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The Semiquinone-Iron Complex of Photosystem II: Structural Insights from ESR and Theoretical Simulation; Evidence that the Native Ligand to the Non-Heme Iron Is Carbonate

Cox, Nicholas; Jin, Lu; Jaszewski, Adrian; Smith, Paul J.; Krausz, Elmars; Rutherford, A. William; Pace, Ronald

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The semiquinone-iron complex of photosystem II was studied using electron spin resonance (ESR) spectroscopy and density functional theory calculations. Two forms of the signal were investigated: 1), the native g approximately 1.9 form; and 2), the g approximately 1.84 form, which is well known in purple bacterial reaction centers and occurs in photosystem II when treated with formate. The g approximately 1.9 form shows low- and high-field edges at g approximately 3.5 and g < 0.8, respectively,...[Show more]

dc.contributor.authorCox, Nicholas
dc.contributor.authorJin, Lu
dc.contributor.authorJaszewski, Adrian
dc.contributor.authorSmith, Paul J.
dc.contributor.authorKrausz, Elmars
dc.contributor.authorRutherford, A. William
dc.contributor.authorPace, Ronald
dc.date.accessioned2016-03-24T00:03:19Z
dc.date.available2016-03-24T00:03:19Z
dc.identifier.issn0006-3495
dc.identifier.urihttp://hdl.handle.net/1885/100874
dc.description.abstractThe semiquinone-iron complex of photosystem II was studied using electron spin resonance (ESR) spectroscopy and density functional theory calculations. Two forms of the signal were investigated: 1), the native g approximately 1.9 form; and 2), the g approximately 1.84 form, which is well known in purple bacterial reaction centers and occurs in photosystem II when treated with formate. The g approximately 1.9 form shows low- and high-field edges at g approximately 3.5 and g < 0.8, respectively, and resembles the g approximately 1.84 form in terms of shape and width. Both types of ESR signal were simulated using the theoretical approach used previously for the BRC complex, a spin Hamiltonian formalism in which the semiquinone radical magnetically interacts (J approximately 1 cm(-1)) with the nearby high-spin Fe(2+). The two forms of ESR signal differ mainly by an axis rotation of the exchange coupling tensor (J) relative to the zero-field tensor (D) and a small increase in the zero-field parameter D ( approximately 6 cm(-1)). Density functional theory calculations were conducted on model semiquinone-iron systems to identify the physical nature of these changes. The replacement of formate (or glutamate in the bacterial reaction centers) by bicarbonate did not result in changes in the coupling environment. However, when carbonate (CO(3)(2-)) was used instead of bicarbonate, the exchange and zero-field tensors did show changes that matched those obtained from the spectral simulations. This indicates that 1), the doubly charged carbonate ion is responsible for the g approximately 1.9 form of the semiquinone-iron signal; and 2), carbonate, rather than bicarbonate, is the ligand to the iron.
dc.description.sponsorshipThe authors acknowledge the support of the Australian Research Council. A.R.J. thanks the University of Wroclaw for a two-year sabbatical for allowing a postdoctoral fellowship at Australian National University. The computations were performed using the Wroclaw Center of Networking and Supercomputing (grant No. 48) facility. A.W.R. was supported by the Research School of Chemistry as the Craig Professor, as a visiting research fellow, and by the France Australia Science and Technology Program (FAST).
dc.publisherBiophysical Society
dc.rights© 2009 by the Biophysical Society
dc.sourceBiophysical Journal
dc.subjectabsorption
dc.subjectbenzoquinones
dc.subjectcarbonates
dc.subjectcomputer simulation
dc.subjectelectron spin resonance spectroscopy
dc.subjectiron
dc.subjectligands
dc.subjectphotosystem ii protein complex
dc.subjectquantum theory
dc.subjectspinacia oleracea
dc.subjecttemperature
dc.titleThe Semiquinone-Iron Complex of Photosystem II: Structural Insights from ESR and Theoretical Simulation; Evidence that the Native Ligand to the Non-Heme Iron Is Carbonate
dc.typeJournal article
local.description.notesImported from ARIES
local.identifier.citationvolume97
dc.date.issued2009
local.identifier.absfor030606
local.identifier.absfor030699
local.identifier.ariespublicationu4217927xPUB417
local.publisher.urlhttp://www.biophysics.org/
local.type.statusPublished Version
local.contributor.affiliationCox, Nicholas, College of Physical and Mathematical Sciences, CPMS Research School of Chemistry, RSC General, The Australian National University
local.contributor.affiliationJin, Lu, College of Physical and Mathematical Sciences, CPMS Research School of Chemistry, RSC General, The Australian National University
local.contributor.affiliationJaszewski, Adrian, College of Physical and Mathematical Sciences, CPMS Research School of Chemistry, RSC General, The Australian National University
local.contributor.affiliationSmith, Paul, College of Physical and Mathematical Sciences, CPMS Research School of Chemistry, RSC General, The Australian National University
local.contributor.affiliationKrausz, Elmars, College of Physical and Mathematical Sciences, CPMS Research School of Chemistry, RSC General, The Australian National University
local.contributor.affiliationRutherford, Alfred W, CEA-Saclay, France
local.contributor.affiliationPace, Ronald, College of Physical and Mathematical Sciences, CPMS Research School of Chemistry, RSC General, The Australian National University
local.identifier.essn1542-0086
local.bibliographicCitation.issue7
local.bibliographicCitation.startpage2024
local.bibliographicCitation.lastpage2033
local.identifier.doi10.1016/j.bpj.2009.06.033
dc.date.updated2016-06-14T08:59:43Z
local.identifier.scopusID2-s2.0-70349928560
local.identifier.thomsonID000270586000025
CollectionsANU Research Publications

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