Silicomolybdate substitutes for the function of a primary electron acceptor and stabilizes charge separation in the photosystem II reaction center complex

Yuichiro Takahashi, Kimiyuki Satoh, Shigeru Itoh

Research output: Contribution to journalArticle

22 Citations (Scopus)

Abstract

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, QA and QB, 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 QA, 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.

Original languageEnglish
Pages (from-to)133-138
Number of pages6
JournalFEBS Letters
Volume255
Issue number1
DOIs
Publication statusPublished - Sep 11 1989

Fingerprint

Photosystem II Protein Complex
Pheophytins
Electrons
Cryogenics
Genetic Recombination
Temperature
Electron Spin Resonance Spectroscopy
Lighting
Paramagnetic resonance
Cations
Spectrum Analysis
Spectroscopy
Antennas
Light
silicomolybdate

Keywords

  • Photosynthesis
  • Photosystem II
  • Radical pair recombination
  • Reaction center
  • Silicomolybdate
  • Triplet state

ASJC Scopus subject areas

  • Biochemistry
  • Biophysics
  • Molecular Biology

Cite this

Silicomolybdate substitutes for the function of a primary electron acceptor and stabilizes charge separation in the photosystem II reaction center complex. / Takahashi, Yuichiro; Satoh, Kimiyuki; Itoh, Shigeru.

In: FEBS Letters, Vol. 255, No. 1, 11.09.1989, p. 133-138.

Research output: Contribution to journalArticle

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AB - 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, QA and QB, 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 QA, 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.

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