A role for PsbZ in the core complex of photosystem II.

Photosynthesis in oxygen-evolving organisms is driven by electron transport through the photochemical reaction centers photosystem I (PSI) and photosystem II (PSII), two large protein complexes located in the chloroplast thylakoid membrane. PSI and PSII each contain an array of light-harvesting antenna pigments that absorb light energy and transfer it to a reaction center core complex, where electron transport drives the conversion of energy into the stable chemical products NADPH and ATP. PSII absorbs predominantly red light and produces a strong oxidant that extracts electrons from water and releases oxygen (the water-splitting reaction of photosynthesis) and a reductant that transfers electrons on to PSI. PSI absorbs predominantly far-red light plus electrons from PSII to produce a strong reductant capable of reducing NADP to NADPH. Light-driven ATP synthesis (photophosphorylation) is tightly coupled to electron transport through PSII and PSI and occurs within an ATP synthase complex embedded in the thylakoid membrane. Two other major complexes involved in photosynthetic energy conversion are cytochrome b 6 f , which controls the shuttle of electrons from PSII to PSI via the mobile electron carriers plastoquinone and plastocyanin, and LHCII, a light-harvesting protein complex that functions as an auxiliary antenna for PSII and also appears to influence energy distribution between PSI and PSII. Most of the proteins of these complexes, which together make up the photosynthetic apparatus, are encoded by the chloroplast genome. On the basis of the high degree of conservation of structure and composition of photosystems in all organisms examined to date, it is thought that all photosystems A Role for PsbZ in the Core Complex of Photosystem II