title: Redox potential of cytochrome c550 in the cyanobacterium Thermosynechococcus elongates.
abstract: Cytochrome c550 (cyt c550) from photosystem II (PSII) exists in the PSII-bound form but can be released from PSII by treatment with divalent cations or Tris, yielding the isolated form. We calculated heme redox potentials (Em) based on the crystal structures of cyt c550 by solving the Poisson-Boltzmann equation. In the isolated form, the calculated Em are -240 mV at pH 6.0 and -352 mV at pH 9.0. This pH-dependence is predominantly due to deprotonation of the heme-propionic group near Asn-49. In the PSII-bound form, the calculated E(m) was up-shifted by 160 mV versus the isolated form due to a conformational change of protein backbone, yielding Em=-84 mV.
authors.affiliation: Institute of Chemistry, Department of Biology, Chemistry, and Pharmacy, Free University of Berlin, Takustrasse 6, D-14195 Berlin, Germany.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ishikita
authors.forename: Ernst-Walter
authors.initials: EW
authors.lastname: Knapp
mesh_terms: D000458:Cyanobacteria / Q000201:enzymology / Q000302:isolation & purification / Q000378:metabolism*; D003574:Cytochrome c Group / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D006418:Heme / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D010084:Oxidation-Reduction; D045332:Photosystem II Protein Complex / Q000378:metabolism
chemical_list: D003574:Cytochrome c Group; D045332:Photosystem II Protein Complex; D006418:Heme; C031732:cytochrome C-550