Virtuelle (Nano) Welten: PDB Molecule of the Month 22: Photosystem I

Photosynthetic Cousins

Different photosystems are used by different photosynthetic organisms. Higher plants, algae, and some bacteria have the photosystem I shown here and a second one termed photosystem II. A low resolution structure of photosystem II is available in PDB entry 1fe1 (not shown here). Photosystem II uses water instead of plastocyanin as the donor of electrons to fill the hole left when the energized electron is passed up the chain. When it grabs electrons from a water molecule, photosystem II splits the water and releases oxygen gas. This reaction is the source of all of the oxygen that we breathe. Some photosynthetic bacteria contain a smaller photosynthetic reaction center, such as the one shown on the right (PDB entry 1prc). As in photosystem I, a stack of chlorophyll and other cofactors transfer a light-energized electron up to an energetic electron carrier.