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| - HYSCORE Spectroscopy in the Cytochrome b559 of thePhotosystem II Reaction Center
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| - A HYSCORE investigation of the heme center in the cytochrome b559 is presented. To assignthe observed signals to specific nuclei, bis-imidazol coordinated heme compounds that model the ironenvironment in cytochrome b559 are also studied. In the model compounds selective isotopic substitutionof nitrogen atoms has been performed. The HYSCORE spectra allow us to obtain the hyperfine andquadrupolar coupling tensors of heme and imidazol bonding nitrogen atoms. The results can be interpretedin terms of the structure and the electronic distribution of the active center. The hyperfine tensors indicatethat the unpaired electron is confined in a nonbonding iron orbital with a negligible nitrogen p orbitalcontribution. Quadrupolar coupling tensors suggest that the orientation of the semioccupied orbital is drivenby the orientation of the two parallel imidazol rings of the axial histidine side chains. The results are discussedin terms of the structure−function relationship of cytochromes.
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