Properties of iodide-activated photosynthetic water-oxidizing complexes

Rashid, Abdur; Homann, Peter H.

doi:10.1016/0005-2728(92)90086-h

Cited by 29 publications

(23 citation statements)

References 31 publications

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“…Indeed, several studies suggest that Cl À is not a direct ligand to the OEC metal-cluster. 38,39,52 For example, in the recent extended X-ray absorption fine structure (EXAFS) work on PSII (isolated from spinach) which had been biochemically infiltrated with bromide, Haumann et al 39 concluded that a bromide ion is bound at z5 A ˚from Mn or Ca. This distance differs from those reported here, but this difference is probably within the limitation imposed by the resolution of the X-ray diffraction.…”

Section: Resultsmentioning

confidence: 99%

X-ray crystallography identifies two chloride binding sites in the oxygen evolving centre of Photosystem II

Murray

Maghlaoui

Kargul

et al. 2008

Energy Environ. Sci.

126

114

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Section: Resultsmentioning

confidence: 99%

X-ray crystallography identifies two chloride binding sites in the oxygen evolving centre of Photosystem II

Murray

Maghlaoui

Kargul

et al. 2008

Energy Environ. Sci.

126

114

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“…Addition of anions (as their sodium salt) to pH 10/Cl --depleted PS-II was done at pH 7.3, i.e. under conditions in which irreversible inhibition of oxygen evolution is minimized and yet PS-II is still sensitive to treatments that affect Cl --dependent oxygen-evolving activity (Rashid & Homann, 1992;Homann, 1993). Following 10-20 min of incubation, the pH was lowered to pH 6.3 as described above.…”

Section: Methodsmentioning

confidence: 99%

Properties of the Chloride-Depleted Oxygen-Evolving Complex of Photosystem II Studied by Electron Paramagnetic Resonance

Vliet

Rutherford

1996

Biochemistry

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The effects of different Cl- depletion treatments in photosystem II (PS-II)-enriched membranes have been investigated by electron paramagnetic resonance (EPR) spectroscopy and by measurements of oxygen-evolving activity. The results indicated that the oxygen-evolving complex of PS-II exhibits two distinct Cl(-)-dependent properties. (1) After Cl(-)-free washes at pH 6.3, a reversibly altered distribution of structural states of PS-II was observed, manifested as the appearance of a g = 4 EPR signal from the S2 state in a significant fraction of centers (20-40%) at the expense of the S2 multiline signal. In addition, small but significant changes in the shape of the S2 multiline EPR signal were observed. Reconstitution of Cl- to Cl(-)-free washed PS-II rapidly reversed the observed effects of the Cl(-)-free washing. The anions, SO4(2-) and F-, which are often used during Cl- depletion treatments, had no effect on the S2 EPR properties of PS-II under these conditions in the absence or presence of Cl-. Flash experiments and measurements of oxygen evolution versus light intensity indicated that the two structural states observed after the removal of Cl- at pH 6.3 originated from oxygen-evolving centers exhibiting a lowered quantum yield of water oxidation. (2) Depletion of Cl- in PS-II by pH 10 treatment reversibly inhibited the oxygen-evolving activity to approximately 15%. The pH 10 treatment depleted the Cl- from a site which is considered to be equivalent to that studied in most earlier work on Cl(-)-depleted PS-II. The S2 state in pH 10/Cl(-)-depleted PS-II was reversibly modified to a state from which no S2 multiline EPR signal was generated and which exhibited an intense S2 g = 4 EPR signal corresponding to at least 40% of the centers but possibly to a much larger fraction of centers. The state responsible for the intense S2 g = 4 signal generated under these conditions is unlike that observed after removal of Cl- from PS-II at pH 6.3, in that this state was more stable in the dark, showing a half-decay time of approximately 1.5 h at 0 degrees C, and was unable to undergo further charge accumulation. Nevertheless, a fraction of centers, probably different from those exhibiting the S2 g = 4 signal, was able to advance to the formal S3 state, giving rise to a narrow EPR signal around g = 2. Addition of the anions SO4(2-) or F- to pH 10/Cl(-)-depleted PS-II affected the properties of PS-II, resulting in EPR properties of the S2 state similar to those reported earlier following Cl- depletion treatment of PS-II in the presence of these anions. Surprisingly, after addition of F-, the g = 4 EPR signal showed a damped flash-dependent oscillation. In addition, a narrow signal around g = 2, corresponding to the formal S3 state, also showed a damped flash-dependent oscillation pattern. The presence of oscillating EPR signals (albeit damped) in F(-)-treated pH 10/Cl(-)-depleted PS-II indicates functional enzyme turnover. This was confirmed by measurements of the oxygen-evolving activity versus light intensity which indicat...

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“…Replacement of C1-with Br-restores normal oxygen evolution activity . (On0 et al, 1987;Haddy & VSinngkd, 1990;Kelly & Izawa, 1978;, and replacement with I-results in -50% of normal activity (Rashid & Homann, 1992). .…”

Section: Discussionmentioning

confidence: 99%

X-ray absorption spectroscopy and EPR studies of oriented spinach thylakoid preparations

Andrews

1995

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In this study, oriented Photosystem 11 (PS n) particles from spinach chloroplasts are studied with electron paramagnetic resonance (EPR) and x-ray absorption spectroscopy VAS) to determine more details of the structure of the oxygen evolving complex (OEC).The nature of halide binding to Mn is also studied with C1 K-edge and Mn EXAFS (extended x-ray absorption fine structure) of Mn-C1 model compounds, and with Mn EXAFS of oriented PS 1T in which Br has replaced C1.In chapter 2, oriented PS 11 particles from spinach were studied with EPR spectroscopy. The mosaic spread for these samples was determined by comparison of the oxidized cytochrome b559 (cyt b559+) signal measured at angles of 0" to 360" between the EPR magnetic field and sample membrane normal with simulations of oriented cyt b559+.The tyrosine YD+ signal was measured for these oriented samples at 0" and 90°, and a linear relationship was found between the dichroism found in the tyrosine YD+ signal and the mosaic spread.In chapters 3 and 4, Mn XAS was performed on oriented PS 11 membrane particles isolated from spinach. These studies were on control samples (chapter 3) and on samples treated with ammonia (chapter 4), a water analog which can yield insight into the binding of water by the OEC. Structural features of the tetranuclear Mn cluster and the orientation of the cluster with respect to the lipid bilayer were determined in the S2 state of the Kok cycle 1 for control samples, and on the annealed S2 state for the ammonia-treated samples.Variation of the sample orientation with respect to the x-ray e-vector yields highly dichroic In chapter 5, the binding of halide to Mn was studied using C1 K-edge XAS and Mn EXAFS on Mn-CI model compounds, and Mn EXAFS on oriented Br-treated PS IL From the C1 K-edges of model compounds, direct ligation of C1 to Mn could be confirmed with the presence of a pre-edge feature: 'a forbidden 1s to 3d transition which is seen due to mixing of Mn 3d orbitals with C13p orbitals. Bridging and terminal C1 bonds to Mn could be distinguish& EXAFS of Mn-C1 model compounds revealed that Mn-C1 interactions, especially bridging interactions, make an important contribution to the EXAFS. EXAFS of oriented Br-treated PS 11 showed differences from EXAFS of control CI-treated PS II that were on the same order as the variation from sample to sample. Fits to Br-treated and Cl control samples were also inconclusive. Thus, it is not possible to 9 establish or rule out direct ligation of C1 to Mn in the OEC with these studies.2

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Properties of iodide-activated photosynthetic water-oxidizing complexes

Cited by 29 publications

References 31 publications

X-ray crystallography identifies two chloride binding sites in the oxygen evolving centre of Photosystem II

X-ray crystallography identifies two chloride binding sites in the oxygen evolving centre of Photosystem II

Properties of the Chloride-Depleted Oxygen-Evolving Complex of Photosystem II Studied by Electron Paramagnetic Resonance

X-ray absorption spectroscopy and EPR studies of oriented spinach thylakoid preparations

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