Jul 27, 2014

Cationic screening of charged surface groups (carboxylates) affects electron transfer steps in photosystem-II water oxidation and quinone reduction

Biochimica Et Biophysica Acta
Oliver KargeHolger Dau

Abstract

The functional or regulatory role of long-distance interactions between protein surface and interior represents an insufficiently understood aspect of protein function. Cationic screening of surface charges determines the morphology of thylakoid membrane stacks. We show that it also influences directly the light-driven reactions in the interior of photosystem II (PSII). After laser-flash excitation of PSII membrane particles from spinach, time courses of the delayed recombination fluorescence (10μs-10ms) and the variable chlorophyll-fluorescence yield (100μs-1s) were recorded in the presence of chloride salts. At low salt-concentrations, a stimulating effect was observed for the S-state transition efficiency, the time constant of O2-formation at the Mn4Ca-complex of PSII, and the halftime of re-oxidation of the primary quinone acceptor (Qa) by the secondary quinone acceptor (Qb). The cation valence determined the half-effect concentrations of the stimulating salt effect, which were around 6μM, 200μM and 10mM for trivalent (LaCl3), bivalent (MgCl2, CaCl2), and monovalent cations (NaCl, KCl), respectively. A depressing high-salt effect also depended strongly on the cation valence (onset concentrations around 2mM, 50mM, and 500mM)...Continue Reading

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References

Mentioned in this Paper

Spinach preparation
Photopsia
Calcium [EPC]
Benzoquinone
Thylakoid Membrane
Entire Lumen of Body System
Calcium
Stroma
Quinones
Complex (molecular entity)

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