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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.
The electrons are transferred to plastoquinone and two protons, generating plastoquinol, which released into the membrane as a mobile electron carrier. This is the second core process in photosynthesis. The initial stages occur within picoseconds, with an efficiency of 100%. The seemingly impossible efficiency is due to the precise positioning ...
By providing an electron sink when the plastoquinone pool is over-reduced, the oxidase is thought to protect photosystem II from oxidative damage. Knockouts for Rubisco and photosystem II complexes, which would experience more photodamage than normal, exhibit an upregulation of plastid terminal oxidase. [6]
Photosystem II (or water-plastoquinone oxidoreductase) is the first protein complex in the energy-dependent reactions of oxygenic photosynthesis. It is located in the thylakoid membrane of plants , algae , and cyanobacteria .
More specifically, inhibition of HPPD prevents the formation of a breakdown product, homogentisic acid, which in turn is a key precursor for the biosynthesis of both tocopherols and plastoquinone. Plastoquinone is, in turn, a critical co-factor in the formation of carotenoids, which protect chlorophyll in plants from being destroyed by sunlight ...
Plastoquinone is a redox relay involved in photosynthesis. Pyrroloquinoline quinone is another biological redox cofactor. Ubiquinones, as their name implies, are ubiquitous in living creatures, being components of respiratory apparatus. Blattellaquinone, a sex pheromone in cockroaches. Quinones are conjectured to occur in all respiring ...
The cytochrome b6f complex is part of the thylakoid electron transport chain and couples electron transfer to the pumping of protons into the thylakoid lumen. Energetically, it is situated between the two photosystems and transfers electrons from photosystem II-plastoquinone to plastocyanin-photosystem I.
The electron transfers from pheophytin to plastoquinone (PQ), which takes 2e-(in two steps) from pheophytin, and two H + Ions from the stroma to form PQH 2. This plastoquinol is later oxidized back to PQ, releasing the 2e - to the cytochrome b 6 f complex and the two H + ions into the thylakoid lumen .