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MacMillan, Fraser 
ORCID: https://orcid.org/0000-0002-2410-4790, Lendzian, Friedhelm, Renger, Gernot and Lubitz, Wolfgang
(1995)
EPR and ENDOR investigation of the primary electron acceptor radical anion QA.bul.- in iron-depleted photosystem II membrane fragments.
Biochemistry, 34 (25).
pp. 8144-8156.
ISSN 0006-2960
Abstract
Photosystem II (PS II) membrane fragments were treated with trypsin at pH = 7.4 followed by incubation with o-phenanthroline and lithium perchlorate. This procedure removes and/or decouples the non-heme Fe2+ associated with the quinones QA and QB in the PS II reaction center (RC). Treatment of such samples (referred to as iron-depleted) with sodium dithionite or illumination in the presence of dichlorophenol indophenol (DCIP) and sodium ascorbate yielded EPR spectra similar to those of the plastoquinone-9 (PQ-9) radical anion generated in organic solvents. Q-band EPR yielded the principal values of the g-tensor for PQ-9.- in 2-propanol and QA.- in PS II. Electron nuclear double resonance (ENDOR) experiments were performed both on PQ-9.- in vitro and on QA.- in the iron-depleted PS II samples. For the former a complete set of isotropic 1H hyperfine coupling constants and hyperfine tensors of the two methyl groups and the alpha-proton were obtained. On the basis of H/D exchange experiments two different hydrogen bonds could be detected in frozen solution that are formed between the carbonyl oxygens of the radical and protons from the surrounding solvent molecules. The hydrogen bond distances were estimated using the point-dipole model. 1H-ENDOR spectra of QA.- in iron-depleted PS II samples have been measured in buffers made in H2O and D2O. The spectrum in deuterated buffer allowed the determination of two different methyl group hyperfine tensors. Differences detected between the spectra in protonated and deuterated buffer reveal the hyperfine tensors of two exchangeable protons belonging to hydrogen bonds between the oxygens of QA and specific protein residues. The assignment of these hydrogen bonds in PS II is discussed and compared with the situation found in the bacterial reaction center.
| Item Type: | Article |
|---|---|
| Faculty \ School: | Faculty of Science > School of Chemistry (former - to 2024) |
| UEA Research Groups: | Faculty of Science > Research Groups > Chemistry of Light and Energy Faculty of Science > Research Groups > Chemistry of Life Processes Faculty of Science > Research Centres > Centre for Molecular and Structural Biochemistry Faculty of Science > Research Groups > Biophysical Chemistry (former - to 2017) |
| Depositing User: | Pure Connector |
| Date Deposited: | 21 Jan 2015 11:58 |
| Last Modified: | 13 Nov 2024 00:39 |
| URI: | https://ueaeprints.uea.ac.uk/id/eprint/51869 |
| DOI: | 10.1021/bi00025a021 |
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