Oct, 2009
Spectroelectrochemical determination of the redox potential of pheophytin a, the primary electron acceptor in photosystem II
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
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- Volume
- 106
- Number
- 41
- First page
- 17365
- Last page
- 17370
- Language
- English
- Publishing type
- Research paper (scientific journal)
- DOI
- 10.1073/pnas.0905388106
- Publisher
- NATL ACAD SCIENCES
Thin-layer cell spectroelectrochemistry, featuring rigorous potential control and rapid redox equilibration within the cell, was used to measure the redox potential E(m)(Phe a/Phe a(-)) of pheophytin (Phe) a, the primary electron acceptor in an oxygen-evolving photosystem (PS) II core complex from a thermophilic cyanobacterium Thermosynechococcus elongatus. Interferences from dissolved O(2) and water reductions were minimized by airtight sealing of the sample cell added with dithionite and mercury plating on the gold minigrid working electrode surface, respectively. The result obtained at a physiological pH of 6.5 was E(m)( Phe a/Phe a(-)) = -505 +/- 6 mV vs. SHE, which is by approximate to 100 mV more positive than the values measured approximate to 30 years ago at nonphysiological pH and widely accepted thereafter in the field of photosynthesis research. Using the P680* - Phe a free energy difference, as estimated from kinetic analyses by previous authors, the present result would locate the E(m)(P680/P680(+)) value, which is one of the key parameters but still resists direct measurements, at approximately +1,210 mV. In view of these pieces of information, a renewed diagram is proposed for the energetics in PS II.
- Link information
- ID information
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- DOI : 10.1073/pnas.0905388106
- ISSN : 0027-8424
- CiNii Articles ID : 80020620399
- Web of Science ID : WOS:000270754400028