title: Oxidation states of the manganese cluster during the flash-induced S-state cycle of the photosynthetic oxygen-evolving complex.
abstract: The Mn K-edge x-ray absorption spectra for the pure S states of the tetranuclear Mn cluster of the oxygen-evolving complex of photosystem II during flash-induced S-state cycling have been determined. The relative S-state populations in samples given 0, 1, 2, 3, 4, or 5 flashes were determined from fitting the flash-induced electron paramagnetic resonance (EPR) multiline signal oscillation pattern to the Kok model. The edge spectra of samples given 0, 1, 2, or 3 flashes were combined with EPR information to calculate the pure S-state edge spectra. The edge positions (defined as the zero-crossing of the second derivatives) are 6550.1, 6551.7, 6553.5, and 6553.8 eV for S0, S1, S2, and S3, respectively. In addition to the shift in edge position, the S0--> S1 and S1--> S2 transitions are accompanied by characteristic changes in the shape of the edge, both indicative of Mn oxidation. The edge position shifts very little (0.3 eV) for the S2--> S3 transition, and the edge shape shows only subtle changes. We conclude that probably no direct Mn oxidation is involved in this transition. The proposed Mn oxidation state assignments are as follows: S0 (II, III, IV, IV) or (III, III, III, IV), S1 (III, III, IV, IV), S2 (III, IV, IV, IV), S3 (III, IV, IV, IV).
authors.affiliation: Structural Biology Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors.forename: T A
authors.initials: TA
authors.lastname: Roelofs
authors.forename: W
authors.initials: W
authors.lastname: Liang
authors.forename: M J
authors.initials: MJ
authors.lastname: Latimer
authors.forename: R M
authors.initials: RM
authors.lastname: Cinco
authors.forename: A
authors.initials: A
authors.lastname: Rompel
authors.forename: J C
authors.initials: JC
authors.lastname: Andrews
authors.forename: K
authors.initials: K
authors.lastname: Sauer
authors.forename: V K
authors.initials: VK
authors.lastname: Yachandra
authors.forename: M P
authors.initials: MP
authors.lastname: Klein