plastoquinone

From the plastoquinone pool, electrons pass through the cytochrome b6f complex.

In developing plastids, its activity prevents the over-reduction of the plastoquinone pool.

Ubiquinone, plastoquinone or menaquinone can act as acceptor in different species.

The protons are transported by the plastoquinone.

These are linked by plastoquinone, which does require energy to reduce cytochrome f for it is a sufficient reductant.

These carriers are plastoquinone and plastocyanin.

The negatively charged pheophytin radical quickly passes its extra electron to two consecutive plastoquinone molecules.

Genes in chloroplasts are selected for transcription according to the redox state of the electron carrier plastoquinone.

Upon one more plastoquinone oxidation, a second water molecule is formed and the irons return to a +3 oxidation state.

It uses the energy of sunlight to transfer electrons from water to a mobile electron carrier in the membrane called plastoquinone:

The oxidase catalyzes the transfer of four electrons from reduced plastoquinone to molecular oxygen to form water .

Photo-reduction of pheophytin occurs at temperatures as low as 100K, and is observed after the reduction of plastoquinone.

The electron travels from the phaeophytin molecule through two plastoquinone molecules, the first tightly bound, the second loosely bound.

This is followed by the step P680 pheophytin, and then on to plastoquinone, which occurs within the reaction center of PS II.

The electrons transfer from pheophytin to plastoquinone, then to plastocyanin, providing the energy for hydrogen ions (H) to be pumped into the thylakoid space.

The reduction of plastoquinone by ferredoxin during cyclic electron transport also transfers two protons from the stroma to the lumen.

By providing an electron sink when the plastoquinone pool is over-reduced, the oxidase is thought to protect photosystem II from oxidative damage.

Analysis of substrate specificity revealed that the enzyme almost exclusively catalyzes the reduction of plastoquinone over other quinones such as ubiquinone and duroquinone.

The enzyme captures photons of light to energize electrons that are then transferred through a variety of coenzymes and cofactors to reduce plastoquinone to plastoquinol.

Two electrons are required to fully reduce the loosely bound plastoquinone molecule to QH as well as the uptake of two protons.

Plastid terminal oxidase catalyzes the oxidation of the plastoquinone pool, which exerts a variety of effects on the development and functioning of plant chloroplasts.

Without the enzyme, the carotenoid synthesis pathway slows down due to the lack of oxidized plastoquinone with which to oxidize phytoene, a carotenoid intermediate.

In the first step common to all proposed mechanisms, one plastoquinone is oxidized and both irons are reduced from iron(III) to iron(II).

Therefore, more experiments ensued to prove that pheophytin is indeed the primary electron acceptor of PSII, occurring between P680 and plastoquinone.

Robert Hill thought that a complex of reactions consisting of an intermediate to cytochrome b (now a plastoquinone), another is from cytochrome f to a step in the carbohydrate-generating mechanisms.