THE EXTRINSIC PROTEINS OF PHOTOSYSTEM-II IN PHOTOSYNTHETIC ORGANISMS - DISTRIBUTION, PROPERTIES AND EVOLUTIONARY IMPLICATIONS

Photosystem II from higher plant chloroplasts contains extrinsic prote ins of molecular weights 33, 23 and 16 kDa. Cyanobacteria, which are t hought to be closely related to the evolutionary progenitor of chlorop lasts, have a protein homologous to the largest of these, but lack hom ologues of the smaller ones. Here we report immunological evidence for the occurrence of the 33 kDa extrinsic protein in red and chromophyte algae and its absence from anoxygenic photosynthetic bacteria. The 23 kDa protein was absent from all three groups. The red algal protein w as found to be hydrophilic and rather more loosely associated with the thylakoid membrane than its higher plant equivalent. These findings s upport an origin for all plastids among the oxygenic prokaroytes, in c ontrast to the phylogeny inferred from ribulose bisphosphate carboxyla se-oxygenase sequence data. (C) 1994 Academic Press, Inc.