Identifying the lowest electronic states of the chlorophylls in the CP47 core antenna protein of photosystem II.
CP47 is a pigment-protein complex in the core of photosystem II that tranfers excitation energy to the reaction center. Here we report on a spectroscopic investigation of the isolated CP47 complex. By deconvoluting the 77 K absorption and linear dichroism, red-most states at 683 and 690 nm have been identified with oscillator strengths corresponding to approximately 3 and approximately 1 chlorophyll, respectively. Both states contribute to the 4 K emission, and the Stark spectrum shows that they have a large value for the difference polarizability between their ground and excited states. From site-selective polarized triplet-minus-singlet spectra, an excitonic origin for the 683 nm state was found. The red shift of the 690 nm state is most probably due to strong hydrogen bonding to a protein ligand, as follows from the position of the stretch frequency of the chlorophyll 13(1) keto group (1633 cm(-)(1)) in the fluorescence line narrowing spectrum at 4 K upon red-most excitation. We discuss how the 683 and 690 nm states may be linked to specific chlorophylls in the crystal structure [Zouni, A., Witt, H.-T., Kern, J., Fromme, P., Krauss, N., Saenger, W., and Orth, P. (2001) Nature 409, 739-743].
De Weerd
Frank L
FL
Faculty of Sciences, Division of Physics and Astronomy, Department of Biophysics and Physics of Complex Systems, Vrije Universiteit, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands. weerd@nat.vu.nl
Palacios
Miguel A
MA
Andrizhiyevskaya
Elena G
EG
Dekker
Jan P
JP
Van Grondelle
Rienk
R
D002734:Chlorophyll / Q000737:chemistry*; D005454:Fluorescence Polarization; D005615:Freezing; D045342:Light-Harvesting Protein Complexes; D018499:Linear Energy Transfer; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry*; D045332:Photosystem II Protein Complex; D013050:Spectrometry, Fluorescence; D013057:Spectrum Analysis; D018724:Spinacia oleracea
D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; C070970:photosystem II, chlorophyll-binding protein, CP-47; D002734:Chlorophyll