Director-General: Hideo Mohri
Associate Professor: Shigeru Itoh
Research Associates: Mamoru MimuroAKatsunori Aizawa
The former members of the Division of Bioenergetics have been included in the Office of Director.
Mamoru Mimuro
Primary processes in photosynthesis were studied in terms of structure-function relationship.
A primary electron donor in the photosystem (PS) II reaction center
(RC), P680, was shown to be a dimer based on the magnetic circular
dichroism (MCD) (Nozawa et al., 1995). An MCD signal is inversely
proportional to the association state of pigments, even though
its theoretical basis is not yet known. This relationship was
confirmed on RC and light harvesting II complexes isolated from
purple bacteria and artificial aggregates of bacteriochlorophyll
(BChl) c (Kobayashi et al., in press).
Two types of pheophytin (Pheo) molecules in the PS II RC was spectrally
discriminated. The photochemically active Pheo molecule has a
lower energy level than that of the photochemically inactive Pheo
molecule, which is analogous to the bacterial RC (Mimuro et al.,
1995). This confirms an evolutional linkage between bacterial
RC and PS II RC in oxygenic photosynthesis.
An antenna system of green photosynthetic bacteria, chlorosomes
was studied in term of relationship among morphology, molecular
structure and spectral properties (Wang et al., 1995). The hexanol-induced
changes on chlorosomes were explained by a direct interaction
between BChl c and hexanol, which consequently induced
a uni-directional elongation of rod elements and of chlorosomes.
In addition, we found a new component in chlorosomes which facilitates
a rapid energy migration from chlorosomes to the antenna in membranes
(Mimuro et al., in press).
A new approach for understanding of photosynthesis was started
by a collaboration entitled "Experimental
analyses of the origin of chloroplasts and phylogeny in algae".
Shigeru Itoh
Photosynthesis in plants and bacteria convert solar energy to electrochemical one in the reaction center (RC) complexes that are the molecular machines made of proteins and prosthetic groups. RC's seem to be established more than 3 billion years ago in the early Earth. We study the function of RC's, electron transfer systems, and their evolution by three approaches: 1) Exchange of the prosthetic groups by artificial compounds, 2) Genetic modification of the proteins, and 3) Exploration of new electron transfer systems. We replaced the phylloquinone (vitamin K1) in the RC complex of plant photosystem I by artificial quinones. The method enabled us to change the driving force of the reaction and clarified the optimization mechanism of the ultra-rapid electron transfer with a reaction time of 10-11 second by laser photolysis. Similar studies were also done in the newly purified RC of green bacteria that is a prototype of the plant RC. Mechanism of quinone reaction was also clarified in the genetically-modified oxidase of bacterial respiratory chain by cryogenic EPR. Surprisingly, we discovered a new organism that does not use Mg-chlorophyll but uses Zn-porphyrin in their photosynthesis. This opened a new stage in the study of photosynthesis that has been believed to be obligatory performed by Mg-chlorophyll's.
Demidov, A. A. and Mimuro, M. (1995) Deconvolution of C-Phycocyanin Beta-84 and Beta-155 chromophore absorption and fluorescence spectra of cyanobacterium Mastigocladus laminosus. Biophys. J. 68, 1500-1506.
Ikegami, I., Itoh, S.and Iwaki, M. (1995) Photoactive photosystem I particles with a molar ratio of Chlorophyll a to P700 of 9. Plant Cell Physiol. 36, 857-864.
Mimuro, M., Tomo, T., Nishimura, Y., Yamazaki, I. and Satoh, K. (1995) Identification of a photochemically inactive pheophytin molecule in the spinach D1-D2-cyt b559 complex. Biochim. Biophys. Acta 1232, 81-88.
Mohri, H., Kubo-Irie, M. and Irie, M. (1995) Outer arm dynein of sperm flagella and cilia in the animal kingdom. Méme. Mus. natn. Hist. nat. 166, 15-22.
Nozawa, T., Kobayashi, M., Itoh, S., Iwaki, M., Mimuro, M. and Satoh, K. (1995) Magnetic circular dichroism investigation of chlorophylls in reaction centers of photosystems I and II of green plant photosynthesis. Spectrochimica Acta 51A, 125-134.
Oh-oka, H., Kakutani, S., Kamei, S., Matsubara, H., Iwaki, M. and Itoh, S. (1995) Highly purified photosynthetic reaction center (PscA/Cytochrome c551)2 complex of the green sulfur bacterium Chlorobium limicola. Biochemistry 34, 13091-13097
Oh-oka, H., Kamei, S., Matsubara, H. and Iwaki, M. Itoh, S. (1995) Two cytochrome c heme function as the electron donor to P840 in the reaction center complex of a green sulfur bacterium, Chlorobium tepidum. FEBS Lett. 365, 30-34.
Sato-Watanabe, M., Itoh, S., Mogi, T., Matsuura, K., Miyoshi, H. and Anraku, Y. (1995) Stabilization of a semiquinone radical at the high affinity quinone binding site of the Escherichia coli bo-type ubiquinone oxidase. FEBS Lett. 374, 265-269.
Sonoike, K., Terashima, I., Iwaki, M. and Itoh, S. (1995) Site of destruction of photosystem I iron-sulfur centers in leaves of Cucumis sativus L. by weak illumination at chilling temperatures is A1, the phylloquinone acceptor. FEBS Lett. 362, 235-238.
Wang, Z.-Y., Marx, G., Umetsu, M., Kobayashi, M., Mimuro, M. and Nozawa, T. (1995) Morphology and spectroscopy of chlorosomes from Chlorobium tepidum by alcohol treatments. Biochim. Biophys. Acta 1232, 187-196.