Selective replacement of the active and inactive pheophytin in reaction centres of Photosystem II by 131-deoxo-131-hydroxy-pheophytin a and comparison of their 6 K absorption spectra |
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Authors: | Germano M Shkuropatov AYa Permentier H Khatypov RA Shuvalov VA Hoff AJ Van Gorkom HJ |
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Institution: | (1) Biophysics Department, Huygens Laboratory, Leiden University, P.O. Box 9504, 2300 RA Leiden, The Netherlands;(2) Institute of Basic Biological Problems, Russian Academy of Sciences, Pushchino, Moscow Region, 142290, Russian Federation;(3) Biophysics Department, Huygens Laboratory, Leiden University, P.O. Box 9504, 2300 RA Leiden, The Netherlands |
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Abstract: | Pheophytin a (Pheo) in Photosystem II reaction centres was exchanged for 131-deoxo-131-hydroxy-pheophytin a (131-OH-Pheo). The absorption bands of 131-OH-Pheo are blue-shifted and well separated from those of Pheo. Two kinds of modified reaction centre preparations can be
obtained by applying the exchange procedure once (RC1×) or twice (RC2×). HPLC analysis and Pheo QX absorption at 543 nm show that in RC1× about 50% of Pheo is replaced and in RC2× about 75%. Otherwise, the pigment and protein composition are not modified. Fluorescence emission and excitation spectra
show quantitative excitation transfer from the new pigment to the emitting chlorophylls. Photoaccumulation of Pheo− is unmodified in RC1× and decreased only in RC2×, suggesting that the first exchange replaces the inactive and the second the active Pheo. Comparing the effects of the first
and the second replacement on the absorption spectrum at 6 K did not reveal substantial spectral differences between the active
and inactive Pheo. In both cases, the absorption changes in the QY region can be interpreted as a combination of a blue shift of a transition at 684 nm, a partial decoupling of chlorophylls
absorbing at 680 nm and a disappearance of Pheo absorption in the 676-680 nm region. No absorption decrease is observed at
670 nm for RC1× or RC2×, showing that neither of the two reaction centre pheophytins contributes substantially to the absorption at this wavelength.
This revised version was published online in June 2006 with corrections to the Cover Date. |
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Keywords: | Photosystem II pheophytin a pigment exchange reaction centre 131-deoxo-131-hydroxy pheophytin a |
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