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Silicomolybdate substitutes for the function of a primary electron acceptor and stabilizes charge separation in the photosystem II reaction center complex
Author(s) -
Takahashi Yuichiro,
Satoh Kimiyuki,
Itoh Shigeru
Publication year - 1989
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(89)81076-2
Subject(s) - p680 , chemistry , pheophytin , photochemistry , photosynthetic reaction centre , photosystem ii , electron acceptor , acceptor , p700 , electron donor , electron paramagnetic resonance , photosystem i , electron transfer , nuclear magnetic resonance , photosynthesis , catalysis , organic chemistry , biochemistry , physics , condensed matter physics
Effects of silicomolybdate on the charge recombination between P680 + and the reduced pheophytin were studied by absorption and electron paramagnetic resonance spectroscopies in the photosystem II D1/D2/cytochrome b ‐559 reaction center complex. This preparation lacks the primary and secondary quinone acceptors, Q A and Q B , and exhibits the charge recombination which produces the triplet state of P680 to a large extent. In the presence of silicomolybdate, the light‐induced triplet signal of P680 was almost completely eliminated at cryogenic temperatures as well as at 4°C. Under these conditions, two types of signals, one reversible and the other irreversible, which are ascribable to P680 + and the cation radical of antenna chlorophyll a , respectively, were generated upon illumination at cryogenic temperatures. These results indicate that silicomolybdate, which is known to be an artificial electron acceptor of Q A , rapidly receives electrons from the reduced pheophytin even at cryogenic temperatures and thus suppresses the radical pair recombination which occurs in the time range of nanosecond. P680 + formed by flash excitation in the presence of silicomolybdate relaxed mainly with a long half decay time of 74 ms at 4°C. This indicates that the reduction of P680 + by the secondary electron donor, Z, is significantly decreased.