Photosystem I reaction centers from Chlamydomonas and higher plant chloroplasts.

A photosystem I reaction center has been isolated from Chlamydomonas chloroplasts and compared with the photosystem I reaction center from higher plants. While the higher plant reaction center is active in cytochrome 552 photooxidation, the Chlamydomonas preparation was not active unless salts were included in the assay medium or the pH was lowered to 5. Subunit III-depleted photosystem I reaction center from higher plants is also inactive in cytochrome 552 photooxidation in the absence of salts. As with the Chlamydomonas reaction center, salts induced its activity. Subunit I of the photosystem I reaction center has tentatively been identified as the binding site of cytochrome 552.