PHOTOCHEMICAL HOLE-BURNING SPECTROSCOPY OF A PHOTOSYNTHETIC REACTION CENTER MUTANT WITH ALTERED CHARGE SEPARATION KINETICS - PROPERTIES AND DECAY OF THE INITIALLY EXCITED-STATE

被引:54
作者
MIDDENDORF, TR
MAZZOLA, LT
GAUL, DF
SCHENCK, CC
BOXER, SG
机构
[1] STANFORD UNIV, DEPT CHEM, STANFORD, CA 94305 USA
[2] COLORADO STATE UNIV, DEPT BIOCHEM, FT COLLINS, CO 80523 USA
关键词
D O I
10.1021/j100177a093
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
Photochemical hole-burning spectra have been obtained for the lowest energy electronic absorption band of the primary electron donor P of photosynthetic reaction centers (RCs) that exhibit different rates for the initial charge separation step. Wild type (WT) and Tyr(M)210 --> Phe mutant [(M)Y210F] RCs from Rhodobacter sphaeroides were studied at 1.5 K in 50% glycerol/buffer glasses. In both types of RC, difference spectra obtained by using narrow-bandwidth excitation on the low-energy edge of the P band display weak, narrow zero-phonon holes coincident with the laser wavelengths, in addition to a broad background bleach of much larger amplitude. The zero-phonon hole width in each type of RC corresponds quantitatively to the broadening expected from the excited-state lifetime. These results are inconsistent with electronic relaxation of the excited state of P prior to electron transfer. The agreement between the time- and frequency-domain experiments may result from vibrational thermalization prior to electron transfer. An alternative mechanism, which does not invoke subpicosecond vibrational thermalization and which is consistent with a wide range of data, is also presented. Quantitative estimates were obtained for the total electron-phonon coupling strength (Huang-Rhys factor) S and for the magnitudes of the homogeneous and inhomogeneous broadening in the P absorption band from self-consistent simulations of the 1.5 K absorption and hole spectra from a linear electron-phonon coupling model. The vibronic and line-width parameters deduced from the simulations are very similar for WT and (M)Y210F RCs.
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收藏
页码:10142 / 10151
页数:10
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