Identification of the special pair of photosystem II in a chlorophyll d-dominated cyanobacterium.
The composition of photosystem II (PSII) in the chlorophyll (Chl) d-dominated cyanobacterium Acaryochloris marina MBIC 11017 was investigated to enhance the general understanding of the energetics of the PSII reaction center. We first purified photochemically active complexes consisting of a 47-kDa Chl protein (CP47), CP43' (PcbC), D1, D2, cytochrome b(559), PsbI, and a small polypeptide. The pigment composition per two pheophytin (Phe) a molecules was 55 +/- 7 Chl d, 3.0 +/- 0.4 Chl a, 17 +/- 3 alpha-carotene, and 1.4 +/- 0.2 plastoquinone-9. The special pair was detected by a reversible absorption change at 713 nm (P713) together with a cation radical band at 842 nm. FTIR difference spectra of the specific bands of a 3-formyl group allowed assignment of the special pair. The combined results indicate that the special pair comprises a Chl d homodimer. The primary electron acceptor was shown by photoaccumulation to be Phe a, and its potential was shifted to a higher value than that in the Chl a/Phe a system. The overall energetics of PSII in the Chl d system are adjusted to changes in the redox potentials, with P713 as the special pair using a lower light energy at 713 nm. Taking into account the reported downward shift in the potential of the special pair of photosystem I (P740) in A. marina, our findings lend support to the idea that changes in photosynthetic pigments combine with a modification of the redox potentials of electron transfer components to give rise to an energetic adjustment of the total reaction system.
Tomo
Tatsuya
T
Department of Technology and Ecology, Hall of Global Environmental Research, Kyoto University, Kyoto 606-8501, Japan.
Okubo
Tatsunori
T
Akimoto
Seiji
S
Yokono
Makio
M
Miyashita
Hideaki
H
Tsuchiya
Tohru
T
Noguchi
Takumi
T
Mimuro
Mamoru
M
D002734:Chlorophyll / Q000378:metabolism*; D003067:Coenzymes; D000458:Cyanobacteria / Q000378:metabolism*; D004583:Electrons; D004591:Electrophoresis, Polyacrylamide Gel; D010084:Oxidation-Reduction; D010777:Photochemistry; D045332:Photosystem II Protein Complex / Q000302:isolation & purification / Q000378:metabolism*; D010860:Pigments, Biological / Q000737:chemistry; D021122:Protein Subunits / Q000302:isolation & purification / Q000378:metabolism; D013050:Spectrometry, Fluorescence
D003067:Coenzymes; D045332:Photosystem II Protein Complex; D010860:Pigments, Biological; D021122:Protein Subunits; D002734:Chlorophyll; C107509:chlorophyll d