Photosystem II
（重定向自PSII）
![Light-dependent reactions of photosynthesis at the thylakoid membrane](/Images/godic/202502/05/Thylakoid_membrane_3.svg1922.png")
![Cyanobacteria photosystem II, Dimer, PDB 2AXT](/Images/godic/202502/05/PhotosystemII1922.PNG")
![Cyanobacterial photosystem II, Monomer, PDB 2AXT.](/Images/godic/202502/05/Photosystem-II_2AXT1923.PNG")
![Proposed structure of Manganese Center](/Images/godic/202502/05/Manganese_cluster_in_the_oxygen-evolving_complex.svg1923.png")
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.