Novel Photosystems in Acaryochloris Marina

  • Mr Shunsuke Ohashi, Institute of Materials Science, University of Tsukuba, Japan
  • Associate Prof Hideaki Miyashita, Dept. Technol. Ecol., Hall Global Environ. Res., Kyoto Univ., and Graduate School Human Environ. Stud., Kyoto Univ., Japan
  • Prof Tadashi Watanabe, Institute of Industrial Science, University of Tokyo, Japan
  • Dr Koji Iwamoto, Institute of Biological Sciences, University of Tsukuba, Japan
  • Prof Yoshihiro Shiraiwa, Institute of Biological Sciences, University of Tsukuba, Japan
  • Masami Kobayashi, Institute of Materials Science, University of Tsukuba, Japan

    • In 1996, a Chl d-dominated cyanobacteria Acaryochloris marina was discovered from colonial ascidians, and much research on the pigment composition of this unique organism has been performed. In A. marina cells, Chl a, Phe a and Chl d' are present as minor components as well as dominant Chl d. P740 was initially proposed to be a Chl d homodimer, later a Chl d' homodimer, and finally a Chl d/d' heterodimer, just like a Chl a/a' heterodimer for P700. The primary electron acceptor, A0, in PS I of A. marina is Chl a, supporting our hypothesis that Chl a derivative is a general feature of A0 in the PS I-type reaction centers (RCs). The secondary electron acceptors of PS I in A. marina have been identified as phylloquinone (PhQ). In the case of PS II of A. marina, whether Chl d acts as the special pair in PS II is a matter of controversy; it has been suggested that the special pair is a Chl d dimer, a Chl a dimer, or a Chl a/d heterodimer, while the identity of the primary electron acceptor of PS II in A. marina has been well defined as not Phe d but Phe a, like other cyanobacteria. Our heterodimer model of Chl a/d was recently supported in part by the difference spectra of the PS II RC of A. marina in the blue light region.