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J. Biol. Chem., Vol. 283, Issue 26, 18198-18209, June 27, 2008

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Characterization of Highly Purified Photosystem I Complexes from the Chlorophyll d-dominated Cyanobacterium Acaryochloris marina MBIC 11017^*

Tatsuya Tomo¹, Yuki Kato, Takehiro Suzuki^¶, Seiji Akimoto^||**, Tatsunori Okubo, Takumi Noguchi, Koji Hasegawa, Tohru Tsuchiya^¶¶, Kazunori Tanaka^||||, Michitaka Fukuya^||||, Naoshi Dohmae^¶, Tadashi Watanabe, and Mamoru Mimuro^¶¶

From the Department of Technology and Ecology, Hall of Global Environmental Research, Kyoto University, Kyoto 606-8501, Institute of Industrial Science, University of Tokyo, Tokyo 153-8505, ^¶Biomolecular Characterization Team, RIKEN, Wako, Saitama 351-0198, ^||Molecular Photoscience Research Center, Kobe University, Kobe 657-8501, ^**Graduate School of Science, Kobe University, Kobe 657-8501, Institute of Materials Science, University of Tsukuba, Tsukuba, Ibaraki 305-8573, Advancesoft Corporation, Tokyo 107-0052, ^¶¶Graduate School of Human and Environmental Studies, Kyoto University, Kyoto 606-8501, and ^||||Faculty of Science, Kobe University, Kobe 657-8501, Japan

Photochemically active photosystem (PS) I complexes were purified from the chlorophyll (Chl) d-dominated cyanobacterium Acaryochloris marina MBIC 11017, and several of their properties were characterized. PS I complexes consist of 11 subunits, including PsaK1 and PsaK2; a new small subunit was identified and named Psa27. The new subunit might replace the function of PsaI that is absent in A. marina. The amounts of pigments per one molecule of Chl d' were 97.0 ± 11.0 Chl d, 1.9 ± 0.5 Chl a, 25.2 ± 2.4 -carotene, and two phylloquinone molecules. The light-induced Fourier transform infrared difference spectroscopy and light-induced difference absorption spectra reconfirmed that the primary electron donor of PS I (P740) was the Chl d dimer. In addition to P740, the difference spectrum contained an additional band at 728 nm. The redox potentials of P740 were estimated to be 439 mV by spectroelectrochemistry; this value was comparable with the potential of P700 in other cyanobacteria and higher plants. This suggests that the overall energetics of the PS I reaction were adjusted to the electron acceptor side to utilize the lower light energy gained by P740. The distribution of charge in P740 was estimated by a density functional theory calculation, and a partial localization of charge was predicted to P1 Chl (special pair Chl on PsaA). Based on differences in the protein matrix and optical properties of P740, construction of the PS I core in A. marina was discussed.

Received for publication, March 6, 2008 , and in revised form, April 17, 2008.

^* This work was supported by Grant-in-aid for Creative Scientific Research 17GS0314 from the Japanese Society for the Promotion of Science (to M .M. and T. N.), by Scientific Research on Priority Areas Grants 17018022 and 18017016 from the Ministry of Education, Sports, Culture, Science, and Technology, Japan (to M. M.), by Grants-in-aid for Scientific Research 19614007 (to T. Tomo), 18350067 (to S. A.), and 18570145 (to T. N.), by Grant-in-aid for Scientific Research (C) 19614003 from the Japanese Society for the Promotion of Science, and a global Center of Excellence program for "Chemistry Innovation through Cooperation of Science and Engineering" from Ministry of Education, Sports, Culture, Science, and Technology, Japan (to Y. K. and T. W.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The on-line version of this article (available at http://www.jbc.org) contains supplemental Fig. 1 and additional references.

¹ To whom correspondence should be addressed. Tel.: 81-75-753-9375; Fax: 81-75-753-9375; E-mail: tomo{at}z05.mbox.media.kyoto-u.ac.jp.

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