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pH‐Dependent Extraction of Ca 2+ from Photosystem II Membranes and Thylakoid Membranes: Indication of a Ca 2+‐Sensitive Site on the Acceptor Side of Photosystem II
Author(s) -
Semin Boris K.,
Ivanov Llja I.,
Rubin Andrei B.,
Carpentier Robert
Publication year - 1998
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1998.tb02511.x
Subject(s) - photosystem ii , membrane , thylakoid , chemistry , electron acceptor , electron transport chain , dcmu , kinetics , biophysics , f atpase , photochemistry , photosynthesis , chloroplast , biochemistry , biology , physics , quantum mechanics , gene
Abstract The action of low pH treatment (pH 3.6) known to release Ca 2+ from the oxygen‐evolving complex in photosystem II (PSII) membranes and to induce Ca 2+ ‐revers‐ible inhibition of electron transport at the acceptor side of PSII in thylakoid membranes (TM) was compared in PSII membranes and TM. The rate of the inactivation of electron transport by low pH was four times higher in TM than in PSII membranes. Ferricyanide accelerated the inactivation of PSII membranes but decreased it in the case of TM. Low pH treatment also greatly modified the fluorescence induction kinetics in both preparations, but significant differences have been found in the fluorescence induction kinetics of treated TM and PSII membranes. Calcium restored the electron transport activity and fluorescence induction kinetics in PSII membranes and TM, whereas diphenylcarbazide restored these functions only in PSII membranes. The reactivation of Ca‐depleted PSII membranes was more effective in the dark, whereas the reactivation of TM required weak light. In the case of PSII membranes subjected to low pH citrate buffer, maximal reactivation was observed at 60 mM Ca 2+ but for TM about 10 mM Ca 2+ was required and 60 mM fully inhibited electron transport in TM during reactivation. These results indicate that the Ca‐dependent inactivation of the acceptor side of PSII in TM after low pH treatment cannot be explained by the extraction of Ca 2+ from the oxygen‐evolving complex. It is rather suggested that the Ca 2+ involved in this inhibition is bound to the acceptor side of the photosystem near to the Q A ‐non‐heme iron binding site and may participate in the binding of a polypeptide of the PSII light antenna complex to the PSII reaction center.