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- Title
Theoretical study of the EPR spectrum of the STyrZ metalloradical intermediate state of the O-evolving complex of photosystem II.
- Authors
Zahariou, Georgia; Ioannidis, Nikolaos
- Abstract
The intermediates trapped during the transitions between the consecutive S-states of the oxygen-evolving complex (OEC) of photosystem II (PSII) contain the free radical TyrZ interacting magnetically with the Mn-cluster (MnCa). In this paper, we present a theoretical study of the EPR spectrum of the STyrZ metalloradical intermediate state, which has been recently detected in MeOH-containing PSII preparations. For this analysis, we use two different approximations: the first, simpler one, is the point-dipole approach, where the two interacting spins are the S = 1/2 of TyrZ and the ground spin state of S = 3 of the OEC being in the S state. The second approximation is based on previous proposals indicating that the ground spin state ( S = 3) of the S state arises from an antiferromagnetic exchange coupling between the S = 9/2 of the Mn(IV)CaO and the S = 3/2 of the external Mn(IV) of the OEC. Under the above assumption, the second approximation involves three interacting spins, denoted S (Mn(IV)Ca) = 9/2, S (Mn(IV)) = 3/2 and S (TyrZ) = 1/2. Accordingly, the tyrosine radical is exposed to dipolar interactions with both fragments of the OEC, while an antiferromagnetic exchange coupling within the '3 + 1' structural motif of the OEC is also considered. By application of the first-point-dipole approach, the inter-spin distance that simulates the experimental spectrum is not consistent with the theoretical models that were recently reported for the OEC in the S state. Instead, the recent models are consistent with the results of the analysis that is performed by using the second, more detailed, approach.
- Subjects
PHOTOSYSTEMS; OXYGEN-evolving complex (Photosynthesis); ELECTRON paramagnetic resonance spectroscopy; TYROSINE; ANTIFERROMAGNETISM; OXIDATION states; EXCHANGE interactions (Magnetism)
- Publication
Photosynthesis Research, 2016, Vol 130, Issue 1-3, p417
- ISSN
0166-8595
- Publication type
Article
- DOI
10.1007/s11120-016-0274-6