| Budget Amount *help |
¥3,910,000 (Direct Cost: ¥3,400,000、Indirect Cost: ¥510,000)
Fiscal Year 2007: ¥2,210,000 (Direct Cost: ¥1,700,000、Indirect Cost: ¥510,000)
Fiscal Year 2006: ¥1,700,000 (Direct Cost: ¥1,700,000)
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| Research Abstract |
Diatoms are unicellular photosynthetic algae found throughout the world's oceans and freshwater, and constitute one of the most important producers of the phytoplankton communities in aquatic ecosystems and the global carbon cycle. In spite of their significance, little is known about Photosystem II (PSII) in diatoms. In this study, we succeeded for the first time in the preparation of thylakoid membranes and PSII particles retaining a high oxygen-evolving activity and all of the extrinsic proteins from a diatom, Chaetoceros gracilis. The diatom thylakoid membranes and PSII particles showed an oxygen - evolving activity of about 250 and 850 μmol 02/mg Chl/h in the absence of CaC12, respectively. The PSII particles contained fucoxanthin chlotophyll a/c-binding proteins in addition to main intrinsic proteins of CP47, CP43, 02, D1, cytochrome b559, and the anntena size was estimated to be 229 Chl a per 2 molecules of pheophytin. Five extrinsic proteins were 〓oichimoterically released from the diatom PSII particles by alkaline Tris-treatment.
Among these five extrinsic proteins, four proteins were red algal-type extrinsic proteins, namely, PsbO, PsbQ', PsbV and PsbU, whereas the other one was a novel, hypothetical protein. The gene encoding the novel extrinsic protein was cloned and sequenced. The deduced proteins contained three characteristic leader sequences targeted for chloroplast endoplasmic reticulum, chloroplast envelope and thylakoid membrane, respectively, indicating that the novel protein is encoded in the nuclear genome and constitutes one of the extrinsic proteins located in the lumenal side. The binding properrties and functions of the five extrinsic proteins will be examined by release-reconstitution experiments of their extrinsic proteins with PSII.
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