, Maria M.; Ivanov, Boris N. (2010-10-01). "The production and scavenging of reactive oxygen species in the plastoquinone pool of chloroplast thylakoid membranes". Physiologia Plantarum. 140 (2): 103–110. Bibcode:2010PPlan.140..103M. doi:10.1111/j.1399-3054.2010.01391.x. ISSN 1399-3054. PMID 20553418. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Mubarakshina, Maria M.; Ivanov, Boris N. (2010-10-01). "The production and scavenging of reactive oxygen species in the plastoquinone pool of chloroplast thylakoid membranes". Physiologia Plantarum. 140 (2): 103–110. Bibcode:2010PPlan.140..103M. doi:10.1111/j.1399-3054.2010.01391.x. ISSN 1399-3054. PMID 20553418. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>http://dictionary.reference.com/browse/Plastoquinone Definition of plastoquinone <a href="http://dictionary.reference.com/browse/Plastoquinone" target="_blank">http://dictionary.reference.com/browse/Plastoquinone</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>Tikhonov, Alexander N. (2014-08-01). "The cytochrome b6f complex at the crossroad of photosynthetic electron transport pathways". Plant Physiology and Biochemistry. 81: 163–183. doi:10.1016/j.plaphy.2013.12.011. ISSN 1873-2690. PMID 24485217. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>Tikhonov, Alexander N. (2014-08-01). "The cytochrome b6f complex at the crossroad of photosynthetic electron transport pathways". Plant Physiology and Biochemistry. 81: 163–183. doi:10.1016/j.plaphy.2013.12.011. ISSN 1873-2690. PMID 24485217. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>Tikhonov, Alexander N. (2014-08-01). "The cytochrome b6f complex at the crossroad of photosynthetic electron transport pathways". Plant Physiology and Biochemistry. 81: 163–183. doi:10.1016/j.plaphy.2013.12.011. ISSN 1873-2690. PMID 24485217. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>Tikhonov, Alexander N. (2014-08-01). "The cytochrome b6f complex at the crossroad of photosynthetic electron transport pathways". Plant Physiology and Biochemistry. 81: 163–183. doi:10.1016/j.plaphy.2013.12.011. ISSN 1873-2690. PMID 24485217. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> <li id="fn:11"><p>Lambreva, Maya D.; Russo, Daniela; Polticelli, Fabio; Scognamiglio, Viviana; Antonacci, Amina; Zobnina, Veranika; Campi, Gaetano; Rea, Giuseppina (2014). "Structure/function/dynamics of photosystem II plastoquinone binding sites". Current Protein & Peptide Science. 15 (4): 285–295. doi:10.2174/1389203715666140327104802. ISSN 1875-5550. PMC 4030317. PMID 24678671. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4030317" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4030317</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li> <li id="fn:12"><p>Tikhonov, Alexander N. (2014-08-01). "The cytochrome b6f complex at the crossroad of photosynthetic electron transport pathways". Plant Physiology and Biochemistry. 81: 163–183. doi:10.1016/j.plaphy.2013.12.011. ISSN 1873-2690. PMID 24485217. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></p></li> <li id="fn:13"><p>Lambreva, Maya D.; Russo, Daniela; Polticelli, Fabio; Scognamiglio, Viviana; Antonacci, Amina; Zobnina, Veranika; Campi, Gaetano; Rea, Giuseppina (2014). "Structure/function/dynamics of photosystem II plastoquinone binding sites". Current Protein & Peptide Science. 15 (4): 285–295. doi:10.2174/1389203715666140327104802. ISSN 1875-5550. PMC 4030317. PMID 24678671. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4030317" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4030317</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></p></li> <li id="fn:14"><p>Tikhonov, Alexander N. (2014-08-01). "The cytochrome b6f complex at the crossroad of photosynthetic electron transport pathways". Plant Physiology and Biochemistry. 81: 163–183. doi:10.1016/j.plaphy.2013.12.011. ISSN 1873-2690. PMID 24485217. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></p></li> <li id="fn:15"><p>Lambreva, Maya D.; Russo, Daniela; Polticelli, Fabio; Scognamiglio, Viviana; Antonacci, Amina; Zobnina, Veranika; Campi, Gaetano; Rea, Giuseppina (2014). "Structure/function/dynamics of photosystem II plastoquinone binding sites". Current Protein & Peptide Science. 15 (4): 285–295. doi:10.2174/1389203715666140327104802. ISSN 1875-5550. PMC 4030317. PMID 24678671. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4030317" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4030317</a> <a href="#fnref:15" class="footnote-back-ref">↩</a></p></li> <li id="fn:16"><p>Nowicka, Beatrycze; Kruk, Jerzy (2010-09-01). "Occurrence, biosynthesis and function of isoprenoid quinones". Biochimica et Biophysica Acta (BBA) - Bioenergetics. 1797 (9): 1587–1605. doi:10.1016/j.bbabio.2010.06.007. ISSN 0006-3002. PMID 20599680. <a href="https://doi.org/10.1016%2Fj.bbabio.2010.06.007" target="_blank">https://doi.org/10.1016%2Fj.bbabio.2010.06.007</a> <a href="#fnref:16" class="footnote-back-ref">↩</a></p></li> <li id="fn:17"><p>Nowicka, Beatrycze; Kruk, Jerzy (2010-09-01). "Occurrence, biosynthesis and function of isoprenoid quinones". Biochimica et Biophysica Acta (BBA) - Bioenergetics. 1797 (9): 1587–1605. doi:10.1016/j.bbabio.2010.06.007. ISSN 0006-3002. PMID 20599680. <a href="https://doi.org/10.1016%2Fj.bbabio.2010.06.007" target="_blank">https://doi.org/10.1016%2Fj.bbabio.2010.06.007</a> <a href="#fnref:17" class="footnote-back-ref">↩</a></p></li> <li id="fn:18"><p>Nowicka, Beatrycze; Kruk, Jerzy (2010-09-01). "Occurrence, biosynthesis and function of isoprenoid quinones". Biochimica et Biophysica Acta (BBA) - Bioenergetics. 1797 (9): 1587–1605. doi:10.1016/j.bbabio.2010.06.007. ISSN 0006-3002. PMID 20599680. <a href="https://doi.org/10.1016%2Fj.bbabio.2010.06.007" target="_blank">https://doi.org/10.1016%2Fj.bbabio.2010.06.007</a> <a href="#fnref:18" class="footnote-back-ref">↩</a></p></li> <li id="fn:19"><p>F.F. Severina; I.I. Severina; Y.N. Antonenkoa; T.I. Rokitskayaa; D.A. Cherepanovb; E.N. Mokhovaa; M.Yu. Vyssokikha; A.V. Pustovidkoa; O.V. Markovaa; L.S. Yaguzhinskya; G.A. Korshunovaa; N.V. Sumbatyana; M.V. Skulacheva; V.P. Skulacheva (2009). "Penetrating cation/fatty acid anion pair as a mitochondria-targeted protonophore". Proc. Natl. Acad. Sci. U.S.A. 107 (2): 663–8. doi:10.1073/pnas.0910216107. PMC 2818959. PMID 20080732. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2818959" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2818959</a> <a href="#fnref:19" class="footnote-back-ref">↩</a></p></li> <li id="fn:20"><p>Skulachev, Vladimir P.; Anisimov, Vladimir N.; Antonenko, Yuri N.; Bakeeva, Lora E.; Chernyak, Boris V.; Erichev, Valery P.; Filenko, Oleg F.; Kalinina, Natalya I.; Kapelko, Valery I.; Kolosova, Natalya G.; Kopnin, Boris P.; Korshunova, Galina A.; Lichinitser, Mikhail R.; Obukhova, Lidia A.; Pasyukova, Elena G.; Pisarenko, Oleg I.; Roginsky, Vitaly A.; Ruuge, Enno K.; Senin, Ivan I.; Severina, Inna I.; Skulachev, Maxim V.; Spivak, Irina M.; Tashlitsky, Vadim N.; Tkachuk, Vsevolod A.; Vyssokikh, Mikhail Yu.; Yaguzhinsky, Lev S.; Zorov, Dmitry B. (2008). "An attempt to prevent senescence: A mitochondrial approach". Biochimica et Biophysica Acta (BBA) - Bioenergetics. 1787 (5): 437–461. doi:10.1016/j.bbabio.2008.12.008. PMID 19159610. <a href="https://doi.org/10.1016%2Fj.bbabio.2008.12.008" target="_blank">https://doi.org/10.1016%2Fj.bbabio.2008.12.008</a> <a href="#fnref:20" class="footnote-back-ref">↩</a></p></li> <li id="fn:21"><p>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 <a href="http://protein.bio.msu.ru/biokhimiya/contents/v73/pdf/bcm_1329.pdf" target="_blank">http://protein.bio.msu.ru/biokhimiya/contents/v73/pdf/bcm_1329.pdf</a> <a href="#fnref:21" class="footnote-back-ref">↩</a></p></li> <li id="fn:22"><p>Isaev, N. K.; Stelmashook, E. V.; Stelmashook, N. N.; Sharonova, I. N.; Skrebitsky, V. G. (2013-03-01). "Brain aging and mitochondria-targeted plastoquinone antioxidants of SkQ-type". Biochemistry. Biokhimiia. 78 (3): 295–300. doi:10.1134/S0006297913030127. ISSN 1608-3040. PMID 23586724. S2CID 10787334. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:22" class="footnote-back-ref">↩</a></p></li> <li id="fn:23"><p>Isaev, N. K.; Stelmashook, E. V.; Stelmashook, N. N.; Sharonova, I. N.; Skrebitsky, V. G. (2013-03-01). "Brain aging and mitochondria-targeted plastoquinone antioxidants of SkQ-type". Biochemistry. Biokhimiia. 78 (3): 295–300. doi:10.1134/S0006297913030127. ISSN 1608-3040. PMID 23586724. S2CID 10787334. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:23" class="footnote-back-ref">↩</a></p></li> <li id="fn:24"><p>Chistyakov, V. A.; Prazdnova, E. V.; Gutnikova, L. V.; Sazykina, M. A.; Sazykin, I. S. (July 2012). "Superoxide scavenging activity of plastoquinone derivative 10-(6'-plastoquinonyl)decyltriphenylphosphonium (SkQ1)". Biochemistry. Biokhimiia. 77 (7): 776–778. doi:10.1134/S0006297912070103. ISSN 1608-3040. PMID 22817541. S2CID 17313702. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:24" class="footnote-back-ref">↩</a></p></li> <li id="fn:25"><p>Isaev, N. K.; Stelmashook, E. V.; Stelmashook, N. N.; Sharonova, I. N.; Skrebitsky, V. G. (2013-03-01). "Brain aging and mitochondria-targeted plastoquinone antioxidants of SkQ-type". Biochemistry. Biokhimiia. 78 (3): 295–300. doi:10.1134/S0006297913030127. ISSN 1608-3040. PMID 23586724. S2CID 10787334. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:25" class="footnote-back-ref">↩</a></p></li> <li id="fn:26"><p>Isaev, N. K.; Novikova, S. V.; Stelmashook, E. V.; Barskov, I. V.; Silachev, D. N.; Khaspekov, L. G.; Skulachev, V. P.; Zorov, D. B. (September 2012). "Mitochondria-targeted plastoquinone antioxidant SkQR1 decreases trauma-induced neurological deficit in rat". Biochemistry. Biokhimiia. 77 (9): 996–999. doi:10.1134/S0006297912090052. ISSN 1608-3040. PMID 23157258. S2CID 11913685. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:26" class="footnote-back-ref">↩</a></p></li> </ol>