Plastoquinone

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Plastoquinone
Plastoquinone.png
Names
Preferred IUPAC name
2,3-Dimethyl-5-[(2E,6'E,10E,14E,18E,22E,26E,30E)-3,7,11,15,19,23,27,31,35-nonamethylhexatriaconta-2,6,10,14,18,22,26,30,34-nonaen-1-yl]cyclohexa-2,5-diene-1,4-dione
Identifiers
3D model (JSmol)
ChemSpider
PubChem CID
UNII
  • InChI=1S/C53H80O2/c1-40(2)21-13-22-41(3)23-14-24-42(4)25-15-26-43(5)27-16-28-44(6)29-17-30-45(7)31-18-32-46(8)33-19-34-47(9)35-20-36-48(10)37-38-51-39-52(54)49(11)50(12)53(51)55/h21,23,25,27,29,31,33,35,37,39H,13-20,22,24,26,28,30,32,34,36,38H2,1-12H3/b41-23+,42-25+,43-27+,44-29+,45-31+,46-33+,47-35+,48-37- X mark.svgN
    Key: FKUYMLZIRPABFK-RLAZMVNUSA-N X mark.svgN
  • CC=1C(=O)/C=C(/C\C=C(\C)CC\C=C(/C)CC\C=C(/C)CC\C=C(/C)CC\C=C(/C)CC\C=C(/C)CC\C=C(/C)CC\C=C(/C)CC\C=C(/C)C)C(=O)C=1C
Properties
C53H80O2
Molar mass 749.221 g·mol−1
Related compounds
Related compounds
 1,4-benzoquinone quinone coenzyme Q10
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
X mark.svgN  verify  (what is  Yes check.svgYX mark.svgN ?)

Plastoquinone (PQ) is a terpenoid-quinone (meroterpenoid) molecule involved in the electron transport chain in the light-dependent reactions of photosynthesis. The most common form of plastoquinone, known as PQ-A or PQ-9, is a 2,3-dimethyl-1,4-benzoquinone molecule with a side chain of nine isoprenyl units. There are other forms of plastoquinone, such as ones with shorter side chains like PQ-3 (which has 3 isoprenyl side units instead of 9) as well as analogs such as PQ-B, PQ-C, and PQ-D, which differ in their side chains. [1] The benzoquinone and isoprenyl units are both nonpolar, anchoring the molecule within the inner section of a lipid bilayer, where the hydrophobic tails are usually found. [1]

Contents

Plastoquinones are 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 oxidation states: plastoquinone, plastosemiquinone (unstable), and plastoquinol, which differs from plastoquinone by having two hydroxyl groups instead of two carbonyl groups. [2]

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. [3] One example of how it does this is by reacting with superoxides to form hydrogen peroxide and plastosemiquinone. [3]

The reduction (from left to right) of plastoquinone (PQ) to plastosemiquinone (PQH ) to plastoquinol (PQH2). Plastoquinone reduction.png
The reduction (from left to right) of plastoquinone (PQ) to plastosemiquinone (PQH ) to plastoquinol (PQH2).

The prefix plasto- means either plastid or chloroplast, alluding to its location within the cell. [4]

Role in photosynthesis

The structure of photosystem II is shown above, with the flow of electrons detailed by the red arrows. Plastoquinone binding sites QA and QB are included in this flow of electrons, with plastoquinol leaving QB to participate in the next step of the light-dependent reactions. Photosystem II - multilingual.svg
The structure of photosystem II is shown above, with the flow of electrons detailed by the red arrows. Plastoquinone binding sites QA and QB are included in this flow of electrons, with plastoquinol leaving QB to participate in the next step of the light-dependent reactions.

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 thylakoid. [2]

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 plastocyanin, a mobile, water-soluble electron carrier, through the cytochrome b6f protein complex. [2] The cytochrome b6f protein complex catalyzes the electron transfer between plastoquinone and plastocyanin, but also transports the two protons into the lumen of thylakoid discs. [2] This proton transfer forms an electrochemical gradient, which is used by ATP synthase at the end of the light dependent reactions in order to form ATP from ADP and Pi. [2]

Within photosystem II

Plastoquinone 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. [5] 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 in the membrane of the thylakoid. [2] [5] The free plastoquinone molecules eventually transfer electrons to the water-soluble plastocyanin so as to continue the light-dependent reactions. [2] There are additional plastoquinone binding sites within photosystem II (QC and possibly QD), but their function and/or existence have not been fully elucidated. [5]

Biosynthesis

The p-hydroxyphenylpyruvate is synthesized from tyrosine, while the solanesyl diphosphate is synthesized through the MEP/DOXP pathway. Homogentisate is formed from p-hydroxyphenylpyruvate and is then combined with solanesyl diphosphate through a condensation reaction. The resulting intermediate, 2-methyl-6-solanesyl-1,4-benzoquinol is then methylated to form the final product, plastoquinol-9. [1] This pathway is used in most photosynthetic organisms, like algae and plants. [1] However, cyanobacteria appear to not use homogentisate for synthesizing plastoquinol, possibly resulting in a pathway different from the one shown below. [1]

Biosynthesis pathway of PQ-9 with intermediates in blue, enzymes in black, and additional pathways in green. Plastoquinone Biosynthesis Pathway In Plants.png
Biosynthesis pathway of PQ-9 with intermediates in blue, enzymes in black, and additional pathways in green.

Derivatives

Some derivatives that were designed to penetrate mitochondrial cell membranes (SkQ1 (plastoquinonyl-decyl-triphenylphosphonium), SkQR1 (the rhodamine-containing analog of SkQ1), SkQ3) have anti-oxidant and protonophore activity. [6] SkQ1 has been proposed as an anti-aging treatment, with the possible reduction of age-related vision issues due to its antioxidant ability. [7] [8] [9] 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). [9] Specifically, like plastoquinol, SkQ1 has been shown to scavenge superoxides both within cells (in vivo) and outside of cells (in vitro). [10] SkQR1 and SkQ1 have also been proposed as a possible way to treat brain issues like Alzheimer's due to their ability to potentially fix damages caused by amyloid beta. [9] 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. [11]

Related Research Articles

<span class="mw-page-title-main">Oxidative phosphorylation</span> Metabolic pathway

Oxidative phosphorylation or electron transport-linked phosphorylation or terminal oxidation is the metabolic pathway in which cells use enzymes to oxidize nutrients, thereby releasing chemical energy in order to produce adenosine triphosphate (ATP). In eukaryotes, this takes place inside mitochondria. Almost all aerobic organisms carry out oxidative phosphorylation. This pathway is so pervasive because it releases more energy than alternative fermentation processes such as anaerobic glycolysis.

A proton pump is an integral membrane protein pump that builds up a proton gradient across a biological membrane. Proton pumps catalyze the following reaction:

<span class="mw-page-title-main">Thylakoid</span> Membrane enclosed compartments in chloroplasts and cyanobacteria

Thylakoids are membrane-bound compartments inside chloroplasts and cyanobacteria. They are the site of the light-dependent reactions of photosynthesis. Thylakoids consist of a thylakoid membrane surrounding a thylakoid lumen. Chloroplast thylakoids frequently form stacks of disks referred to as grana. Grana are connected by intergranal or stromal thylakoids, which join granum stacks together as a single functional compartment.

<span class="mw-page-title-main">Chloroplast membrane</span>

Chloroplasts contain several important membranes, vital for their function. Like mitochondria, chloroplasts have a double-membrane envelope, called the chloroplast envelope, but unlike mitochondria, chloroplasts also have internal membrane structures called thylakoids. Furthermore, one or two additional membranes may enclose chloroplasts in organisms that underwent secondary endosymbiosis, such as the euglenids and chlorarachniophytes.

<span class="mw-page-title-main">Chemiosmosis</span> Electrochemical principle that enables cellular respiration

Chemiosmosis is the movement of ions across a semipermeable membrane bound structure, down their electrochemical gradient. An important example is the formation of adenosine triphosphate (ATP) by the movement of hydrogen ions (H+) across a membrane during cellular respiration or photosynthesis.

<span class="mw-page-title-main">Photosystem</span> Structural units of protein involved in photosynthesis

Photosystems are functional and structural units of protein complexes involved in photosynthesis. Together they carry out the primary photochemistry of photosynthesis: the absorption of light and the transfer of energy and electrons. Photosystems are found in the thylakoid membranes of plants, algae, and cyanobacteria. These membranes are located inside the chloroplasts of plants and algae, and in the cytoplasmic membrane of photosynthetic bacteria. There are two kinds of photosystems: PSI and PSII.

<span class="mw-page-title-main">Photosystem II</span> First protein complex in light-dependent reactions of oxygenic photosynthesis

Photosystem II is the first protein complex in the light-dependent reactions of oxygenic photosynthesis. It is located in the thylakoid membrane of plants, algae, and cyanobacteria. Within the photosystem, enzymes capture photons of light to energize electrons that are then transferred through a variety of coenzymes and cofactors to reduce plastoquinone to plastoquinol. The energized electrons are replaced by oxidizing water to form hydrogen ions and molecular oxygen.

<span class="mw-page-title-main">Photosystem I</span> Second protein complex in photosynthetic light reactions

Photosystem I is one of two photosystems in the photosynthetic light reactions of algae, plants, and cyanobacteria. Photosystem I is an integral membrane protein complex that uses light energy to catalyze the transfer of electrons across the thylakoid membrane from plastocyanin to ferredoxin. Ultimately, the electrons that are transferred by Photosystem I are used to produce the moderate-energy hydrogen carrier NADPH. The photon energy absorbed by Photosystem I also produces a proton-motive force that is used to generate ATP. PSI is composed of more than 110 cofactors, significantly more than Photosystem II.

<span class="mw-page-title-main">Photophosphorylation</span> Biochemical process in photosynthesis

In the process of photosynthesis, the phosphorylation of ADP to form ATP using the energy of sunlight is called photophosphorylation. Cyclic photophosphorylation occurs in both aerobic and anaerobic conditions, driven by the main primary source of energy available to living organisms, which is sunlight. All organisms produce a phosphate compound, ATP, which is the universal energy currency of life. In photophosphorylation, light energy is used to pump protons across a biological membrane, mediated by flow of electrons through an electron transport chain. This stores energy in a proton gradient. As the protons flow back through an enzyme called ATP synthase, ATP is generated from ADP and inorganic phosphate. ATP is essential in the Calvin cycle to assist in the synthesis of carbohydrates from carbon dioxide and NADPH.

Cytochrome b<sub>6</sub>f complex Enzyme

The cytochrome b6f complex (plastoquinol/plastocyanin reductase or plastoquinol/plastocyanin oxidoreductase; EC 7.1.1.6) is an enzyme found in the thylakoid membrane in chloroplasts of plants, cyanobacteria, and green algae, that catalyzes the transfer of electrons from plastoquinol to plastocyanin:

<span class="mw-page-title-main">Cytochrome f</span>

Cytochrome f is the largest subunit of cytochrome b6f complex. In its structure and functions, the cytochrome b6f complex bears extensive analogy to the cytochrome bc1 complex of mitochondria and photosynthetic purple bacteria. Cytochrome f plays a role analogous to that of cytochrome c1, in spite of their different structures.

<span class="mw-page-title-main">Electrochemical gradient</span> Gradient of electrochemical potential, usually for an ion that can move across a membrane

An electrochemical gradient is a gradient of electrochemical potential, usually for an ion that can move across a membrane. The gradient consists of two parts:

<span class="mw-page-title-main">Light-harvesting complexes of green plants</span> Component of photosynthesis

The light-harvesting complex is an array of protein and chlorophyll molecules embedded in the thylakoid membrane of plants and cyanobacteria, which transfer light energy to one chlorophyll a molecule at the reaction center of a photosystem.

<span class="mw-page-title-main">Photosynthetic reaction centre</span> Molecular unit responsible for absorbing light in photosynthesis

A photosynthetic reaction center is a complex of several proteins, pigments and other co-factors that together execute the primary energy conversion reactions of photosynthesis. Molecular excitations, either originating directly from sunlight or transferred as excitation energy via light-harvesting antenna systems, give rise to electron transfer reactions along the path of a series of protein-bound co-factors. These co-factors are light-absorbing molecules (also named chromophores or pigments) such as chlorophyll and pheophytin, as well as quinones. The energy of the photon is used to excite an electron of a pigment. The free energy created is then used, via a chain of nearby electron acceptors, for a transfer of hydrogen atoms (as protons and electrons) from H2O or hydrogen sulfide towards carbon dioxide, eventually producing glucose. These electron transfer steps ultimately result in the conversion of the energy of photons to chemical energy.

<span class="mw-page-title-main">Pheophytin</span> Chlorophyll molecules lacking a central Mg2+ ion

Pheophytin or phaeophytin is a chemical compound that serves as the first electron carrier intermediate in the electron transfer pathway of Photosystem II in plants, and the type II photosynthetic reaction center found in purple bacteria. In both PS II and RC P870, light drives electrons from the reaction center through pheophytin, which then passes the electrons to a quinone (QA) in RC P870 and RC P680. The overall mechanisms, roles, and purposes of the pheophytin molecules in the two transport chains are analogous to each other.

Dioxygen plays an important role in the energy metabolism of living organisms. Free oxygen is produced in the biosphere through photolysis of water during photosynthesis in cyanobacteria, green algae, and plants. During oxidative phosphorylation in cellular respiration, oxygen is reduced to water, thus closing the biological water-oxygen redox cycle.

<span class="mw-page-title-main">Light-dependent reactions</span> Photosynthetic reactions

Light-dependent reactions refers to certain photochemical reactions that are involved in photosynthesis, the main process by which plants acquire energy. There are two light dependent reactions, the first occurs at photosystem II (PSII) and the second occurs at photosystem I (PSI).

SkQ is a class of mitochondria-targeted antioxidants, developed by Professor Vladimir Skulachev and his team. In a broad sense, SkQ is a lipophilic cation, linked via saturated hydrocarbon chain to an antioxidant. Due to its lipophilic properties, SkQ can effectively penetrate through various cell membranes. The positive charge provides directed transport of the whole molecule including antioxidant moiety into the negatively charged mitochondrial matrix. Substances of this type, various drugs that are based on them, as well as methods of their use are patented in Russia and other countries such as United States, China, Japan, and in Europe. Sometimes the term SkQ is used in a narrow sense for the denomination of a cationic derivative of the plant antioxidant plastoquinone.

<span class="mw-page-title-main">Chlororespiration</span>

Chlororespiration is a respiratory process that takes place within plants. Inside plant cells there is an organelle called the chloroplast which is surrounded by the thylakoid membrane. This membrane contains an enzyme called NAD(P)H dehydrogenase which transfers electrons in a linear chain to oxygen molecules. This electron transport chain (ETC) within the chloroplast also interacts with those in the mitochondria where respiration takes place. Photosynthesis is also a process that Chlororespiration interacts with. If photosynthesis is inhibited by environmental stressors like water deficit, increased heat, and/or increased/decreased light exposure, or even chilling stress then chlororespiration is one of the crucial ways that plants use to compensate for chemical energy synthesis.

Plastid terminal oxidase or plastoquinol terminal oxidase (PTOX) is an enzyme that resides on the thylakoid membranes of plant and algae chloroplasts and on the membranes of cyanobacteria. The enzyme was hypothesized to exist as a photosynthetic oxidase in 1982 and was verified by sequence similarity to the mitochondrial alternative oxidase (AOX). The two oxidases evolved from a common ancestral protein in prokaryotes, and they are so functionally and structurally similar that a thylakoid-localized AOX can restore the function of a PTOX knockout.

References

  1. 1 2 3 4 5 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.
  2. 1 2 3 4 5 6 7 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.
  3. 1 2 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. doi:10.1111/j.1399-3054.2010.01391.x. ISSN   1399-3054. PMID   20553418.
  4. ↑ http://dictionary.reference.com/browse/Plastoquinone Definition of plastoquinone
  5. 1 2 3 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.
  6. ↑ 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.
  7. ↑ 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.
  8. ↑ 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
  9. 1 2 3 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.
  10. ↑ 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.
  11. ↑ 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.
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