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.

Structure, Electron Transfer Chain of Photosystem II and the Mechanism of Water Splitting

2021 ◽  
pp. 3-38
Author(s):  
Jian-Ren Shen ◽  
Yoshiki Nakajima ◽  
Fusamichi Akita ◽  
Michihiro Suga
Keyword(s):  
Electron Transfer ◽  
Photosystem Ii ◽  
Water Splitting ◽  
Electron Transfer Chain ◽  
Transfer Chain

scholarly journals Mediator-assisted water oxidation by the ruthenium “blue dimer” cis,cis-[(bpy)2(H2O)RuORu(OH2)(bpy)2]4+

2008 ◽  
Vol 105 (46) ◽  
pp. 17632-17635 ◽  
Author(s):  
Javier J. Concepcion ◽  
Jonah W. Jurss ◽  
Joseph L. Templeton ◽  
Thomas J. Meyer
Keyword(s):  
Carbon Dioxide ◽  
Electron Transfer ◽  
Renewable Energy ◽  
Photosystem Ii ◽  
Water Splitting ◽  
Water Oxidation ◽  
Oxygenic Photosynthesis ◽  
Reduced Water ◽  
Insight Into ◽  
Recent Insight

Light-driven water oxidation occurs in oxygenic photosynthesis in photosystem II and provides redox equivalents directed to photosystem I, in which carbon dioxide is reduced. Water oxidation is also essential in artificial photosynthesis and solar fuel-forming reactions, such as water splitting into hydrogen and oxygen (2 H2O + 4 hν → O2 + 2 H2) or water reduction of CO2 to methanol (2 H2O + CO2 + 6 hν → CH3OH + 3/2 O2), or hydrocarbons, which could provide clean, renewable energy. The “blue ruthenium dimer,” cis,cis-[(bpy)2(H2O)RuIIIORuIII(OH2)(bpy)2]4+, was the first well characterized molecule to catalyze water oxidation. On the basis of recent insight into the mechanism, we have devised a strategy for enhancing catalytic rates by using kinetically facile electron-transfer mediators. Rate enhancements by factors of up to ≈30 have been obtained, and preliminary electrochemical experiments have demonstrated that mediator-assisted electrocatalytic water oxidation is also attainable.

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.

Photochemical reactions in organized assemblies. 40. Amylose and carboxymethylamylose inclusion complexes with photoreactive molecules

1985 ◽  
Vol 63 (6) ◽  
pp. 1315-1319 ◽  
Author(s):  
Brian R. Suddaby ◽  
Raymond N. Dominey ◽  
Y. Hui ◽  
David G. Whitten
Keyword(s):  
Electron Transfer ◽  
Photochemical Reactions ◽  
Water Soluble ◽  
Enhanced Fluorescence ◽  
Transfer Rates ◽  
Back Electron Transfer ◽  
Organized Assemblies ◽  
Stilbene Derivatives ◽  
Polypyridine Complexes ◽  
Ruthenium Polypyridine

This paper focuses on a study of unimolecular and bimolecular photoreactions occurring with reactants which can be incorporated into the linear polysugars amylose and carboxymethylamylose. Hydrophobic and surfactant trans (E) stilbene derivatives form complexes in which the stilbene chromophore shows enhanced fluorescence and reduced trans → cis isomerization efficiencies. The reactivity of the excited surfactant–stilbene singlet towards the quencher iodide ion has been compared in water/dimethylsulfoxide in the presence and absence of amylose under conditions where complex formation is nearly complete. Some relatively hydrophobic viologen dications have also been found to form complexes with the water soluble carboxymethylamylose. Although the dications complex relatively weakly, the partially reduced monocations complex more strongly. This results in selective retardation of back electron transfer rates when the viologens are used as electron transfer quencher-oxidants for certain luminescent ruthenium polypyridine complexes.

Photosystem II: an enzyme of global significance

2006 ◽  
Vol 34 (5) ◽  
pp. 619-631 ◽  
Author(s):  
J. Barber
Keyword(s):  
Photosystem Ii ◽  
Water Splitting ◽  
Organic Molecules ◽  
Metal Cluster ◽  
Thylakoid Membranes ◽  
Chemical System ◽  
X Ray ◽  
X Ray Crystallography ◽  
Structural Details ◽  
Lipid Environment

Photosystem II (PSII) is a multisubunit enzyme embedded in the lipid environment of the thylakoid membranes of plants, algae and cyanobacteria. Powered by light, this enzyme catalyses the chemically and thermodynamically demanding reaction of water splitting. In so doing, it releases dioxygen into the atmosphere and provides the reducing equivalents required for the conversion of CO2 into the organic molecules of life. Recently, a fully refined structure of a 700 kDa cyanobacterial dimeric PSII complex was elucidated by X-ray crystallography which gave organizational and structural details of the 19 subunits (16 intrinsic and three extrinsic) which make up each monomer and provided information about the position and protein environments of 57 different cofactors. The water-splitting site was revealed as a cluster of four Mn ions and a Ca2+ ion surrounded by amino acid side chains, of which six or seven form direct ligands to the metals. The metal cluster was modelled as a cubane-like structure composed of three Mn ions and the Ca2+ linked by oxo-bonds with the fourth Mn attached to the cubane via one of its oxygens. The overall structure of the catalytic site is providing a framework to develop a mechanistic scheme for the water-splitting process, knowledge which could have significant implications for mimicking the reaction in an artificial chemical system.

Effect of α- and β-cyclodextrins on the photochemical activity of thylakoid membranes and photosystem II particles from barley (Hordeum vulgare): oxygen evolution and whole chain electron transport

2005 ◽  
Vol 83 (3) ◽  
pp. 320-328 ◽  
Author(s):  
S Dudekula ◽  
G Sridharan ◽  
M Fragata
Keyword(s):  
Electron Transfer ◽  
Electron Transport ◽  
Hordeum Vulgare ◽  
Photosystem Ii ◽  
Oxygen Evolution ◽  
Thylakoid Membranes ◽  
Photochemical Activity ◽  
Nonlinear Dependence ◽  
Hordeum Vulgare L ◽  
Sigmoidal Curve

The effect of α- and β-cyclodextrin (CD) concentration (0–16 mM) on oxygen evolution in photosystem II (PSII) and whole chain electron transport (H2O to photosystem I (PSI)) was studied in isolated thylakoid membranes and PSII particles from barley (Hordeum vulgare L.). The CDs are cyclic oligosaccharides containing, for example, six (α-CD) or seven (β-CD) α-D-glucose residues linked by α-1,4 glycosidic bonds. These compounds alter the lipid composition of the thylakoids and most likely also the structure of their membrane proteins. We show for the first time that in the thylakoid membranes, but not in the isolated PSII particles, the relationship between oxygen evolution in PSII and the CD concentration is represented by a S-shaped (sigmoidal) curve displaying a sharp inflexion point or transition. We found, in addition, that the CDs inhibit the whole chain electron transport from H2O to methyl viologen, that is, PSI, measured as oxygen uptake, according to a nonlinear dependence that is also sigmoidal. Moreover, another interesting observation is that in the thylakoid membranes the electron transport from H2O to PSI is quite well inhibited at low CD concentrations (<4–6 mM), whereas the oxygen evolution in PSII is only substantially enhanced at CD concentrations greater than 8–10 mM. To explain this, we suggest that the mechanisms underlying the inhibition of electron transfer from H2O to PSI become operative before those giving origin to the enhancement of oxygen evolution in PSII.Key words: cyclodextrins, electron transfer, nonlinearity, oxygen evolution, photosystem, thylakoid membrane.

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