title: HYSCORE spectroscopy in the cytochrome b(559) of the photosystem II reaction center.
abstract: A HYSCORE investigation of the heme center in the cytochrome b(559) is presented. To assign the observed signals to specific nuclei, bis-imidazol coordinated heme compounds that model the iron environment in cytochrome b(559) are also studied. In the model compounds selective isotopic substitution of nitrogen atoms has been performed. The HYSCORE spectra allow us to obtain the hyperfine and quadrupolar coupling tensors of heme and imidazol bonding nitrogen atoms. The results can be interpreted in terms of the structure and the electronic distribution of the active center. The hyperfine tensors indicate that the unpaired electron is confined in a nonbonding iron orbital with a negligible nitrogen p orbital contribution. Quadrupolar coupling tensors suggest that the orientation of the semioccupied orbital is driven by the orientation of the two parallel imidazol rings of the axial histidine side chains. The results are discussed in terms of the structure-function relationship of cytochromes.
authors.affiliation: Instituto de Ciencia de Materiales de Aragón, Consejo Superior de Investigaciones Científicas, Universidad de Zaragoza, Plaza S. Francisco s/n, E-50009 Zaragoza, Spain.
authors.forename: Inés
authors.initials: I
authors.lastname: García-Rubio
authors.forename: Jesús I
authors.initials: JI
authors.lastname: Martínez
authors.forename: Rafael
authors.initials: R
authors.lastname: Picorel
authors.forename: Inmaculada
authors.initials: I
authors.lastname: Yruela
authors.forename: Pablo J
authors.initials: PJ
authors.lastname: Alonso
mesh_terms: D003573:Cytochrome b Group / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D006418:Heme / Q000737:chemistry; D045332:Photosystem II Protein Complex / Q000737:chemistry*; D010940:Plant Proteins / Q000737:chemistry; D011487:Protein Conformation; D018724:Spinacia oleracea / Q000737:chemistry
chemical_list: D003573:Cytochrome b Group; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D006418:Heme; C019313:cytochrome b559