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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.
NADH dehydrogenase → plastoquinol → b 6 f → cyt c 6 → cyt aa 3 → O 2. where the mobile electron carriers are plastoquinol and cytochrome c 6, while the proton pumps are NADH dehydrogenase, cyt b 6 f and cytochrome aa 3 (member of the COX3 family). Cyanobacteria are the only bacteria that produce oxygen during photosynthesis.
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 ...
The cytochrome b 6 f complex is a dimer, with each monomer composed of eight subunits. [3] These consist of four large subunits: a 32 kDa cytochrome f with a c-type cytochrome, a 25 kDa cytochrome b 6 with a low- and high-potential heme group, a 19 kDa Rieske iron-sulfur protein containing a [2Fe-2S] cluster, and a 17 kDa subunit IV; along with four small subunits (3-4 kDa): PetG, PetL, PetM ...
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.
Cytochrome f is the largest subunit of cytochrome b 6 f complex (plastoquinol—plastocyanin reductase; EC 1.10.99.1).In its structure and functions, the cytochrome b6f complex bears extensive analogy to the cytochrome bc1 complex of mitochondria and photosynthetic purple bacteria.
This page was last edited on 20 October 2005, at 19:14 (UTC).; Text is available under the
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. The electrons then pass through Cyt b 6 and Cyt f to plastocyanin , using energy from photosystem I to pump hydrogen ions (H + ) into the thylakoid space.