A model for the simulation of the EPR spectra of chromophores in partially oriented membrane multilayers

Blum, Haywood; Salerno, John C.; Leigh, John S.

doi:10.1016/0022-2364(78)90108-7

Cited by 22 publications

(35 citation statements)

References 13 publications

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“…For simulations involving oriented samples, the orientational averaging technique described by Blum, et al [24] for partially ordered membrane multilayers is used to weight w is the angle between the membrane normals and the field direction and is known from the experiment, whereas a must be averaged over 360° because there is no prefer~ntial ordering of the thylakoid membranes transverse to the membrane normal.…”

Section: T I N G T H E P O 1 a R I Za T I On We I G H T I N G F O R mentioning

confidence: 99%

Orientation dependence of radical pair interactions in spinach chloroplasts

McCracken

Sauer

1983

Biochimica et Biophysica Acta (BBA) - Bioenergetics

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Section: T I N G T H E P O 1 a R I Za T I On We I G H T I N G F O R mentioning

confidence: 99%

Orientation dependence of radical pair interactions in spinach chloroplasts

McCracken

Sauer

1983

Biochimica et Biophysica Acta (BBA) - Bioenergetics

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“…Rutherford found that for cyt b559+ in an oriented PS II sample, the gz peak was at a maximum with the magnetic field H parallel to the membrane plane (a = Oo) and the gy peak w& at a maximum with H perpendicular to the membrane plane (0 = 90") Blum et al (1978b), it is possible to generate EPR spectra and examine differences in the spectra due to variation in the angle of the sample with respect to the magnetic field (a) and in the degree of disorder (a). By comparison of these curves with EPR spectra generated at various o values, the mosaic spread Q can be determined.…”

Section: Cytochrome B559+ Epr Signalmentioning

confidence: 99%

“…Using an algorithm by Blum et al (1978b), a FORTRAN program was written to produce a series of-simulations by systematically varying both the angle o with respect to the magnetic field H and the mosaic spread Q. The simulation program was first checked by reproducing the results of Blum et al for cytochrome c-oxidase (Blum et al 1978a).…”

Section: Simulation Of Cyt B559+ Epr Spectramentioning

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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“…The disorder or mosaic spread 123,124 can be due to several factors: imperfect stacking of the membranes on the substrate film, disorder of PS II proteins within the membranes, or disorder of the OEC within the PS II proteins. There is no way to assign the contribution of each factor to the total mosaic spread.…”

Section: Mosaic Spread Determination By Eprmentioning

confidence: 99%

“…The dichroic ratio (here, amplitude at 90° divided by that at 0°) was taken at the ~ 3260 G. This dichroic ratio ("Signal II ratio") was related to the dichroism in the cytochrome b 559 EPR signal 21,22,112,124,125,128 to obtain the mosaic spread, or half-width of the Gaussian distribution of a particular vector in PS II samples. 126 In previous work from this laboratory, 126 a calibration line has been constructed, which equates mosaic spread to a measured Signal II ratio.…”

Section: Mosaic Spread Determination By Eprmentioning

confidence: 99%

X-ray absorption spectroscopy on the calcium cofactor to the manganese cluster in photosynthetic oxygen evolution

Cinco¹

1999

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PS II). To further test and verify whetherCa is close to the Mn cluster, we substituted strontium for Ca and probed from the Sr point of view for any nearby Mn. The extended X-ray absorption fine structure (EXAFS) of Sr-reactivated PS II indicates major differences between the intact and NH 2 OH-treated samples. In intact samples, the Fourier transform of the Sr EXAFS shows a Fourier peak that is missing in inactive samples. This peak II is best simulated by two Mn neighbors at a distance of 3.5 Å, confirming the proximity of Ca (Sr) cofactor to the Mn cluster. In addition, polarized Sr EXAFS on oriented Sr-reactivated samples shows this peak II is dichroic: large magnitude at 10° (angle between the PS II membrane normal and the x-ray electric field vector) and small at 80°. Analysis of the dichroism yields the relative angle between the Sr-Mn vector and membrane normal (23° ± 4°), and the isotropic coordination number for these layered samples.ii X-ray absorption spectroscopy has also been employed to assess the degree of similarity between the manganese cluster in PS II and a family of synthetic manganese complexes containing the distorted cubane [Mn 4 O 3 X] core (X = benzoate, acetate, methoxide, hydroxide, azide, fluoride, chloride or bromide). In addition, Mn 4 O 3 Cl complexes containing three or six terminal Cl ligands at three of the Mn were included in this study. The EXAFS method detects the small changes in the core structures as X is varied in this series, and serves to exclude these distorted cubanes of C 3v symmetry as a topological model for the Mn catalytic cluster.The sulfur K-edge x-ray absorption near-edge structure (XANES) spectra for the amino acids cysteine, methionine, their corresponding oxidized forms cystine and methionine sulfoxide, and glutathione show distinct differences between the thiol and disulfide forms. Sulfur XANES is also used to detect changes (within 5%) of the thiol-to-disulfide ratio in whole human blood, plasma, and erythrocytes.iii To my parents, and to my brothers Raoul and Dannyi v

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A model for the simulation of the EPR spectra of chromophores in partially oriented membrane multilayers

Cited by 22 publications

References 13 publications

Orientation dependence of radical pair interactions in spinach chloroplasts

Orientation dependence of radical pair interactions in spinach chloroplasts

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

X-ray absorption spectroscopy on the calcium cofactor to the manganese cluster in photosynthetic oxygen evolution

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