Optical Spectra of Synechocystis and Spinach Photosystem II Preparations at 1.7 K: Identification of the D1-Pheophytin Energies and Stark Shifts
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- 作者：Sindra Peterson Å ; rskö ; ld ; Vanessa M. Masters ; Barry J. Prince ; Paul J. Smith ; Ron J. Pace ; and Elmars Krausz
- 刊名：Journal of the American Chemical Society
- 出版年：2003
- 出版时间：October 29, 2003
- 年：2003
- 卷：125
- 期：43
- 页码：13063 - 13074
- 全文大小：363K
- 年卷期：v.125,no.43(October 29, 2003)
- ISSN：1520-5126
文摘
We report and compare highly resolved, simultaneously recorded absorption and CD spectra ofactive Photosystem II (PSII) samples in the range 440-750 nm. From an appropriately scaled comparisonof spinach membrane fragment (BBY) and PSII core spectra, we show that key features of the core spectrumare quantitatively represented in the BBY data. PSII from the cyanobacterium Synechocystis 6803 displayspectral features in the Qy region of comparable width (50-70 cm-1 fwhm) to those seen in plant PSII butthe energies of the resolved features are distinctly different. A comparison of spectra taken of PSII poisedin the S1QA and S2QA- redox states reveals electrochromic shifts largely attributable to the influence ofQA- on PheoD1. This allows accurate determinations of the PheoD1 Qy absorption positions to be at 685.0nm for spinach cores, 685.8 nm for BBY particles, and 683.0 nm for Synechocystis. These are discussedin terms of earlier reports of the PheoD1 energies in PSII. The Qx transition of PheoD1 undergoes a blueshift upon QA reduction, and we place a lower limit of 80 cm-1 on this shift in plant material. By comparingthe magnitude of the Stark shifts of the Qx and Qy bands of PheoD1, the directions of the transition-induceddipole moment changes, 
x and y, for this functionally important pigment could be determined, assumingnormal magnitudes of the 's. Consequently, x and y are determined to be approximately orthogonalto the directions expected for these transitions. Low-fluence illumination experiments at 1.7 K resulted invery efficient formation of QA-. This was accompanied by cyt b559 oxidation in BBYs and carotenoid oxidationin cores. No chlorophyll oxidation was observed. Our data allow us to estimate the quantum efficiency ofPSII at this temperature to be of the order 0.1-1. No Stark shift associated with the S1-to-S2 transition ofthe Mn cluster is evident in our samples. The similarity of Stark data in plants and Synechocystis points tominimal interactions of PheoD1 with nearby chloropyll pigments in active PSII preparations. This appearsto be at variance with interpretations of experiments performed with inactive solubilized reaction-centerpreparations.
x and y, for this functionally important pigment could be determined, assumingnormal magnitudes of the 's. Consequently, x and y are determined to be approximately orthogonalto the directions expected for these transitions. Low-fluence illumination experiments at 1.7 K resulted invery efficient formation of QA-. This was accompanied by cyt b559 oxidation in BBYs and carotenoid oxidationin cores. No chlorophyll oxidation was observed. Our data allow us to estimate the quantum efficiency ofPSII at this temperature to be of the order 0.1-1. No Stark shift associated with the S1-to-S2 transition ofthe Mn cluster is evident in our samples. The similarity of Stark data in plants and Synechocystis points tominimal interactions of PheoD1 with nearby chloropyll pigments in active PSII preparations. This appearsto be at variance with interpretations of experiments performed with inactive solubilized reaction-centerpreparations.