scholarly journals Redox tuning in biological electron transfer: The role of bicarbonate in Photosystem II

2016 ◽  
Vol 1857 ◽  
pp. e17
Author(s):  
A. William Rutherford ◽  
K. Brinkert ◽  
S. de Causmaecker ◽  
A. Krieger-Lizskay ◽  
A. Fantuzzi
Keyword(s):  
Electron Transfer ◽  
Photosystem Ii ◽  
Redox Tuning ◽  
Biological Electron Transfer

Role of conducting polymeric interfaces in promoting biological electron transfer

1997 ◽  
Vol 12 (8) ◽  
pp. 721-727 ◽  
Author(s):  
Karl S. Ryder ◽  
David G. Morris ◽  
Jonathan M. Cooper
Keyword(s):  
Electron Transfer ◽  
Biological Electron Transfer

scholarly journals Bicarbonate-induced redox tuning in Photosystem II for regulation and protection

2016 ◽  
Vol 113 (43) ◽  
pp. 12144-12149 ◽  
Author(s):  
Katharina Brinkert ◽  
Sven De Causmaecker ◽  
Anja Krieger-Liszkay ◽  
Andrea Fantuzzi ◽  
A. William Rutherford
Keyword(s):  
Electron Transfer ◽  
Photosystem Ii ◽  
Redox State ◽  
Feedback Mechanism ◽  
Back Reaction ◽  
Reaction Route ◽  
Midpoint Potential ◽  
Tuning Mechanism ◽  
Redox Tuning ◽  
The One

The midpoint potential (Em) of QA/QA−•, the one-electron acceptor quinone of Photosystem II (PSII), provides the thermodynamic reference for calibrating PSII bioenergetics. Uncertainty exists in the literature, with two values differing by ∼80 mV. Here, we have resolved this discrepancy by using spectroelectrochemistry on plant PSII-enriched membranes. Removal of bicarbonate (HCO3−) shifts the Em from ∼−145 mV to −70 mV. The higher values reported earlier are attributed to the loss of HCO3− during the titrations (pH 6.5, stirred under argon gassing). These findings mean that HCO3− binds less strongly when QA−• is present. Light-induced QA−• formation triggered HCO3− loss as manifest by the slowed electron transfer and the upshift in the Em of QA. HCO3−-depleted PSII also showed diminished light-induced 1O2 formation. This finding is consistent with a model in which the increase in the Em of QA/QA−• promotes safe, direct P+•QA−• charge recombination at the expense of the damaging back-reaction route that involves chlorophyll triplet-mediated 1O2 formation [Johnson GN, et al. (1995) Biochim Biophys Acta 1229:202–207]. These findings provide a redox tuning mechanism, in which the interdependence of the redox state of QA and the binding by HCO3− regulates and protects PSII. The potential for a sink (CO2) to source (PSII) feedback mechanism is discussed.

scholarly journals The role of TyrD in the electron transfer kinetics in Photosystem II

2008 ◽  
Vol 1777 (12) ◽  
pp. 1510-1517 ◽  
Author(s):  
Malwina Szczepaniak ◽  
Miwa Sugiura ◽  
Alfred R. Holzwarth
Keyword(s):  
Electron Transfer ◽  
Photosystem Ii ◽  
Electron Transfer Kinetics

scholarly journals Bicarbonate Activation of Monomeric Photosystem II-PsbS/Psb27 Complex

2022 ◽  
Author(s):  
A. William Rutherford ◽  
Andrea Fantuzzi ◽  
Dario Piano ◽  
Patrycja Haniewicz ◽  
Domenica Farci ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Photosystem Ii ◽  
Water Splitting ◽  
Thylakoid Membranes ◽  
Protective Mechanism ◽  
Slow Electron ◽  
Enhanced Fluorescence ◽  
Transfer Rates ◽  
Redox Tuning ◽  
In Transit

In thylakoid membranes, Photosystem II monomers from the stromal lamellae contain the subunits PsbS and Psb27 (PSIIm-S/27), while Photosystem II monomers from granal regions (PSIIm) lack these subunits. Here, we have isolated and characterised these two types of Photosystem II complexes. The PSIIm-S/27 showed enhanced fluorescence, the near-absence of oxygen evolution, as well as limited and slow electron transfer from QA to QB compared to the near-normal activities in the granal PSIIm. However, when bicarbonate was added to the PSIIm-S/27, water splitting and QA to QB electron transfer rates were comparable to those in granal PSIIm. The findings suggest that the binding of PsbS and/or Psb27 inhibits forward electron transfer and lowers the binding affinity for the bicarbonate. This can be rationalized in terms of the recently discovered photoprotection role played by bicarbonate binding via the redox tuning of the QA/QA?- couple, which controls the charge recombination route, and this limits chlorophyll triplet mediated 1O2 formation (Brinkert K et al. (2016) Proc Natl Acad Sci U S A. 113(43):12144-12149). These findings suggest that PSIIm-S/27 is an intermediate in the assembly of PSII in which PsbS and/or Psb27 restrict PSII activity while in transit, by using a bicarbonate-mediated switch and protective mechanism.

scholarly journals PGR5 is required for efficient Q cycle in the cytochrome b6f complex during cyclic electron flow

2019 ◽  
Author(s):  
Felix Buchert ◽  
Laura Mosebach ◽  
Philipp Gäbelein ◽  
Michael Hippler
Keyword(s):  
Electron Transfer ◽  
Reductase Activity ◽  
Electron Flow ◽  
Cyclic Electron Flow ◽  
Redox Activity ◽  
Q Cycle ◽  
Redox Tuning ◽  
Photosynthetic Control ◽  
Photosynthetic Electron Transfer

AbstractProton Gradient Regulation 5 (PGR5) is involved in the control of photosynthetic electron transfer but its mechanistic role is not yet clear. Several models have been proposed to explain phenotypes such as a diminished steady state proton motive force (pmf) and increased photodamage of photosystem I (PSI). Playing a regulatory role in cyclic electron flow (CEF) around PSI, PGR5 contributes indirectly to PSI protection by enhancing photosynthetic control, which is a pH-dependent downregulation of electron transfer at the cytochrome b6f complex (b6f). Here, we re-evaluated the role of PGR5 in the green alga Chlamydomonas reinhardtii and conclude that pgr5 possesses a dysfunctional b6f. Our data indicate that the b6f low-potential chain redox activity likely operated in two distinct modes – via the canonical Q cycle during linear electron flow and via an alternative Q cycle during CEF, attributing a ferredoxin-plastoquinone reductase activity to the b6f. The latter mode allowed efficient oxidation of the low-potential chain in the WT b6f. A switch between the two Q cycle modes was dependent of PGR5 and relied on unknown stromal electron carrier(s), which were a general requirement for b6f activity. In CEF-favouring conditions the electron transfer bottleneck in pgr5 was the b6f and insufficient flexibility in the low-potential chain redox tuning might account for the mutant pmf phenotype and the secondary consequences. Models of our findings are discussed.

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