Absorption changes of Photosystem II donors and acceptors in algal cells

Lavergne, Jérôme

doi:10.1016/0014-5793(84)81006-6

Cited by 31 publications

(9 citation statements)

References 12 publications

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“…The largest extent at 443 nm, attributable to electrochromism, was observed with oxygen-evolving material (Figure 2, blue, solid line). Its difference spectrum was similar to previously reported ones (4,40,47,48,59,60). With Mn-depleted centers at pH 9 the spectral shape was similar to the former ones; however, the extent was about halved (Figure 2, blue, dotted line).…”

Section: Raw Absorption Difference Spectra and Their Deconvolutionsupporting

confidence: 88%

Tyrosine-Z in Oxygen-Evolving Photosystem II: A Hydrogen-Bonded Tyrosinate

1998

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In oxygen-evolving photosystem II (PSII), a tyrosine residue, D1Tyr161 (Y Z ), serves as the intermediate electron carrier between the catalytic Mn cluster and the photochemically active chlorophyll moiety P 680 . A more direct catalytic role of Y Z , as a hydrogen abstractor from bound water, has been postulated. That Y Z ox appears as a neutral (i.e. deprotonated) radical, Y Z • , in EPR studies is compatible with this notion. Data based on electrochromic absorption transients, however, are conflicting because they indicate that the phenolic proton remains on or near to Y Z ox . In Mn-depleted PSII the electron transfer between Y Z and P 680 + can be almost as fast as in oxygen-evolving material, however, only at alkaline pH. With an apparent pK of about 7 the fast reaction is suppressed and converted into an about 100-fold slower one which dominates at acid pH. In the present work we investigated the optical difference spectra attributable to the transition Y Z f Y Z ox as function of the pH. We scanned the UV and VIS range and used Mn-depleted PSII core particles and also oxygen-evolving ones. Comparing these spectra with published in vitro and in vivo spectra of phenolic compounds, we arrived at the following conclusions: In oxygen-evolving PSII Y Z resembles a hydrogen-bonded tyrosinate, Y Z (-) ‚‚‚H (+) ‚B. The phenolic proton is shifted toward a base B already in the reduced state and even more so in the oxidized state. The retention of the phenolic proton in a hydrogen-bonded network gives rise to a positive net charge in the immediate vicinity of the neutral radical Y Z • . It may be favorable both for the very rapid reduction by Y Z of P 680 + and for electron (not hydrogen) abstraction by Y Z • from the Mn-water cluster.Photosystem II (PSII) 1 produces molecular oxygen from water. It is located in photosynthetic membranes of plants and cyanobacteria. The inner core of PSII is a heterodimer of the D1D2 subunits which show homology with the L and M subunits of the purple bacterial RC (1). The primary electron donor of PSII, P 680 , is located close to the lumenal side of the membrane. The absorption of a quantum of light drives the charge separation between P 680 and the quinone acceptor at the stromal side (2). The very high redox potential of P 680 + drives water oxidation. It is a four-stepped process with at least four increasingly oxidized, metastable states S 0 to S 3 , plus a transient state S 4 that decays in milliseconds into S 0 under release of O 2 . P 680 + is reduced (in nanoseconds) by a redox-active tyrosine residue, Y Z (D1Tyr161 (3, 4)). Y Z ox is, in turn, reduced in microseconds by the oxygenevolving complex (OEC). The structure and exact location of the OEC is still ill-defined. It is formed by four manganese atoms (5, 6), possibly another redox cofactor, X (7-9), plus at least one Cl -ion (10) and one Ca 2+ (11, 12) ion. These cofactors serve various functions during water oxidation: The Mn cluster stores at least two of the oxidizing equivalents (namely on transitions S ...

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Section: Raw Absorption Difference Spectra and Their Deconvolutionsupporting

confidence: 88%

Tyrosine-Z in Oxygen-Evolving Photosystem II: A Hydrogen-Bonded Tyrosinate

1998

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“…This interpretation was confirmed by Saygin and Witt (1985) but challenged by Lavergne (1984Lavergne ( , 1986. The observed oscillation pattern of absorbance changes at 920 nm with flash number was compatible with assignment to the S2-state (Dismukes and Mathis, 1984).…”

Section: Plantssupporting

confidence: 69%

Magnetic Interactions Between Photosynthetic Reactants

Hoff

1986

Photochem & Photobiology

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“…Addition of p-benzoquinone, a protein cross-linker, blocks overall cell metabolism without stopping the primary photosynthetic reactions at the level of the thylakoid membrane. It results in a full oxidation of the plastoquinone pool in the dark (24,25), which we show here to considerably slow the reducing flux (slower than 0.1 s Ϫ1 , see Fig. 2A).…”

Section: Resultsmentioning

confidence: 56%

Interaction between Starch Breakdown, Acetate Assimilation, and Photosynthetic Cyclic Electron Flow in Chlamydomonas reinhardtii

Johnson

Alric

2012

Journal of Biological Chemistry

114

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Background: Most green microalgae grow photoautotrophically and heterotrophically. Results: The origin of chloroplast reductants in the dark is starch and/or acetate. Conclusion: It is possible to distinguish between these two carbon reserves and measure the reducing flux of carbohydrate catabolism using spectroscopic methods. Significance: The glycolytic flux in the chloroplast of green algae is faster than in plants.

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Absorption changes of Photosystem II donors and acceptors in algal cells

Cited by 31 publications

References 12 publications

Tyrosine-Z in Oxygen-Evolving Photosystem II: A Hydrogen-Bonded Tyrosinate

Tyrosine-Z in Oxygen-Evolving Photosystem II: A Hydrogen-Bonded Tyrosinate

Magnetic Interactions Between Photosynthetic Reactants

Interaction between Starch Breakdown, Acetate Assimilation, and Photosynthetic Cyclic Electron Flow in Chlamydomonas reinhardtii

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