Influence of the PsbA1/PsbA3, Ca(2+)/Sr(2+) and Cl(-)/Br(-) exchanges on the redox potential of the primary quinone Q(A) in Photosystem II from Thermosynechococcus elongatus as revealed by spectroelectrochemistry.
Ca(2+) and Cl(-) ions are essential elements for the oxygen evolution activity of photosystem II (PSII). It has been demonstrated that these ions can be exchanged with Sr(2+) and Br(-), respectively, and that these ion exchanges modify the kinetics of some electron transfer reactions at the Mn₄Ca cluster level (Ishida et al., J. Biol. Chem. 283 (2008) 13330-13340). It has been proposed from thermoluminescence experiments that the kinetic effects arise, at least in part, from a decrease in the free energy level of the Mn(4)Ca cluster in the S₃ state though some changes on the acceptor side were also observed. Therefore, in the present work, by using thin-layer cell spectroelectrochemistry, the effects of the Ca(2+)/Sr(2+) and Cl(-)/Br(-) exchanges on the redox potential of the primary quinone electron acceptor Q(A), E(m)(Q(A)/Q(A)(-)), were investigated. Since the previous studies on the Ca(2+)/Sr(2+) and Cl(-)/Br(-) exchanges were performed in PsbA3-containing PSII purified from the thermophilic cyanobacterium Thermosynechococcus elongatus, we first investigated the influences of the PsbA1/PsbA3 exchange on E(m)(Q(A)/Q(A)(-)). Here we show that i) the E(m)(Q(A)/Q(A)(-)) was up-shifted by ca. +38mV in PsbA3-PSII when compared to PsbA1-PSII and ii) the Ca(2+)/Sr(2+) exchange up-shifted the E(m)(Q(A)/Q(A)(-)) by ca. +27mV, whereas the Cl(-)/Br(-) exchange hardly influenced E(m)(Q(A)/Q(A)(-)). On the basis of the results of E(m)(Q(A)/Q(A)(-)) together with previous thermoluminescence measurements, the ion-exchange effects on the energetics in PSII are discussed.
Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan. yuki.kato@bio.phys.nagoya-u.ac.jp
Yuki
Y
Kato
Tadao
T
Shibamoto
Shoichi
S
Yamamoto
Tadashi
T
Watanabe
Naoko
N
Ishida
Miwa
M
Sugiura
Fabrice
F
Rappaport
Alain
A
Boussac
D001965:Bromides / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism*; D055664:Electrochemical Techniques; D004579:Electron Transport; D010084:Oxidation-Reduction; D045332:Photosystem II Protein Complex / Q000502:physiology*; D011809:Quinones / Q000737:chemistry*; D013324:Strontium / Q000378:metabolism*; D046940:Synechococcus / Q000378:metabolism*
D001965:Bromides; D002712:Chlorides; D045332:Photosystem II Protein Complex; D011809:Quinones; C422369:photosystem II, psbA subunit; D002118:Calcium; D013324:Strontium