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Title: Structural studies of iron and manganese in photosynthetic reaction centers

Abstract

Electron paramagnetic resonance (EPR) and x-ray absorption spectroscopy (XAS) were used to characterize components involved in the light reactions of photosynthetic reaction centers from spinach and a thermophilic cyanobacterium, Synechococcus sp.: center X, the low electron potential acceptor in Photosystem I (PS I) and the Mn complex involved in water oxidation and oxygen evolution. The dependence of its EPR amplitude on microwave power and temperature indicate an Orbach spin relaxation mechanism involving an excited state at 40 cm/sup -1/. This low energy contributes to its unusually anisotropic g-tensor. XAS of iron in PS I preparations containing ferredoxins A, B and X are consistent with a model with (4Fe-4S) ferredoxins, which are presumably centers A and B and (2Fe-2S) ferredoxins, which would be X. Illumination of dark-adapted Synechococcus PS II samples at 220 to 240 K results in the formation of the multiline EPR signal previously assigned as a Mn S/sub 2/ species, and g = 1.8 and 1.9 signals of Fe/sup 2 +/ Q/sub A//sup -/. In contrast to spinach, illumination at 110 to 160 K produces only a new EPR signal at g = 1.6 which we assign to another configuration of Fe/sup 2+ - Q/sup -/. Following illuminationmore » of a S/sub 1/ sample at 140 K or 215 K, the Mn x-ray absorption edge inflection energy changes from 6550 eV to 6551 eV, indicating an oxidation of Mn, and average valences greater than Mn(II). Concomitant changes in the shape of the pre-edge spectrum indicate oxidation of Mn(III) to Mn(IV). The Mn EXAFS spectrum of PS II from Synechococcus is similar in the S/sub 1/ and S/sub 2/ states, indicating O or N ligands at 1.75 +- 0.05 A, transition metal neighbor(s) at 2.75 +- 0.05 A, and N and O ligands at 2.2 A with heterogeneous bond lengths; these data demonstrate the presence of a di-..mu..-oxo bridged Mn structure. 202 refs., 40 figs., 7 tabs.« less

Authors:
Publication Date:
Research Org.:
Lawrence Berkeley Lab., CA (USA)
OSTI Identifier:
5692498
Report Number(s):
LBL-24474
ON: DE88005737
DOE Contract Number:  
AC03-76SF00098
Resource Type:
Technical Report
Resource Relation:
Other Information: Portions of this document are illegible in microfiche products
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; 59 BASIC BIOLOGICAL SCIENCES; FERREDOXIN; ELECTRON SPIN RESONANCE; X-RAY SPECTROSCOPY; PHOTOSYNTHETIC REACTION CENTERS; ELECTROPHORESIS; PHOTOSYNTHETIC BACTERIA; PHYCOBILIPROTEINS; SPINACH; FOOD; MAGNETIC RESONANCE; METALLOPROTEINS; ORGANIC COMPOUNDS; PLANTS; PROTEINS; RESONANCE; SPECTROSCOPY; VEGETABLES; 140505* - Solar Energy Conversion- Photochemical, Photobiological, & Thermochemical Conversion- (1980-); 550200 - Biochemistry

Citation Formats

McDermott, A E. Structural studies of iron and manganese in photosynthetic reaction centers. United States: N. p., 1987. Web.
McDermott, A E. Structural studies of iron and manganese in photosynthetic reaction centers. United States.
McDermott, A E. 1987. "Structural studies of iron and manganese in photosynthetic reaction centers". United States.
@article{osti_5692498,
title = {Structural studies of iron and manganese in photosynthetic reaction centers},
author = {McDermott, A E},
abstractNote = {Electron paramagnetic resonance (EPR) and x-ray absorption spectroscopy (XAS) were used to characterize components involved in the light reactions of photosynthetic reaction centers from spinach and a thermophilic cyanobacterium, Synechococcus sp.: center X, the low electron potential acceptor in Photosystem I (PS I) and the Mn complex involved in water oxidation and oxygen evolution. The dependence of its EPR amplitude on microwave power and temperature indicate an Orbach spin relaxation mechanism involving an excited state at 40 cm/sup -1/. This low energy contributes to its unusually anisotropic g-tensor. XAS of iron in PS I preparations containing ferredoxins A, B and X are consistent with a model with (4Fe-4S) ferredoxins, which are presumably centers A and B and (2Fe-2S) ferredoxins, which would be X. Illumination of dark-adapted Synechococcus PS II samples at 220 to 240 K results in the formation of the multiline EPR signal previously assigned as a Mn S/sub 2/ species, and g = 1.8 and 1.9 signals of Fe/sup 2 +/ Q/sub A//sup -/. In contrast to spinach, illumination at 110 to 160 K produces only a new EPR signal at g = 1.6 which we assign to another configuration of Fe/sup 2+ - Q/sup -/. Following illumination of a S/sub 1/ sample at 140 K or 215 K, the Mn x-ray absorption edge inflection energy changes from 6550 eV to 6551 eV, indicating an oxidation of Mn, and average valences greater than Mn(II). Concomitant changes in the shape of the pre-edge spectrum indicate oxidation of Mn(III) to Mn(IV). The Mn EXAFS spectrum of PS II from Synechococcus is similar in the S/sub 1/ and S/sub 2/ states, indicating O or N ligands at 1.75 +- 0.05 A, transition metal neighbor(s) at 2.75 +- 0.05 A, and N and O ligands at 2.2 A with heterogeneous bond lengths; these data demonstrate the presence of a di-..mu..-oxo bridged Mn structure. 202 refs., 40 figs., 7 tabs.},
doi = {},
url = {https://www.osti.gov/biblio/5692498}, journal = {},
number = ,
volume = ,
place = {United States},
year = {Sun Nov 01 00:00:00 EST 1987},
month = {Sun Nov 01 00:00:00 EST 1987}
}

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