Redox potential of pheophytin a in photosystem II of two cyanobacteria having the different special pair chlorophylls

Suleyman I. Allakhverdiev, Tatsuya Tomo, Yuichiro Shimada, Hayato Kindo, Ryo Nagao, Vyacheslav V. Klimov, Mamoru Mimuro

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68 Citations (Scopus)

Abstract

Water oxidation by photosystem (PS) II in oxygenic photosynthetic organisms is a major source of energy on the earth, leading to the production of a stable reductant. Mechanisms generating a high oxidation potential for water oxidation have been a major focus of photosynthesis research. This potential has not been estimated directly but has been measured by the redox potential of the primary electron acceptor, pheophytin (Phe) a.However, the reported values for Phe a are still controversial. Here,we measured the redox potential of Phe a under physiological conditions (pH 7.0; 25 °C) in two cyanobacteria with different special pair chlorophylls (Chls): Synechocystis sp. PCC 6803, whose special pair for PS II consists of Chl a, and Acaryochloris marina MBIC 11017, whose special pair for PS II consists of Chl d.We obtained redox potentials of -536 ± 8 mV for Synechocystis sp. PCC 6803 and -478 ± 24 mV for A. marina on PS II complexes in the presence of 1.0 M betaine. The difference in the redox potential of Phe a between the two species closely corresponded with the difference in the light energy absorbed by Chl a versus Chld.We estimated the potentials of the special pair of PS II to be 1.20 V and 1.18 V for Synechocystis sp. PCC 6803 (P680) and A. marina (P713), respectively. This clearly indicates conservation in the properties of water-oxidation systems in oxygenic photosynthetic organisms, irrespective of the special-pair chlorophylls.

Original languageEnglish
Pages (from-to)3924-3929
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume107
Issue number8
DOIs
Publication statusPublished - Feb 23 2010

Keywords

  • Betaine
  • Chlorophyll d
  • Oxygen evolution
  • Photosynthesis
  • Redox titration

ASJC Scopus subject areas

  • General

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