Structural change of the Mn cluster during the S2 {yields} S3 state transition of the oxygen-evolving complex of Photosystem II. Does it reflect the onset of water/substrate oxidation? Determination by Mn X-ray absorption spectroscopy

Journal Article · Thu Jul 15 04:00:00 EDT 1999 · Journal of the American Chemical Society

OSTI ID:771800

Liang, Wenchuan ^[1]; Roelofs, Theo A; Cinco, Roehl M; Rompel, Annette; Latimer, Matthew J; Yu, Wa O; Sauer, Kenneth; Klein, Melvin P; Yachandra, Vittal K

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1. LBNL Library

The oxygen-evolving complex of photosystem II in plants and cyanobacteria catalyzes the oxidation of two water molecules to one molecule of dioxygen. A tetranuclear Mn complex is believed to cycle through five intermediate states (S0-S4) to couple the four-electron oxidation of water with the one-electron photochemistry occurring at the photosystem II reaction center. We have used X-ray absorption spectroscopy to study the local structure of the Mn complex and have proposed a model for it, based on studies of the Mn K-edges and the extended X-ray absorption fine structure of the S1 and S2 states. The proposed model consists of two di-mu-oxo bridged binuclear Mn units with Mn-Mn distances of {approximately}2.7 Angstrom that are linked to each other by a mono-mu-oxo bridge with a Mn-Mn separation of {approximately}3.3 Angstrom. The Mn-Mn distances are invariant in the S1 and S2 states. This report describes the application of X-ray absorption spectroscopy to S3 samples created under physiological conditions with saturating flash illumination. Significant changes are observed in the Mn-Mn distances in the S3 state compared to the S1 and the S2 states. The two 2.7 Angstrom Mn-Mn distances that characterize the di-mu-oxo centers are both lengthened to {approximately}2.8 and 3.0 Angstrom. The 3.3 Angstrom Mn-Mn and Mn-Ca distance also increases by 0.04-0.2 Angstrom. These changes in Mn-Mn distances are interpreted as consequences of the onset of substrate water oxidation in the S3 state. Mn-centered oxidation is evident during the S0 to S1 and S1 to S2 transitions. During the S2 to S3 transition, we propose that the changes in Mn-Mn distances are the consequence of ligand or water oxidation. Models that can account for such changes and the implications for the mechanism of water oxidation are discussed.

• Research Organization: Lawrence Berkeley National Lab., CA (US)
• Sponsoring Organization: USDOE Director, Office of Science. Office of Basic Energy Studies. Division of Energy Biosciences; National Institutes of Health (US)
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 771800
• Report Number(s): LBNL--45297
• Journal Information: Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Journal Issue: 14 Vol. 122; ISSN JACSAT; ISSN 0002-7863
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
ABSORPTION SPECTROSCOPY
CYANOBACTERIA
ENERGY-LEVEL TRANSITIONS
MANGANESE COMPLEXES
MOLECULAR MODELS
MORPHOLOGICAL CHANGES
OXIDATION
PHOTOCHEMISTRY
PHOTOSYSTEM II OXYGEN EVOLUTION MANGANESE X-RAY ABSORPTION SPECTROSCOPY
PLANTS
WATER
X-RAY SPECTROSCOPY