Q-band EPR of the S2 state of photosystem II confirms an S = 5/2 origin of the X-band g = 4.1 signal.

Alice Haddy, K. V. Lakshmi, Gary W Brudvig, Harry A. Frank

Research output: Contribution to journalArticle

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Abstract

Disagreement has remained about the spin state origin of the g = 4.1 EPR signal observed at X-band (9 GHz) from the S2 oxidation state of the Mn cluster of Photosystem II. In this study, the S2 state of PSII-enriched membrane fragments was examined at Q-band (34 GHz), with special interest in low-field signals. Light-induced signals at g = 3.1 and g = 4.6 were observed. The intensity of the signal at g = 3.1 was enhanced by the presence of F- and suppressed by the presence of 5% ethanol, indicating that it was from the same spin system as the X-band signal at g = 4.1. The Q-band signal at g = 4.6 was also enhanced by F-, but not suppressed by 5% ethanol, making its identity less clear. Although it can be accounted for by the same spin system, other sources for the signal are considered. The observation of the signal at g = 3.1 agrees well with a previous study at 15.5 GHz, in which the X-band g = 4.1 signal was proposed to arise from the middle Kramers doublet of a near rhombic S = 5/2 system. Zero-field splitting values of D = 0.455 cm(-1) and E/D = 0.25 are used to simulate the spectra.

Original languageEnglish
Pages (from-to)2885-2896
Number of pages12
JournalBiophysical Journal
Volume87
Issue number4
Publication statusPublished - Oct 2004

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Photosystem II Protein Complex
Ethanol
Observation
Light
Membranes

ASJC Scopus subject areas

  • Biophysics

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Q-band EPR of the S2 state of photosystem II confirms an S = 5/2 origin of the X-band g = 4.1 signal. / Haddy, Alice; Lakshmi, K. V.; Brudvig, Gary W; Frank, Harry A.

In: Biophysical Journal, Vol. 87, No. 4, 10.2004, p. 2885-2896.

Research output: Contribution to journalArticle

Haddy, Alice ; Lakshmi, K. V. ; Brudvig, Gary W ; Frank, Harry A. / Q-band EPR of the S2 state of photosystem II confirms an S = 5/2 origin of the X-band g = 4.1 signal. In: Biophysical Journal. 2004 ; Vol. 87, No. 4. pp. 2885-2896.
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