Back نظام ضوئي ثاني (II) Arabic Fotosystém II Czech Photosystem II German Fotosüsteem II Estonian Photosystème II French Fotosistema II Galician Fotosistem II ID Fotosistema II Italian 光化学系II Japanese 광계 II Korean
Photosystem II (or water-plastoquinone oxidoreductase) 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.
By replenishing lost electrons with electrons from the splitting of water, photosystem II provides the electrons for all of photosynthesis to occur. The hydrogen ions (protons) generated by the oxidation of water help to create a proton gradient that is used by ATP synthase to generate ATP. The energized electrons transferred to plastoquinone are ultimately used to reduce NADP+
to NADPH or are used in non-cyclic electron flow.[1] DCMU is a chemical often used in laboratory settings to inhibit photosynthesis. When present, DCMU inhibits electron flow from photosystem II to plastoquinone.
- ^ Loll B, Kern J, Saenger W, Zouni A, Biesiadka J (December 2005). "Towards complete cofactor arrangement in the 3.0 A resolution structure of photosystem II". Nature. 438 (7070): 1040–4. Bibcode:2005Natur.438.1040L. doi:10.1038/nature04224. PMID 16355230. S2CID 4394735.