title: Differential mechanism of light-induced and oxygen-dependent restoration of the high-potential form of cytochrome b(559) in Tris-treated photosystem II membranes.
abstract: The effect of illumination and molecular oxygen on the redox and the redox potential changes of cytochrome b(559) (cyt b(559)) has been studied in Tris-treated spinach photosystem II (PSII) membranes. It has been demonstrated that the illumination of Tris-treated PSII membranes induced the conversion of the intermediate-potential (IP) to the reduced high-potential (HP(Fe2+)) form of cyt b(559), whereas the removal of molecular oxygen resulted in the conversion of the IP form to the oxidized high-potential (HP(Fe3+)) form of cyt b(559). Light-induced conversion of cyt b(559) from the IP to the HP form was completely inhibited above pH 8 or by the modification of histidine ligand that prevents its protonation. Interestingly, no effect of high pH or histidine modification was observed during the conversion of the IP to the HP form of cyt b(559) after the removal of molecular oxygen. These results indicate that conversion from the IP to the HP form of cyt b(559) proceeds via different mechanisms. Under illumination, conversion of the IP to the HP form of cyt b(559) depends primarily on the protonation of the histidine residue, whereas under anaerobic conditions, the conversion of the IP to the HP form of cyt b(559) is driven by higher hydrophobicity of the environment around the heme iron resulting from the absence of molecular oxygen.
authors.affiliation: Laboratory of Biophysics, Department of Experimental Physics, Faculty of Science, Palacký University, tr. 17. listopadu 1192/12, Olomouc, Czech Republic. pospip@prfnw.upol.cz
authors.forename: Pavel
authors.initials: P
authors.lastname: Pospísil
authors.forename: Arjun
authors.initials: A
authors.lastname: Tiwari
mesh_terms: D003573:Cytochrome b Group / Q000737:chemistry / Q000378:metabolism*; D005290:Ferric Compounds / Q000737:chemistry / Q000378:metabolism; D005296:Ferrous Compounds / Q000737:chemistry / Q000378:metabolism; D006639:Histidine / Q000737:chemistry / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008027:Light; D008956:Models, Chemical; D010084:Oxidation-Reduction / Q000187:drug effects / Q000528:radiation effects; D010100:Oxygen / Q000378:metabolism* / Q000494:pharmacology; D045332:Photosystem II Protein Complex / Q000737:chemistry / Q000378:metabolism*; D010940:Plant Proteins / Q000737:chemistry / Q000378:metabolism; D011199:Potentiometry; D013053:Spectrophotometry; D018724:Spinacia oleracea / Q000378:metabolism; D020524:Thylakoids / Q000187:drug effects / Q000378:metabolism* / Q000528:radiation effects; D014325:Tromethamine / Q000737:chemistry / Q000494:pharmacology
chemical_list: D003573:Cytochrome b Group; D005290:Ferric Compounds; D005296:Ferrous Compounds; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D014325:Tromethamine; D006639:Histidine; C019313:cytochrome b559; D010100:Oxygen