Definition of photosystem

A membrane-bound protein complex in plants and photosynthetic bacteria, responsible for light harvesting and primary electron transfer. Comprises light-harvesting pigments such as chlorophyll; a primary electron-transfer center, and secondary electron carriers. In green plant photosynthesis, Photosystem I transfers electrons from plastocyanin to a [2Fe-2S] ferredoxin, and contains iron-sulfur proteins. Photosystem II transfers electrons from the oxygen-evolving complex to plastoquinone, and contains an iron center.


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