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High and low potential forms of the QA quinone electron acceptor in Photosystem II of Thermosynechococcus elongatus and spinach

Paper ID Volume ID Publish Year Pages File Format Full-Text
29621 44425 2011 4 PDF Available
Title
High and low potential forms of the QA quinone electron acceptor in Photosystem II of Thermosynechococcus elongatus and spinach
Abstract

The redox potential of QA in Photosystem II (PSII) from Thermosynechococcus elongatus was titrated monitoring chlorophyll fluorescence. A high potential form (Em = +60 ± 25 mV) was found in the absence of Mn4Ca, the active site for water oxidation. The low potential form (Em = −60 ± 48 mV), which is difficult to measure in conventional titration experiments, could be “locked in” by cross-linking the active enzyme. This indicates that the presence of Mn4Ca is relayed to the quinone site by significant structural changes in the protein. The presence of high and low potential forms agrees with what has been seen in plants, algae from our lab and in T. elongatus (Shibamoto et al., Biochemistry 48 (2009) 10682–10684). In the latter work, the potentials of QA were shifted to lower potentials compared to other measurements. The redox potential of QA in Mn-depleted PSII from spinach was titrated in the presence of redox mediators and the midpoint potential was shifted by 80 mV towards a more negative value compared to titrations without mediators. The lower values of the midpoint potential of the (QA/QA-) redox couple in the literature could be due to a perturbation due to a specific mediator.

Research highlights► QA redox potential (Em) of PSII from T. elongatus was determined. ► Em = +60 ± 25 mV for inactive Mn-depleted PSII. ► Em = −60 ± 48 mV for active, cross-linked PSII. ► The Mn cluster is relayed to the quinone site by signifiant structural changes.

Keywords
Photosystem II; Oxygen evolving enzyme; Quinone redox potential; Chlorophyll fluorescence
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High and low potential forms of the QA quinone electron acceptor in Photosystem II of Thermosynechococcus elongatus and spinach
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Publisher
Database: Elsevier - ScienceDirect
Journal: Journal of Photochemistry and Photobiology B: Biology - Volume 104, Issues 1–2, July–August 2011, Pages 154–157
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Bioengineering
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Don't Miss Today's Special Offer
Price was $35.95
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Price after discount Only $4.95
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