Determination of the Miss Probabilities of Individual S-State Transitions during Photosynthetic Water Oxidation by Monitoring Electron Flow in Photosystem II Using FTIR Spectroscopy

Biochemistry ◽  
2012 ◽  
Vol 51 (34) ◽  
pp. 6776-6785 ◽  
Author(s):  
Hiroyuki Suzuki ◽  
Miwa Sugiura ◽  
Takumi Noguchi
Keyword(s):  
Photosystem Ii ◽  
Ftir Spectroscopy ◽  
Water Oxidation ◽  
Electron Flow ◽  
State Transitions ◽  
Photosynthetic Water Oxidation

Effect of Magnesium and Calcium Ions on the Photoelectron Transport Activity of Low-Salt Suspended Hydrilla verticillata Thylakoids: Possible Sites of Cation Interaction

1998 ◽  
Vol 53 (9-10) ◽  
pp. 849-856
Author(s):  
Sujata R. Mishra ◽  
Surendra Chandra Sabat
Keyword(s):  
Electron Transport ◽  
Photosystem Ii ◽  
Electron Donor ◽  
Water Oxidation ◽  
Electron Flow ◽  
Hydrilla Verticillata ◽  
Transport Activity ◽  
Low Salt ◽  
Electron Transport Activity ◽  
Stimulation Of

Stimulatory effect of divalent cations like calcium (Ca2+) and magnesium (Mg2+) was investigated on electron transport activity of divalent cation deficient low-salt suspended (LS) thylakoid preparation from a submerged aquatic angiosperm, Hydrilla verticillata. Both the cations stimulated electron transport activity of LS-suspended thylakoids having an intact water oxidation complex. But in hydroxylamine (NH2OH) - or alkaline Tris - washed thylakoid preparations (with the water oxidation enzyme impaired), only Ca2+ dependent stimulation of electron transport activity was found. The apparent Km of Ca2+ dependent stimulation of electron flow from H2O (endogenous) or from artificial electron donor (exogenous) to dichlorophenol indophenol (acceptor) was found to be identical. Calcium supported stimulation of electron transport activity in NH2OH - or Tris - washed thylakoids was electron donor selective, i.e., Ca2+ ion was only effective in electron flow with diphenylcarbazide but not with NH2OH as electron donor to photosystem II. A magnesium effect was observed in thylakoids having an intact water oxidation complex and the ion became unacceptable in NH2OH - or Tris - washed thylakoids. Indirect experimental evidences have been presented to suggest that Mg2+ interacts with the water oxidation complex, while the Ca2+ interaction is localized betw een Yz and reaction center of photosystem II.

scholarly journals Electron, proton and hydrogen–atom transfers in photosynthetic water oxidation

2002 ◽  
Vol 357 (1426) ◽  
pp. 1383-1394 ◽  
Author(s):  
Cecilia Tommos
Keyword(s):  
Photosystem Ii ◽  
Proton Transfer ◽  
Water Oxidation ◽  
Oxidation Mechanism ◽  
Bulk Solution ◽  
Hydrogen Atoms ◽  
Redox Active ◽  
Hydrogen Atom Transfers ◽  
Reduce Carbon Dioxide ◽  
Photosynthetic Water Oxidation

When photosynthetic organisms developed so that they could use water as an electron source to reduce carbon dioxide, the stage was set for efficient proliferation. Algae and plants spread globally and provided the foundation for our atmosphere and for O 2 –based chemistry in biological systems. Light–driven water oxidation is catalysed by photosystem II, the active site of which contains a redox–active tyrosine denoted Y Z , a tetramanganese cluster, calcium and chloride. In 1995, Gerald Babcock and co–workers presented the hypothesis that photosynthetic water oxidation occurs as a metallo–radical catalysed process. In this model, the oxidized tyrosine radical is generated by coupled proton/electron transfer and re–reduced by abstracting hydrogen atoms from substrate water or hydroxide–ligated to the manganese cluster. The proposed function of Y Z requires proton transfer from the tyrosine site upon oxidation. The oxidation mechanism of Y Z in an inhibited and O 2 –evolving photosystem II is discussed. Domino–deprotonation from Y Z to the bulk solution is shown to be consistent with a variety of data obtained on metal–depleted samples. Experimental data that suggest that the oxidation of Y Z in O 2 –evolving samples is coupled to proton transfer in a hydrogen–bonding network are described. Finally, a dielectric–dependent model for the proton release that is associated with the catalytic cycle of photosystem II is discussed.

scholarly journals FTIR detection of water reactions in the oxygen-evolving centre of photosystem II

2007 ◽  
Vol 363 (1494) ◽  
pp. 1189-1195 ◽  
Author(s):  
Takumi Noguchi
Keyword(s):  
Photosystem Ii ◽  
Water Oxidation ◽  
State Transitions ◽  
Proton Release ◽  
Difference Spectra ◽  
Band Shift ◽  
Bonding Structure ◽  
Ph Dependency ◽  
Ftir Difference Spectroscopy ◽  
Oxygen Evolving

Flash-induced Fourier transform infrared (FTIR) difference spectroscopy has been used to study the water-oxidizing reactions in the oxygen-evolving centre of photosystem II. Reactions of water molecules were directly monitored by detecting the OH stretching bands of weakly H-bonded OH of water in the 3700–3500 cm −1 region in FTIR difference spectra during S-state cycling. In the S 1 →S 2 transition, a band shift from 3588 to 3617 cm −1 was observed, indicative of a weakened H-bond. Decoupling experiments using D 2 O : H 2 O (1 : 1) showed that this OH arose from a water molecule with an asymmetric H-bonding structure and this asymmetry became more significant upon S 2 formation. In the S 2 →S 3 , S 3 →S 0 and S 0 →S 1 transitions, negative bands were observed at 3634, 3621 and 3612 cm −1 , respectively, representing formation of a strong H-bond or a proton release reaction. In addition, using complex spectral features in the carboxylate stretching region (1600–1300 cm −1 ) as ‘fingerprints’ of individual S-state transitions, pH dependency of the transition efficiencies and the effect of dehydration were examined to obtain the information of proton release and water insertion steps in the S-state cycle. Low-pH inhibition of the S 2 →S 3 , S 3 →S 0 and S 0 →S 1 transitions was consistent with a view that protons are released in the three transitions other than S 1 →S 2 , while relatively high susceptibility to dehydration in the S 2 →S 3 and S 3 →S 0 transitions suggested the insertion of substrate water into the system during these transitions. Thus, a possible mechanism of water oxidation to explain the FTIR data is proposed.

scholarly journals Fast enzymatic HCO3- dehydration supports photosynthetic water oxidation in Photosystem II from pea

2021 ◽  
Author(s):  
Alexandr V. Shitov ◽  
Vasily V. Terentyev ◽  
Govindjee Govindjee
Keyword(s):  
Photosystem Ii ◽  
Pisum Sativum ◽  
Water Oxidation ◽  
Photochemical Reactions ◽  
O2 Evolution ◽  
Donor Side ◽  
Psii Photochemistry ◽  
Similar Dependence ◽  
Enzymatic Nature ◽  
Photosynthetic Water Oxidation

Carbonic anhydrase (CA) activity, associated with Photosystem II (PSII) from Pisum sativum, has been shown to enhance water oxidation. But, the nature of the CA activity, its origin and role in photochemistry has been under debate, since the rates of CA reactions, measured earlier, were less than the rates of photochemical reactions. Here, we demonstrate high CA activity in PSII from Pisum sativum, measured by HCO3- dehydration at pH 6.5 (i.e. under optimal condition for PSII photochemistry), with kinetic parameters Km of 2.7 mM; Vmax of 2.74·10-2 mM·sec-1; kcat of 1.16·103 sec-1 and kcat/Km of 4.1·105 M-1 sec-1, showing the enzymatic nature of this activity, which kcat exceeds by ~13 times the rate of PSII, as measured by O2 evolution. The similar dependence of HCO3- dehydration, of the maximal quantum yield of photochemical reactions and of O2 evolution on the ratio of chlorophyll/photochemical reaction center II demonstrate the interconnection of these processes on the electron donor side of PSII. Since the removal of protons is critical for fast water oxidation, and since HCO3- dehydration consumes a proton, we suggest that CA activity, catalyzing very fast removal of protons, supports efficient water oxidation in PSII and, thus, photosynthesis in general.

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