Abstract
We have reported that the types of the extrinsic proteins and their binding properties are different among higher plant, green algal, Euglena, red algal and cyanobacterial PSIIs. To compare the distribution and binding properties of the extrinsic proteins among plant species, PSII retaining all of the extrinsic proteins need to be prepared from the other species. In this study, PSII was attempted to prepare from a diatom, Chaetoceros gracilis. Thylakoid membranes prepared by freeze-thaw of the diatom cells were solubilized with SM and applied on a sucrose-density gradient centrifugation. The resulted PSII showed oxygen-evolving activity of about 500 μmol O2/mg chl/h and bound six extrinsic proteins of PsbO, PsbV, PsbQ' and three unknown proteins. Partial amino acid sequences of their unknown extrinsic proteins were determined. We will discuss evolution of oxygen-evolving PSII from a view of distribution of the extrinsic proteins.
