PARENT SESSION
Posters P2A Type I reaction centres. Abstracts (181-218)

The unique properties of Photosystem I of a cyanobacterium Gloeobacter violaceus PCC7421. Hidetoshi Inoue¹, Tohru Tsuchiya^{*,1, 2}, Soichirou Stoh³, Hideaki Miyashita^{1, 2}, Ayumi Tanaka³, Mamoru Mimuro^{1, 2}, ¹ Graduate School of Human and Environmental Studies, Japan² Department of Technology and Ecology, Japan³ The Institute of Low Temperature Science, Japan

ABSTRACT- Gloeobacter violaceus PCC 7421 is a unicellular cyanobacterium isolated from calcareous rock in mountainous regions of Switzerland. The most remarkable morphological characteristic is the lack of intracellular photosynthetic thylakoids, and the photosynthetic electron transfer system is localized in cytoplasmic membrane. Thus, the orthologs of lumenal subunits in other cyanobacteria, i.e., water oxidation components, are localized in periplasmic space. Phylogenetic analysis of the 16S rRNA sequences reveals that Gloeobacter was branched off at the earliest stage in the cyanobacterial tree. This may indicate that this species still retains primitive characteristics of cyanobacteria. We analyzed fluorescence properties of intact cells, and found that the long-wavelength chlorophyll fluorescence of PS I was absent [1]. We further isolated PS I trimer and characterized its biochemical and spectroscopic properties. The subunit composition of PS I trimer of Gloeobacter was very different from that of Synechocystis sp. PCC 6803; a few subunits were not detected in consistent with the genome information [2]. The PsaB of Gloeobacter had a long C-terminal extension, consisting of 155 amino acids. The P700 content was almost the same as in Synechocystis sp. PCC 6803. The long-wavelength chlorophyll fluorescence at 77 K was absent in the PS I trimer as in the case of intact cells, and this was confirmed by absence of the red chlorophyll resolved by the low temperature absorption spectrum. The unique features of PS I in Gloeobacter will be discussed based on the results of recent genomic sequencing [2]. [1] Mimuro, M. et al., Plant Cell Physiol. (2002) 43, 587. [2] Nakamura, Y. et al., DNA Res. (2003) 10, 137.

KEY WORDS: Photosystem I, Gloeobacter violaceus