Abstract
The recent crystallographic structure at 3.0 Å resolution of PSII from Thermosynechococcus elongatus has revealed a cavity in the protein which connects the membrane phase to the binding pocket of the secondary plastoquinone Q B. The cavity may serve as a quinone diffusion pathway. By fluorescence methods, electron transfer at the donor and acceptor sides was investigated in the same membrane-free PSII core particle preparation from T. elongatus prior to and after crystallization; PSII membrane fragments from spinach were studied as a reference. The data suggest selective enrichment of those PSII centers in the crystal that are intact with respect to O 2 evolution at the manganese–calcium complex of water oxidation and with respect to the integrity of the quinone binding site. One and more functional quinone molecules (per PSII monomer) besides of Q A and Q B were found in the crystallized PSII. We propose that the extra quinones are located in the Q B cavity and serve as a PSII intrinsic pool of electron acceptors.
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Schedule a callMore From: Biochimica et Biophysica Acta (BBA) - Bioenergetics
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