Energy transfer and charge separation in photosystem I:: P700 oxidation upon selective excitation of the long-wavelength antenna chlorophylls of Synechococcus elongatus

被引:154
作者
Pålsson, LO
Flemming, C
Gobets, B
van Grondelle, R
Dekker, JP
Schlodder, E
机构
[1] Tech Univ Berlin, Max Volmer Inst Biophys Chem & Biochem, D-10623 Berlin, Germany
[2] Free Univ Amsterdam, Dept Phys & Astron, Inst Mol Biol Sci, NL-1081 HV Amsterdam, Netherlands
关键词
D O I
10.1016/S0006-3495(98)77967-6
中图分类号
Q6 [生物物理学];
学科分类号
071011 ;
摘要
Photosystem I of the cyanobacterium Synechococcus elongatus contains two spectral pools of chlorophylls called C-708 and C-719 that absorb at longer wavelengths than the primary electron donor P700, We investigated the relative quantum yields of photochemical charge separation and fluorescence as a function of excitation wavelength and temperature in trimeric and monomeric photosystem I complexes of this cyanobacterium. The monomeric complexes are characterized by a reduced content of the C-719 spectral form. At room temperature, an analysis of the wavelength dependence of P700 oxidation indicated that all absorbed light, even of wavelengths of up to 750 nm, has the same probability of resulting in a stable P700 photooxidation, Upon cooling from 295 K to 5 K, the nonselectively excited steady-state emission increased by 11- and 16-fold in the trimeric and monomeric complexes, respectively, whereas the quantum yield of P700 oxidation decreased 2.2- and 1.7-fold. Fluorescence excitation spectra at 5 K indicate that the fluorescence quantum yield further increases upon scanning of the excitation wavelength from 690 nm to 710 nm, whereas the quantum yield of P700 oxidation decreases significantly upon excitation at wavelengths longer than 700 nm, Based on these findings, we conclude that at 5 K the excited state is not equilibrated over the antenna before charge separation occurs, and that similar to 50% of the excitations reach P700 before they become irreversibly trapped on one of the long-wavelength antenna pigments. Possible spatial organizations of the long-wavelength antenna pigments in the three-dimensional structure of photosystem I are discussed.
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页码:2611 / 2622
页数:12
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