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The S1 split signal of photosystem II; a tyrosine-manganese coupled interaction |
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| Authors: | Nicholas Cox,Naray Pewnim,Paul J. Smith,Joseph L. Hughes,Stenbjö rn Styring,Ron J. Pace |
| Affiliation: | a Department of Chemistry, College of Science, Australian National University, Canberra, ACT 0200, Australia b Department of Photochemistry and Molecular Science, Ångström Laboratory, Uppsala University, P.O. Box 523, SE-751 20, Uppsala, Sweden c Research School of Chemistry, Australian National University, Canberra, ACT 0200, Australia |
| Abstract: | Detailed optical and EPR analyses of states induced in dark-adapted PS II membranes by cryogenic illumination permit characterization and quantification of all pigment derived donors and acceptors, as well as optically silent (in the visible, near infrared) species which are EPR active. Near complete turnover formation of QA− is seen in all centers, but with variable efficiency, depending on the donor species. In minimally detergent-exposed PS II membranes, negligible (< 5%) oxidation of chlorophyll or carotenoid centers occurs for illumination temperatures 5-20 K. An optically silent electron donor to P680+ is observed with the same decay kinetics as the S1 split signal. Cryogenic donors to P680+ seen are: (i) transient (t1/2 ∼ 150 s) tyrosine related species, including ‘split signals’ (∼ 15% total centers), (ii) reduced cytochrome b559 (∼ 30-50% centers), and (iii) an organic donor, possibly an amino acid side chain, (∼ 30% centers). |
| Keywords: | EPR, Electron Paramagnetic Resonance PS II, Photosystem II OEC, Oxygen Evolving Complex QA, primary plastoquinone A acceptor of PS II YZ, tyrosine Z or residue 161 of the D1 polypeptide of PS II YD, tyrosine D or residue 161 of the D2 polypeptide of PS II Pheo, pheophytin CW, continuous wave ZFS, zero field splitting MA, modulation amplitude NIR, near infrared chl, chlorophyll Tris, Tris(hydroxymethyl)aminomethane PpBQ, Phenyl-p-benzoquinone |
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