Abstract
Recently, we succeeded in preparation of oxygen-evolving Photosystem II (PSII) particles from a mesophilic centric diatom, Chaetoceros gracilis. The PSII particles, however, contained a large amount of FCP and their activity was unstable. In this study, PSII complexes were purified from a moderate thermophilic centric diatom, Chaetoceros neogracile which grows optimally at 35 degrees celcius, to prepare a stable PSII complex. After the cells were disrupted by freeze-thawing, thylakoid membranes were isolated and then solubilized with Triton X-100. Crude PSII was prepared from the solubilized thylakoid membranes by centrifuged fractionation. After the crude PSII was solubilized again with Triton X-100, PSII was purified by ion-exchange column chromatography. The purified PSII in which FCP was completely removed showed high oxygen-evolving activity (about 2,000 μmol O2/mg Chl/h) and contained five extrinsic proteins of PsbO, PsbQ', PsbV, Psb31, PsbU. Heat-stability and pigment compositions of the pure PSII will be reported.
