Mechanisms of Electron Flow in Photosystem II and Toward Photosystem I

In the thylakoid membrane of chloroplasts, the conversion of light into chemical energy is accomplished via a series of reactions that include two photoreactions, the primary reactions of two photosystems. Photosystem II (PS II) oxidizes water and reduces plastoquinone. Photosystem I (PS I) oxidizes plastocyanin and reduces ferredoxin and, via the ferredoxin, reduces NADP/sup +/. This series of reactions also leads to the phosphorylation of ADP to ATP via protons translocated across the membrane. Central subjects of this review are (a) the oxidation of water and (b) the redox reactions of plastoquinone.