The manganese site of the photosynthetic oxygen-evolving complex probed by EPR spectroscopy of oriented photosystem II membranes: The g = 4 and g = 2 multiline signals

Journal Article · Tue Jan 21 04:00:00 EST 1992 · Biochemistry; (United States)

DOI:https://doi.org/10.1021/bi00117a034· OSTI ID:5618979

Kim, D H; Klein, M P; Sauer, K ^[1]; Britt, R D ^[2]

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1. Lawrence Berkeley Lab., Berkeley, CA (United States) Univ. of California, Berkeley (United States)
2. Univ. of California, Davis (United States)

The g = 4 and g = 2 multiline EPR signals arising from the Mn cluster of the photosynthetic oxygen-evolving complex (OEC) in the S{sub 2} state were studied in preparations of oriented photosystem II (PSII) membranes. The ammonia-modified forms of these two signals were also examined. The g = 4 signal obtained in oriented PSII membranes treated with NH{sub 4}Cl at pH 7.5 displays at least 16 partially resolved Mn hyperfine transitions with a regular spacing of 36 G. The observation of this g = 4 signal and is strongly suggestive of a model in which different spin state configurations of a single exchange-coupled Mn cluster give rise to the g = 4 and g = 2 multiline signals. A simulation shows the observed spectrum to be consistent with an S = 3/2 or S = 5/2 state of a tetranuclear Mn complex. The resolution of hyperfine structure on the NH{sub 3}-modified g = 4 signal is strongly dependent on sample orientation, with no resolved hyperfine structure when the membrane normal is oriented perpendicular to the applied magnetic field. The dramatic HN{sub 3}-induced changes in the g = 4 signal resolved in the spectra of oriented samples are suggestive that NH{sub 3} binding at the Cl{sup {minus}} site of the OEC may represent direct coordination of NH{sub 3} to the Mn cluster. Orientation dependence data on the g = 2 multiline signal show that hyperfine transitions in the wings of the signal are anisotropic.

• DOE Contract Number: AC03-76SF00098
• OSTI ID: 5618979
• Journal Information: Biochemistry; (United States), Journal Name: Biochemistry; (United States) Vol. 31:2; ISSN 0006-2960; ISSN BICHA
• Country of Publication: United States
• Language: English

Related Subjects

550200* -- Biochemistry
59 BASIC BIOLOGICAL SCIENCES
CHEMICAL REACTIONS
ELECTRON SPIN RESONANCE
EPR SPECTROMETERS
HYDROGEN COMPOUNDS
HYPERFINE STRUCTURE
MAGNETIC RESONANCE
MANGANESE COMPOUNDS
MEASURING INSTRUMENTS
MEMBRANES
OXIDATION
OXYGEN COMPOUNDS
PHOTOSYNTHETIC MEMBRANES
RESONANCE
SPECTROMETERS
TRANSITION ELEMENT COMPOUNDS
WATER