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Shinkarev, Vladimir P.; Xu, Chunhe; Wraight, Colin A.

doi:10.1023/a:1005721910729

Cited by 24 publications

(5 citation statements)

References 36 publications

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“…The period four oscillation pattern has minima after the third and the seventh flashes at short times ( t < 700 μs) and after the fourth and the eighth flashes at longer times ( t > 700 μs). By using pump and probe fluorometry ( , ) and fast repetition rate fluorometry (), earlier investigators showed the same modulation pattern of the fluorescence yield in thylakoids. For measurements of the fluorescence relaxation kinetics as a function of flash number in PSII membranes, 0.7 μM DCBQ was added to the assay medium.…”

Section: Resultsmentioning

confidence: 79%

“…Oxygen, another known quencher of fluorescence, has also been proposed to contribute to period four oscillations in fluorescence yield (19). However, oxygen does not yet appear at 100 µs after excitation, even though period four oscillations do, and oxygen reaches equilibration between its concentration in local and bulk phases in a few milliseconds (50) so could not explain the persistence of period four oscillations at longer times.…”

Section: Discussionmentioning

confidence: 99%

“…In all previous works fluorescence yields have been studied at certain fixed time delays after excitation flashes. Recently Shinkarev et al (19) attempted to extract more information about the nature of a period four modulation of the Chl a fluorescence by analyzing its decay in a time interval from 70 µs to 50 ms. Their study revealed the presence of a quencher of the Chl a fluorescence arising with a delay of approximately 0.5 ms after excitation. Flash-number dependent changes in the amount of this quencher were characterized by a periodicity of four, with maxima after the third and the seventh flashes.…”

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confidence: 99%

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Modulation of Flash-Induced Photosystem II Fluorescence by Events Occurring at the Water Oxidizing Complex

1999

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The mechanism of flash-induced changes with a periodicity of four in photosystem II (PSII) fluorescence was investigated with the aim of further using fluorescence measurements as an approach to studying the structural and functional organization of the water-oxidizing complex (WOC). The decay of the flash-induced high fluorescence state of PSII was measured with pulse amplitude modulated fluorometry in thylakoids and PSII enriched membrane fragments. Calculated QA- decay was well described by three exponential decay components, reflecting QA- reoxidation with halftimes of 450 and 860 micros, 2 and 7.6 ms, and 111 and 135 ms in thylakoids and PSII membranes, respectively. The effect of modification of the PSII donor side by changing pH or by removal of the extrinsic 17 and 24 kDa proteins on period four oscillations in both maximum fluorescence yield and the relative contribution of QA- reoxidation reactions was compared to flash-induced oxygen yield. The four-step oxidation of the manganese cluster of the WOC was found to be necessary but not sufficient to produce modulation of PSII fluorescence. The capacity of the WOC to generate molecular oxygen was also required to observe a period four in the fluorescence; however, direct quenching by oxygen was not responsible for the modulation. Potential mechanisms responsible for the periodicity of four in both maximum fluorescence yield pattern and flash-dependent changes in proportion of centers with different QA- reoxidation rates are discussed with respect to intrinsic deprotonation events occurring at the WOC.

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Section: Resultsmentioning

confidence: 79%

Section: Discussionmentioning

confidence: 99%

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confidence: 99%

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Modulation of Flash-Induced Photosystem II Fluorescence by Events Occurring at the Water Oxidizing Complex

1999

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“…As a consequence, a dampened period 4 oscillation is observed when the F o is plotted as a function of flash number. Several authors have speculated about the cause of this S state-dependent quenching effect ( − ). This phenomenon provides another probe of the S state cycle, and we have used it to determine the S state generated by NO reduction.…”

Section: Resultsmentioning

confidence: 99%

Reduction of the Mn Cluster of the Water-Oxidizing Enzyme by Nitric Oxide: Formation of an S_-₂ State

et al. 2002

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The manganese cluster of the oxygen-evolving enzyme of photosystem II is chemically reduced upon interaction with nitric oxide at -30 degrees C. The state formed gives rise to an S = 1/2 multiline EPR signal [Goussias, Ch., Ioannidis, N., and Petrouleas, V. (1997) Biochemistry 36, 9261] that is attributed to a Mn(II)- Mn(III) dimer [Sarrou, J., Ioannidis, N., Deligiannakis, Y., and Petrouleas, V. (1998) Biochemistry 37, 3581]. In this work, we sought to establish whether the state could be assigned to a specific, reduced S state by using flash oxymetry, chlorophyll a fluorescence, and electron paramagnetic resonance spectroscopy. With the Joliot-type O(2) electrode, the first maximum of oxygen evolution was observed on the sixth or seventh flash. Three saturating pre-flashes were required to convert the flash pattern characteristic of NO-reduced samples to that of the untreated control (i.e., O(2) evolution maximum on the third flash). Measurements of the S state-dependent level of chlorophyll fluorescence in NO-treated PSII showed a three-flash downshift compared to untreated controls. In the EPR study, the maximum S(2) multi-line EPR signal was observed after the fourth flash. The results from all three methods are consistent with the Mn cluster being in a redox state corresponding to an S(-2) state in a majority of centers after treatment with NO. We were unable to generate the Mn(II)-Mn(III) multi-line signal using hydrazine as a reductant; it appears that the valence distribution and possibly the structure of the Mn cluster in the S(-2) state are dependent on the nature of the reductant that is used.

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“…In addition, the coupling between P680 + and the WOC has been shown to be mediated by the redox-active tyrosine Y Z . 43,44 The mishits in the S i -state transitions originate from the transiently blocked RCs ("closed RCs") during the actinic flash because of the existence of a population of P680 + and/or Q A − via dynamic equilibria at the donor and acceptor side, respectively, 45,46 as well as from competing dissipative recombination reactions. 47 The average value of α attains a minimum of about 0.06, and it strongly depends on the pH 48,49 and on the replacement of exchangeable protons with deuterons, thus illustrating the effects of hydrogen-bonding networks.…”

Section: Reaction Mechanism Of Water Oxidation In Psiimentioning

confidence: 99%

Manganese Compounds as Water-Oxidizing Catalysts: From the Natural Water-Oxidizing Complex to Nanosized Manganese Oxide Structures

Najafpour¹,

et al. 2016

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All cyanobacteria, algae, and plants use a similar water-oxidizing catalyst for water oxidation. This catalyst is housed in Photosystem II, a membrane-protein complex that functions as a light-driven water oxidase in oxygenic photosynthesis. Water oxidation is also an important reaction in artificial photosynthesis because it has the potential to provide cheap electrons from water for hydrogen production or for the reduction of carbon dioxide on an industrial scale. The water-oxidizing complex of Photosystem II is a Mn-Ca cluster that oxidizes water with a low overpotential and high turnover frequency number of up to 25-90 molecules of O2 released per second. In this Review, we discuss the atomic structure of the Mn-Ca cluster of the Photosystem II water-oxidizing complex from the viewpoint that the underlying mechanism can be informative when designing artificial water-oxidizing catalysts. This is followed by consideration of functional Mn-based model complexes for water oxidation and the issue of Mn complexes decomposing to Mn oxide. We then provide a detailed assessment of the chemistry of Mn oxides by considering how their bulk and nanoscale properties contribute to their effectiveness as water-oxidizing catalysts.

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Cited by 24 publications

References 36 publications

Modulation of Flash-Induced Photosystem II Fluorescence by Events Occurring at the Water Oxidizing Complex

Modulation of Flash-Induced Photosystem II Fluorescence by Events Occurring at the Water Oxidizing Complex

Reduction of the Mn Cluster of the Water-Oxidizing Enzyme by Nitric Oxide: Formation of an S_-₂ State

Manganese Compounds as Water-Oxidizing Catalysts: From the Natural Water-Oxidizing Complex to Nanosized Manganese Oxide Structures

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Untitled

Cited by 24 publications

References 36 publications

Modulation of Flash-Induced Photosystem II Fluorescence by Events Occurring at the Water Oxidizing Complex

Modulation of Flash-Induced Photosystem II Fluorescence by Events Occurring at the Water Oxidizing Complex

Reduction of the Mn Cluster of the Water-Oxidizing Enzyme by Nitric Oxide: Formation of an S-2 State

Manganese Compounds as Water-Oxidizing Catalysts: From the Natural Water-Oxidizing Complex to Nanosized Manganese Oxide Structures

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Reduction of the Mn Cluster of the Water-Oxidizing Enzyme by Nitric Oxide: Formation of an S_-₂ State