title: Species-dependence of the redox potential of the primary quinone electron acceptor QA in photosystem II verified by spectroelectrochemistry.
abstract: The redox potentials E(m)(Q(A)/Q(A)(-)) of the primary quinone electron acceptor Q(A) in oxygen-evolving photosystem II complexes of three species were determined by spectroelectrochemistry. The E(m)(Q(A)/Q(A)(-)) values were experimentally found to be -162+/-3 mV for a higher plant spinach, -171+/-3 mV for a green alga Chlamydomonas reinhardtii and -104+/-4 mV vs. SHE for a red alga Cyanidioschyzon merolae. On the basis of possible deviations for the experimental values, as estimated to differ by 9-29 mV from each true value, plausible causes for such remarkable species-dependence of E(m)(Q(A)/Q(A)(-)) are discussed, mainly by invoking the effects of extrinsic subunits on the delicate structural environment around Q(A).
authors.affiliation: Institute of Industrial Science, The University of Tokyo, Tokyo, Japan.
authors.forename: Tadao
authors.initials: T
authors.lastname: Shibamoto
authors.forename: Yuki
authors.initials: Y
authors.lastname: Kato
authors.forename: Ryo
authors.initials: R
authors.lastname: Nagao
authors.forename: Takuya
authors.initials: T
authors.lastname: Yamazaki
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Tomo
authors.forename: Tadashi
authors.initials: T
authors.lastname: Watanabe
mesh_terms: D016227:Benzoquinones / Q000378:metabolism*; D016825:Chlamydomonas reinhardtii / Q000201:enzymology; D004563:Electrochemistry; D004579:Electron Transport; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000378:metabolism*; D000461:Rhodophyta / Q000201:enzymology; D013045:Species Specificity; D013050:Spectrometry, Fluorescence; D018724:Spinacia oleracea / Q000201:enzymology
chemical_list: D016227:Benzoquinones; D045332:Photosystem II Protein Complex; C004532:quinone; D010100:Oxygen