Abstract:It has been demonstrated from our study that the preparations of free cells, thylakoid menbranes and PSII particles of the blue-green algae Spirulina maxima cultured under normal temperature all kept a great deal of O2-evolving activities. Meanwhile, the O2-evolving activities were increased along with the pruification of these preparation. The presence of Ca2+ in the isola-tion medium was essential to photosynthetic O2-evolution. SDS-PAGE profile indicated that the PSII particles contained 12 polypeptides, hence the composition of PSII polypeptides was more complicated than that of higher plant. The result of experiments of salt-treatment and polypeptides recomstitution suggested that the 55, 50, 26kD polypeptides were closely related to the extrinsic 02-evolving protein of PSII, especially the 55, 26kD polypeptides were essential to photosythetic 02-evolution.