title: Electrogenicity of electron and proton transfer at the oxidizing side of photosystem II.
abstract: The electrogenicity of electron and proton transfer at the oxidizing side of PSII was monitored by transmembrane electrochromism of carotenoids in thylakoids and, independently, by electrometry in oxygen-evolving photosystem II core particles. It yielded dielectrically weighted distances between cofactors. They were related to the one between YZox and QA- (=100%). The electron transfer from YZ to P680+ ranged over a relative distance of 15%, while the one from Mn4 to YZox ranged over less than 3.5%. The latter result placed Mn4 and YZ at about the same weighted depth in the membrane. The oxidation of cofactor X by YZox during S2 --> S3 ranged over 10%. We tentatively attributed 7% to proton transfer into the lumen and 3% to electron transfer, in line with our notion that one proton is liberated from Xox itself. This placed X at the same depth in the membrane as Mn. Proton release upon the final oxidation of water during the oxygen-evolving step S4 --> S0 revealed relative electrogenic components of 5.5% in core particles and between 10.5% (pH 7.4) and 2% (pH 6.2) in thylakoids. The former likely reflected proton transfer from bound water into the lumen and the latter to intraprotein bases that were created in the foregoing transitions. A tentative scheme for the arrangement of cofactors at the oxidizing side of photosystem II is presented.
authors.affiliation: Abteilung Biophysik, FB Biologie/Chemie, Universität Osnabrück, D-49069 Osnabrück, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Haumann
authors.forename: A
authors.initials: A
authors.lastname: Mulkidjanian
authors.forename: W
authors.initials: W
authors.lastname: Junge
mesh_terms: D002338:Carotenoids / Q000378:metabolism; D004563:Electrochemistry; D004583:Electrons; D007425:Intracellular Membranes / Q000378:metabolism; D007700:Kinetics; D008081:Liposomes; D010084:Oxidation-Reduction; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism*; D045332:Photosystem II Protein Complex; D011522:Protons
chemical_list: D008081:Liposomes; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D011522:Protons; D002338:Carotenoids