scholarly journals Metal oxidation states in biological water splitting

2015 ◽  
Vol 6 (3) ◽  
pp. 1676-1695 ◽  
Author(s):  
Vera Krewald ◽  
Marius Retegan ◽  
Nicholas Cox ◽  
Johannes Messinger ◽  
Wolfgang Lubitz ◽  
...  
Keyword(s):  
Photosystem Ii ◽  
Water Splitting ◽  
Oxidation States ◽  
Oxygen Evolving Complex ◽  
Central Question ◽  
Manganese Ions ◽  
Metal Oxidation ◽  
Biological Water ◽  
Oxygen Evolving

A central question in biological water splitting concerns the oxidation states of the manganese ions that comprise the oxygen-evolving complex of photosystem II.

scholarly journals Refined Model of the Oxidation States and Structures of the Mn/Ca/Cl Cluster of the Oxygen Evolving Complex of Photosystem II

1998 ◽  
pp. 1273-1278 ◽  
Author(s):  
Roehl M. Cinco ◽  
Carmen Fernandez ◽  
Johannes Messinger ◽  
John H. Robblee ◽  
Henk Visser ◽  
...  
Keyword(s):  
Photosystem Ii ◽  
Oxidation States ◽  
Oxygen Evolving Complex ◽  
Refined Model ◽  
Oxygen Evolving

Mn K-Edge XANES and Kβ XES Studies of Two Mn−Oxo Binuclear Complexes:  Investigation of Three Different Oxidation States Relevant to the Oxygen-Evolving Complex of Photosystem II

2001 ◽  
Vol 123 (29) ◽  
pp. 7031-7039 ◽  
Author(s):  
Hendrik Visser ◽  
Elodie Anxolabéhère-Mallart ◽  
Uwe Bergmann ◽  
Pieter Glatzel ◽  
John H. Robblee ◽  
...  
Keyword(s):  
Photosystem Ii ◽  
Oxidation States ◽  
Oxygen Evolving Complex ◽  
Binuclear Complexes ◽  
Oxygen Evolving

Electron donation to photosystem II by diphenylcarbazide is inhibited both by the endogenous manganese complex and by exogenous manganese ions

1995 ◽  
Vol 73 (5-6) ◽  
pp. 241-245 ◽  
Author(s):  
Abdur Rashid ◽  
Radovan Popovic
Keyword(s):  
Photosystem Ii ◽  
Antagonistic Effect ◽  
Oxygen Evolving Complex ◽  
Manganese Ions ◽  
Extrinsic Polypeptides ◽  
Negative Role ◽  
Mn Cluster ◽  
Oxygen Evolving ◽  
Electron Donation

Diphenylcarbazide (DPC) is an efficient electron donor to the inactive oxygen-evolving complex of photosystem II (PSII). We investigated the role of manganese on the rate of electron donation from DPC to PSII in both Mn-depleted (Tris washed) and Mn-retaining (NaCl washed) PSII preparations. The rate of electron donation from DPC to PSII was significantly higher in Mn-depleted than in Mn-retaining preparations, indicating a negative role of native Mn complex on DPC electron donation. The apparent Km values for DPC were found to be 0.11 and 0.17 mM for Mn-depleted and Mn-retaining PSII preparations, respectively. This difference in the Km values also indicates an antagonistic effect of endogenous Mn cluster on electron donation from DPC, which was markedly inhibited by exogenous Mn2+. However, the magnitude of inhibition was greater in Mn-depleted than in Mn-retaining PSII preparations. This indicates a higher accessibility of DPC to PSII in the absence of native Mn complex. Our results suggest (i) that Mn, either endogenous or added, acts as an accessibility barrier for DPC to donate electrons to PSII and (ii) that the native Mn complex not only functions as an accumulator of oxidizing equivalents but may also protect PSII from exogenous reductants.Key words: photosystem II, extrinsic polypeptides, Mn complex, electron transport, diphenylcarbazide.

‘Photosystem II: the water splitting enzyme of photosynthesis and the origin of oxygen in our atmosphere’

2016 ◽  
Vol 49 ◽  
Author(s):  
James Barber
Keyword(s):  
Photosystem Ii ◽  
Water Splitting ◽  
Water Oxidation ◽  
18Th Century ◽  
Metal Cluster ◽  
Oxygen Evolving Complex ◽  
Structural Details ◽  
Unlimited Supply ◽  
Lipid Environment ◽  
Oxygen Evolving

AbstractAbout 3 billion years ago an enzyme emerged which would dramatically change the chemical composition of our planet and set in motion an unprecedented explosion in biological activity. This enzyme used solar energy to power the thermodynamically and chemically demanding reaction of water splitting. In so doing it provided biology with an unlimited supply of reducing equivalents needed to convert carbon dioxide into the organic molecules of life while at the same time produced oxygen to transform our planetary atmosphere from an anaerobic to an aerobic state. The enzyme which facilitates this reaction and therefore underpins virtually all life on our planet is known as Photosystem II (PSII). It is a pigment-binding, multisubunit protein complex embedded in the lipid environment of the thylakoid membranes of plants, algae and cyanobacteria. Today we have detailed understanding of the structure and functioning of this key and unique enzyme. The journey to this level of knowledge can be traced back to the discovery of oxygen itself in the 18th-century. Since then there has been a sequence of mile stone discoveries which makes a fascinating story, stretching over 200 years. But it is the last few years that have provided the level of detail necessary to reveal the chemistry of water oxidation and O–O bond formation. In particular, the crystal structure of the isolated PSII enzyme has been reported with ever increasing improvement in resolution. Thus the organisational and structural details of its many subunits and cofactors are now well understood. The water splitting site was revealed as a cluster of four Mn ions and a Ca ion surrounded by amino-acid side chains, of which seven provide direct ligands to the metals. The metal cluster is organised as a cubane structure composed of three Mn ions and a Ca2+ linked by oxo-bonds with the fourth Mn ion attached to the cubane. This structure has now been synthesised in a non-protein environment suggesting that it is a totally inorganic precursor for the evolution of the photosynthetic oxygen-evolving complex. In summary, the overall structure of the catalytic site has given a framework on which to build a mechanistic scheme for photosynthetic dioxygen generation and at the same time provide a blue-print and incentive to develop catalysts for artificial photo-electrochemical systems to split water and generate renewable solar fuels.

scholarly journals Assessment of the manganese cluster’s oxidation state via photoactivation of photosystem II microcrystals

2019 ◽  
Vol 117 (1) ◽  
pp. 141-145 ◽  
Author(s):  
Mun Hon Cheah ◽  
Miao Zhang ◽  
Dmitry Shevela ◽  
Fikret Mamedov ◽  
Athina Zouni ◽  
...  
Keyword(s):  
Photosystem Ii ◽  
Oxidation State ◽  
Water Oxidation ◽  
Oxidation States ◽  
Nanosecond Laser ◽  
Paramagnetic Resonance ◽  
Manganese Removal ◽  
Biological Water ◽  
Spectroscopy Studies ◽  
Oxygen Evolving

Knowledge of the manganese oxidation states of the oxygen-evolving Mn4CaO5cluster in photosystem II (PSII) is crucial toward understanding the mechanism of biological water oxidation. There is a 4 decade long debate on this topic that historically originates from the observation of a multiline electron paramagnetic resonance (EPR) signal with effective total spin of S = 1/2 in the singly oxidized S2state of this cluster. This signal implies an overall oxidation state of either Mn(III)3Mn(IV) or Mn(III)Mn(IV)3for the S2state. These 2 competing assignments are commonly known as “low oxidation (LO)” and “high oxidation (HO)” models of the Mn4CaO5cluster. Recent advanced EPR and Mn K-edge X-ray spectroscopy studies converge upon the HO model. However, doubts about these assignments have been voiced, fueled especially by studies counting the number of flash-driven electron removals required for the assembly of an active Mn4CaO5cluster starting from Mn(II) and Mn-free PSII. This process, known as photoactivation, appeared to support the LO model since the first oxygen is reported to evolve already after 7 flashes. In this study, we improved the quantum yield and sensitivity of the photoactivation experiment by employing PSII microcrystals that retained all protein subunits after complete manganese removal and by oxygen detection via a custom built thin-layer cell connected to a membrane inlet mass spectrometer. We demonstrate that 9 flashes by a nanosecond laser are required for the production of the first oxygen, which proves that the HO model provides the correct description of the Mn4CaO5cluster’s oxidation states.

Towards models of the oxygen-evolving complex (OEC) of photosystem II: a Mn4Ca cluster of relevance to low oxidation states of the OEC

2011 ◽  
Vol 47 (39) ◽  
pp. 11128 ◽  
Author(s):  
Evangelia S. Koumousi ◽  
Shreya Mukherjee ◽  
Christine M. Beavers ◽  
Simon J. Teat ◽  
George Christou ◽  
...  
Keyword(s):  
Photosystem Ii ◽  
Oxidation States ◽  
Oxygen Evolving Complex ◽  
Oxygen Evolving
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