van der Est, A. and Hager-Braun, C. and Leibl, W. and Hauska, Günter and Stehlik, D. (1998) Transient electron paramagnetic resonance spectroscopy on green-sulfur bacteria and heliobacteria at two microwave frequencies. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS, 1409 (2). pp. 87-98. ISSN 0005-2728, 0006-3002
Full text not available from this repository. (Request a copy)Abstract
Spin polarized transient EPR spectra taken at X-band (9 GHz) and K-band (24 GHz) of membrane fragments of Chlorobium tepidum and Heliobacillus mobilis are presented along with the spectra of two fractions obtained in the purification of reaction centers (RC) from C. tepidum. The lifetime of P+. is determined by measuring the decay of the EPR signals following relaxation of the initial spin polarization. All samples except one of the RC fractions show evidence of light induced charge separation and formation of chlorophyll triplet states. The lifetime of P+. is found to be biexponential with components of 1.5 ms and 30 ms for C. tepidum and 1.0 and 4.5 ms for He. mobilis at 100 K. In both cases, the rates are assigned to recombination from F-x(-). The spin polarized radical pair spectra for both species are similar and those from He. mobilis at room temperature and 100 K are identical. In all cases, an emission/absorption polarization pattern with a net absorption is observed. A slight narrowing of the spectra and a larger absorptive net polarization is found at K-band. No out-of-phase echo modulation is observed. Taken together, the recombination kinetics, the frequency dependence of the spin polarization and the absence of an out-of-phase echo signal lead to the assignment of the spectra to the contribution from P+. to the state P+.Fx-. The origin of the net polarization and its frequency dependence are discussed in terms of singlet-triplet mixing in the precursor. It is shown that the field-dependent polarization expected to develop during the 600-700 ps lifetime of P(+.)A(0)(-.) is in qualitative agreement with the observed spectra. The identity that the acceptor preceding F-x and the conflicting evidence from EPR, optical methods and chemical analyses of the samples are discussed. (C) 1998 Elsevier Science B.V. All rights reserved.
| Item Type: | Article |
|---|---|
| Uncontrolled Keywords: | PHOTOSYNTHETIC REACTION-CENTER; CORRELATED RADICAL PAIRS; PHOTOSYSTEM-I; HELIOBACILLUS-MOBILIS; SPIN POLARIZATION; CHLOROBIUM-LIMICOLA; FTIR SPECTROSCOPY; CHARGE SEPARATION; TRANSFER KINETICS; EXCITED-STATES; photosynthesis; electron transfer; quinone; spin polarization; sequential radical pair |
| Subjects: | 500 Science > 580 Botanical sciences |
| Divisions: | Biology, Preclinical Medicine > Institut für Pflanzenwissenschaften > Alumni or Retired > Prof. Dr. Günter Hauska |
| Depositing User: | Dr. Gernot Deinzer |
| Date Deposited: | 09 Feb 2023 07:33 |
| Last Modified: | 09 Feb 2023 07:33 |
| URI: | https://pred.uni-regensburg.de/id/eprint/49275 |
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