TY - JOUR
T1 - Temperature dependence of the reorganization energy for charge recombination in the reaction center from Rhodobacter sphaeroides
AU - Ortega, J. M.
AU - Mathis, P.
AU - Williams, Joann
AU - Allen, James
PY - 1996/3/19
Y1 - 1996/3/19
N2 - The rate of charge recombination from the primary quinone to the bacteriochlorophyll dimer of the reaction center from the photosynthetic purple bacterium Rhodobacter sphaeroides has been investigated using time- resolved optical spectroscopy. Measurements were performed at temperatures from 293 to 10 K on reaction centers that have specific mutations that result in a range of 425-780 meV for the free energy difference of charge recombination compared to 520 meV for wild type [Lin, X., Murchison, H. A., Nagarajan, V., Parson, W. W., Allen, J.P., and Williams, J. C. (1994) Proc. Natl. Acad. Sci. U.S.A. 91, 10265-10269]. In all cases the rate increased as the temperature decreased, although the details of the dependence were different for each mutant. The observed dependence of the rate upon temperature is modeled as arising principally from a several hundred meV change in reorganization energy. The relationships among the rate, temperature, and free energy differences can be well fit by a Marcus surface using two modes centered near 150 and 1600 cm-1 with a total reorganization energy that decreases from 930 to 650 meV as the temperature decreases from 293 to 10 K. In the inverted region, where the driving force is greater than the reorganization energy, the rate is found to be approximately independent of the free energy difference. This is modeled as due to the additional coupling of high frequency modes to the reaction. An alternative model is also considered in which a 140 meV increase in the reorganization energy is matched by a 140 meV increase in the free energy difference as the temperature decreases. The possible role of solvent dipoles in determining this temperature dependence of the reorganization energy and the implications for other electron transfer reactions are discussed.
AB - The rate of charge recombination from the primary quinone to the bacteriochlorophyll dimer of the reaction center from the photosynthetic purple bacterium Rhodobacter sphaeroides has been investigated using time- resolved optical spectroscopy. Measurements were performed at temperatures from 293 to 10 K on reaction centers that have specific mutations that result in a range of 425-780 meV for the free energy difference of charge recombination compared to 520 meV for wild type [Lin, X., Murchison, H. A., Nagarajan, V., Parson, W. W., Allen, J.P., and Williams, J. C. (1994) Proc. Natl. Acad. Sci. U.S.A. 91, 10265-10269]. In all cases the rate increased as the temperature decreased, although the details of the dependence were different for each mutant. The observed dependence of the rate upon temperature is modeled as arising principally from a several hundred meV change in reorganization energy. The relationships among the rate, temperature, and free energy differences can be well fit by a Marcus surface using two modes centered near 150 and 1600 cm-1 with a total reorganization energy that decreases from 930 to 650 meV as the temperature decreases from 293 to 10 K. In the inverted region, where the driving force is greater than the reorganization energy, the rate is found to be approximately independent of the free energy difference. This is modeled as due to the additional coupling of high frequency modes to the reaction. An alternative model is also considered in which a 140 meV increase in the reorganization energy is matched by a 140 meV increase in the free energy difference as the temperature decreases. The possible role of solvent dipoles in determining this temperature dependence of the reorganization energy and the implications for other electron transfer reactions are discussed.
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U2 - 10.1021/bi952882y
DO - 10.1021/bi952882y
M3 - Article
C2 - 8639484
AN - SCOPUS:0029940149
SN - 0006-2960
VL - 35
SP - 3354
EP - 3361
JO - Biochemistry
JF - Biochemistry
IS - 11
ER -