NATIONAL INSTITUTE FOR BASIC BIOLOGY
DIVISION OF BIOENERGETICS
- Yoshihiko Fujita
- Associate Professor:
- Sigeru Itoh
- Research Associates:
- Mamoru Mimuro
- Visiting Scientist:
- Sung-Jun Kim *
- JSPS-Post-doctral Fellow:
- Tohru lkeya
- Vlsiting Fellow:
- Yuji Nakajima **
- Technical Staff:
- Akio Murakami
- ( * from Kyngpook National University)
( ** from Advanced Technology Research Center Mitsubishi Heavy
Oxygenic photosynthesis is an energy yielding metabolism that supports
autotrophic life of plants. Primary process of photosynthesis, Iight-energy
conversion, in thylakoids is the target for the study of this research
division. The research has been conducted for regulatory aspects of thylakoid
system in response to photosynthetic environments and also for molecular
mechanism of light-capturing and conversion in functional molecules.
I. Regulation of PSI/PSII stoichiometry
- Light-energy conversion in oxygenic photosynthesis is driven by the two
light reactions of the two photosystems, PSI and PSII. Imbalance
between the two light reactions causes lowering the efficiency of
energy conversion. Our previous study with cyanophytes has revealed
that plants have an ability for regulating the stoichiometry of the two
photosystems so as to compensate imbalance between the two light
reactions. Further, at least in the cyanophyte Synechocystis PCC 6714,
the stoichiometry is regulated by the control of PSI formation, which
occurs in response to the signal comming from the state of the electron
transport between the two photosystems.
Controlling mechanism for PSI formation has been conducted in two ways;
determining the target sites for regulation (1)in Chl a synthesis and
(2)in apoprotein synthesis. Analysis for dynamics of intermediates of
Chl a synthesis yielded following results (Fujita et al., in press):
(1) Pchlide reduction is regulated in parallel with regulation of PSI
formation. The activity is suppressed under conditions for suppression
of PSI formation, such as light regime preferentially exciting PSI (PSI
Iight). The suppression is released by the conditions for stimulation
of PSI formation, such as light regime exciting preferentially PSII
(PSII light). (2) Changes in the activity of Pchlide reduction are
neither due to acceleration-deceleration of PSI synthesis nor due to
differential occurrence of light-dependent Pchlide reduction. The
enzyme activity itself is regulated. Analysis for synthesis of PsaA/B
peptides, core peptides of PSI complex, with pulse-labeling method
revealed that (1) inhibitors for peptide elongation suppresses PsaA/B
synthesis differently in accelerated and decelerated PSI formations.
Inhibition at low inhibitor concentrations was stronger in the former
than that in the latter, suggesting that pausing of pepetide elongation
becomes longer under conditions for suppression of PSI formation. (2)
The inhibitor for initiation of translation showed similar effect. (3)
Effect of chrolamphenicol suggested that initiation of translation is
also regulated; it is suppressed by PSI Iight, and PSII light releases
from suppression. Together with previous results, evidences obtained
show that regulation of PSI formation in PSI/PSII adjustment occurs at
the translation level of PsaA/B synthesis. Since Chl a stabilizes
PsaA/B peptides, we assume that regulation of psaA/B expression at
translation level is achieved at least by Chl a supply.
- Changes in thylakoid composition in the green alga Chlamydomonas
reinhardtii in response to light quality were determined under
collaboration with Dr. A. Melis (Univ. Cal., Berkeley). Results indicated
that the pattern of change was similar to that in the cyanophyte
Synechocystis PCC 6714. Abundance of PSI was markedly changed while that
of PSII and Cyt b6-f remained fairly constant, resulting higher PSI/PSII
ratio under PSI Iight and lower ratio under PSI Iight. Changes in
PSI/PSII improved photosynthetic efficiency under respective light
regimes. Differently from cyanophyte system, a marked decrease in LHC, in
parallel with PSI decrease, occurred under PSI Iight. Results suggest
that Chl supply to assembling of Chl-protein complexes is a primary
determinant for adjustment of PSI/PSII stoichiometry in this organism
II. Mechanism of energy transfer in light-capturing pigment
- Examination was made for function of carotenoids in photosynthesis.
Relationship between molecular structure and optical properties in the
excited state was mainly analyzed. (1) The forbidden S1 state of
neurosporene and spheroidene, which is responsible for the energy
transfer to bacteriochlorophylls a, was directly measured by the
one-photon absorption spectroscopy; the energy level was higher than and
close to that of acceptors. (2) It was proved that the relaxation
processes from the excited state of carotenoids follow the energy gap law
of internal conversion. Presence of a keto carbonyl group induced a rapid
internal conversion to the S1 state, which was favorable for energy
transfer to chlorophylls a. This corresponds to the case for fucoxanthin
in brown algae and diatom. (3) The S2 Iifetime of B-carotene was directly
measured by the up-conversion method to be 195 +- 10 fs with an isotropy
ratio of 0.39 +- 0.02. (4) Theoretical analysis of the energy transfer
processes was carried out by calculation of the energy transfer matrix
elements between neurosporene and bacteriochlorophyll a. The electron
exchange mechnism is concluded to be less probable, even if the forbidden
singlet state is involved. (5) Based on these results, the energy
transfer through the dipole-multipole interaction from the Sl state to
(bacterio)chlorophyll a is proposed.
III. Mechnism of electron transfer in reaction center complex
- Mechanism of the primary photoenergy conversion in photosynthesis was
studied in plant and bacterial systems by the combination of modern
spectroscopy, and the biochemical and genetical manipulation of the
protein complexes. In the PSI reaction center complex, the time constant
for the primary charge separation between the electron donor chlorophyll
(P700) and the acceptor chlorophyll was measured to be 7 x 10^(-12) s.
The following reaction with phylloquinone was shown to take place with a
time constant of 38 x 10^(-12) s The rate varied when various artificial
quinones were introduced into the reaction center complex in place of
native phylloquinone. Functions of quinones in various reaction center
preparations were also studied. It is shown that the fine adjustment of
the energy levels of native electron transfer components enable the
highly efficient, ultra-fast electron transfer reactions. We isolated and
characterized the reaction center complex of green bacteria, which seems
to be ancestry to PSI reaction center. The complex was shown to have a
polypeptide composition simpler than that of plant PSI but to undergo
almost similar activities. Unique nature of the iron-sulfur centers in
this complex was shown by cryogenic EPR studies. The structurefunction
relationship of the iron-sulfur centers of the photosynthetic bacterium
Rhodobacter capsulatus was also investigated by the site-directed
- lkegami, I., Itoh, S., Warren, P.G. and Golbeck, J.H. (1993)
Reconstitution of the photosystem I secondary quinone acceptor (A1) in
the P700-Fx core isolated from Synechococcus PCC6301. Plant Cell Physiol.
- Katoh, T. Tanaka, A. and Mimuro, M. (1993) Isolation of
fucoxanthin-chlorophyll a/c protein assembly from brown algae. In:
Methods in Enzymology, Vol. 214, Packer, R. ed., Academic Press, New York,
- Matsuura, K., Hirota, M., Shimada, K. and Mimuro, M. (1993) Spectral
forms and orientation of bacteriochlorophylls c and a in chlorosomes of
the green photosynthetic bacterium Chloroflex aurantiacus. Photochem.
Photo-biol. 57, 92-97.
- Mimuro, M. (1993) Identification of the terminal energy donor to the
reaction center in the pigment system of green plants by time-resolved
fluorescence spectroscopy at -196C. Plant Cell Physiof 34, 321-327.
- Mimuro, M., Nagashima, U., Nagaoka, S., Takaichi, S., Yamazaki, I.,
Nishimura, Y. and Katoh, T. (1993) Direct detection of a low-lying
singlet excited (2Ag) state of a linear carotenoid, neurosporene, in
solutions. Chem. Phys. Lett 204, 101-105.
- Mimuro, M., Takaichi, S., Yamamoto, Y., Ito, M., Nagaoka, S., Nishimura,
Y., Yamazaki, I., Katoh, T. and Nagashima, U. (1993) The effect of
molecular structure on the relaxation processes in carotenoids containing
a carbonyl group. Chem. Phys. Lett. 213, 576-580.
- Murakami, A. and Fujita, Y. (1993) Regulation of stoichiometry between
PSI and PSII in response to light regime for photosynthesis observed with
Synechocystis PCC 6714: Relationship between redox state of Cyi b6-f
complex and regulation of PSI formation. Plant Cell Physiot 34, 1175-1180.
- Nagashima, K.V.P., Itoh, S., Shimada, K. and Matsuura, K. (1993)
Photooxidation of reaction center-bound cytochrome c and generation of
membrane potential determined by carotenoid band shift in the purple
photosynthetic bacterium, Rhodospirillum molischianum. Biochim. Biophys.
Acta, 1140, 297-303.
- Nagae, H., Kakitani, T., Katoh, T. and Mimuro, M. (1993) A theoretical
study on the interaction between carotenoids and bacteriochlorophyll:
Calculation of the extitation transfer matrix elements between
neurosporene S2 and Sl states and Bchl a S2 and S1 states. J. Chem. Phys.
- Nishimura, Y., Shimada, K., Yamazaki, I. and Mimuro, M. (1993) Energy
transfer processes in Rhodobacter palustris grown under low-light
conditions: Heterogenous composition of LH2 complexes and parallel energy
flow pathways. FEBS Lett. 329, 319-323.
- Oh-oka, H., Kakutani, S., Matsubara, H., Malkin, R. and Itoh, S. (1993)
Isolation of the photoactive reaction center complex that contains three
types of Fe-S centers and a cytochrome c subunit from the green sulfur
bacterium Chlorobium limicola f thiosulfatophilum, strain Larsen. Plant
CellPhysioL 34, 93-101.
- Uehara, K., Hioki, Y. and Mimuro, M. (1993) The chlorophyll a aggregate
absorbing near 685 nm is selectively formed in aqueous tetrahydrofuran.
Photochem. PhotobioL 58, 127-132.
Supplements to 1992
- Aizawa, K. and Fujita, Y. (1992) Regulation of PSI formation induced by
light quality observed with Synechocystis PCC 6714. In Research in
Photosynthesis (Murata, N. ed., Kluwer Academic Publishers, Dordrecht),
Vol. IV, pp. 329-332.
- Fujita, Y., Murakami, A. and Aizawa, K. (1992) Light acclimation of
thylakoid system in cyanophytes: Regulation of PSI formation in response
to light regime. In Research in Photosynthesis (Murata, N. ed., Kluwer
Academic Publishers, Dordrecht), Vol. IV, pp. 301-308.
- Hoshina, S., Sue, S., Wada, K., Enami, I. and Itoh, S. (1992)
Stabilization of iron-sulfur centers A and B in photosystem I particles
by chemical crosslinking. In Research in Photosynthesis (Murata, N. ed.,
Kluwer Academic Publishers, Dordrecht), Vol. I, pp. 581-584.
- Itoh, S., Mimuro, M. and lwaki, M. (1992) Organization of chlorophylls in
photosystem I reaction center: Study by LD and fluorescence measurements
in the ether-extracted particles which contain 11 chlorophyll/P700. In
Research in Photosynthesis (Murata, N. ed., Kluwer Academic Publishers,
Dordrecht), Vol. I, pp. 541-544.
- Iwaki, M., Taksahashi, M., Shimada, K. and Itoh, S. (1992) Identification
of the quinone binding site in PSI reaction center complex by
photoaffinity labeling. In Research in Photosynthesis (Murata, N. ed.,
Kluwer Academic Publishers, Dordrecht) Vol. I, pp. 529-532.
- Katoh, T. and Mimuro, M. (1992) S1 state of fucoxanthin involved in
energy transfer to chlorophyll a in the light harvesting protein of brown
algae. In Research in Photosynthesis (Murata, N. ed., Kluwer Academic
Publishers, Dordrecht) Vol. I, pp. 227-230.
- Kobayashi, M., Van de Meent, E.J., Oh-oka, H., Inoue, K., Itoh, S., Amesz,
J. and Watanabe, T. (1992) Pigment composition of heriobacteria and green
sulfur bacteria. In Research in Photosynthesis (Murata, N. ed., Kluwer
Academic Publishers, Dordrecht), Vol. I, pp. 393-396.
- Matsuura, K., Hirota, M., Shimada, K. and Mimuro, M. (1992) Pigment
orientation and energy transfer kinetics in chlorosomes of green
photosynthetic bacteria. In Research in Photosynthesis (Murata, N. ed.,
Kluwer Academic Publishers, Dordrecht) Vol. 1, pp. 113-116.
- Mimuro, M. (1992) A Iong wavelength antenna in photosynthetic pigment
system. In Research in Photosynthesis. (Murata, N. ed., Kluwer Academic
Publishers, Dordrecht), Vol. 1, pp. 259-262.
- Mimuro, M., Matsuura, K., Nishimura, Y., Shimada, K. and Yamazaki, I.
(1992) Excitation energy transfer processes in green photosynthetic
bacteria: Analysis in picosecond time domain. In Research in
Photosynthesis (Murata, N. ed., Kluwer Academic Publishers, Dordrecht)
Vol. I, pp. 17-24.
- Murakami, A. and Fujita, Y. (1992) In vivo electron transport from Cyt
b6-f complex to photosystem I complex in Synechocystis PCC 6714. In
Research in Photosynthesis (Muratsa, N. ed., Kluwer Academic Publishers,
Dordrecht), Vol. II, pp. 503-506.
- Nakayama, K., Mimuro, M., Nishimura, Y. and Okada, M. (1992) Chlorophyll
forms and excitation energy transfer pathways in light-harvesting
chlorophyll a/b protein complexes from the siphonous green alga Bryopsis
maxima. In Research in Photosynthesis (Murata, N. ed., Kluwer Academic
Publishers, Dordrecht) Vol. I, pp. 219-222.
- Oh-oka, H., Kakutani, S., Itoh, S., Matsubara, H. and Malkin, R. (1992)
Isolation and characterization of the photoactive reaction center complex
from the green sulfur bacterium Chlorobium lumicola. In Research in
Photosynthesis (Murata, N. ed., Kluwer Acsademic Publishers, Dordrecht)
Vol. I, pp. 385-388.
- Ohki, K. and Fujita, Y. (1992) Lightdependent maintenance of active
nitrogenase in the non-heterogenous cyanophyte Trichodesmium sp. NIBB
1067. In Research in Photosynthesis (Murata, N. ed., Kluwer Academic
Publishers) Vol. IV, pp. 103-106.
- Shimada, K., Nishimura, Y., Yamazaki, I. and Mimuro, M. (1992) Excitation
energy flow in Roseobacter denitrificance (Erythrobacter sp. OCh 114) at
low temperature. In Research in Photosynthesis (Murata, N. ed., Kluwer
Academic Publishers, Dordrecht) Vol. I, pp. 137-140.
Last update Oct21, 1994