Photosystem II

Photosystem II (shown left - Note: Very large molecule! Please wait for it to load.) is remarkably similar in structure to the bacterial reaction centre and it is theorized that they share a common ancestor. Photosystem II is present in green plants, and is the photosystem that generates the electron that will eventually reduce NADP⁺. At least 22 polypeptides are associated with PSII, and it is surrounded by multiple antennae, including major distal LHCs - Outer light harvesting chlorophyll binding proteins (LHCBs), minor distal LHCs, and inner antenna complex, consisting of the 47 and 43kDa chl a/b binding proteins (CP47 and CP43). It is located on the thylakoid membranes inside chloroplasts, where the core proteins exist as dimers.

in thylakoid membrane - notice that the base is rich in green areas which represent aliphatic amino acids. These are hydrophobic, so favour alignment within the membrane, where water is excluded.

The core of photosystem II consists of D1 and D2 (It is the D1 subunit which suffers damage from active oxygen species in plants experiencing chronic photoinhibition). These two subunits are similar to the L and M subunits present in the bacterial reaction centre. Photosystem II differs from the bacterial reaction centre in that it has many additional subunits which bind additional chlorophylls to increase efficiency.

within PSII (colour-coding in keeping with focus on the bacterial reaction centre on previous page)

in on a reaction centre - notice the similarity to the bacterial photosynthetic reaction centre

chlorophyll molecules bound to antenna complexes