Evidence for a trimeric organization of the photosystem I complex from the thermophilic cyanobacteriumSynechococcussp.

A photosystem I (PS I) reaction center complex was isolated and purified from the cyanobacterium Synechococcus sp. The complex has a molecular mass of about 600 kDa and contains 120 Chl a molecules per photoactive Chl a I (P‐700). Electron micrographs show that the PS I complex has the shape of a disk with a diameter of about 19 nm and a thickness of 6 nm. Computer analysis reveals that the complex is composed of three similar units.