title: Low-temperature electron transfer suggests two types of Q(A) in intact photosystem II.
abstract: The correlation between the reduction of Q(A) and the oxidation of Tyr(Z) or Car/Chl(Z)/Cyt(b559) in spinach PSII enriched membranes induced by visible light at 10 K is studied by using electron paramagnetic resonance spectroscopy. Similar g=1.95-1.86 Q(A)(-*)EPR signals are observed in both Mn-depleted and intact samples, and both signals are long lived at low temperatures. The presence of PPBQ significantly diminished the light induced EPR signals from Q(A)(-*), Car(+*)/Chl(+*) and oxidized Cyt(b559), while enhancing the amplitude of the S(1)Tyr(Z)* EPR signal in the intact PSII sample. The quantification and stability of the g=1.95-1.86 EPR signal and signals arising from the oxidized Tyr(Z) and the side-path electron donors, respectively, indicate that the EPR-detectable g=1.95-1.86 Q(A)(-*) signal is only correlated to reaction centers undergoing oxidation of the side-path electron donors (Car/Chl(Z)/Cyt(b559)), but not of Tyr(Z). These results imply that two types of Q(A)(-*) probably exist in the intact PSII sample. The structural difference and possible function of the two types of Q(A) are discussed.
authors.affiliation: Laboratory of Photochemistry, Beijing National Laboratory of Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Han
authors.initials: H
authors.lastname: Bao
authors.forename: Chunxi
authors.initials: C
authors.lastname: Zhang
authors.forename: Yanan
authors.initials: Y
authors.lastname: Ren
authors.forename: Jingquan
authors.initials: J
authors.lastname: Zhao
mesh_terms: D016227:Benzoquinones / Q000737:chemistry* / Q000378:metabolism; D003080:Cold Temperature; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport; D007700:Kinetics; D010084:Oxidation-Reduction; D045332:Photosystem II Protein Complex / Q000737:chemistry* / Q000378:metabolism; D018724:Spinacia oleracea / Q000737:chemistry* / Q000378:metabolism; D014443:Tyrosine / Q000737:chemistry / Q000378:metabolism
chemical_list: D016227:Benzoquinones; D045332:Photosystem II Protein Complex; C025232:semiquinone radicals; D014443:Tyrosine