| The cytochrome b6f (Cyt b6f) complex is one of the three integrate membrane protein complex in the photosynthetic electron transport chain. According to the X-ray structure analysis (Kurisu et al, 2003; Stroebel et al, 2003), one chlorophyll a (Chl a ) molecule is bound between helices F and G of subunit IV of this complex. The Chl a in the complex, however, has a smaller excited-state life time, most probably dued to quenching by the electron exchange between the Chl a and nearby amino acid(Tyr105 of Cyt b6), than that of free Chl a in methanol(~4ns), and thus reduces the formation of the Chl a triplet state (Dashdorj et al, 2005). This is considered as one kind of protection mechanism of the Chl a against singlet oxygen in the complex although there are not any evidences for the mechanism still. Also, the role(s) of this Chl a remains unclear. In this work, the excited-state life time of Chl a in the Cyt b6f from spinach was determined, the quenching mechanism of the excited state of Chl a in the complex was investigated, and the function of the Chl a was also proposed based on some experiments data.1. Different excited-state life times of Chl a in different Cyt b6f sources were obtained in some reports. But the two detergents, n-Dodecylβ-D-maltoside (DDM) and n-Octylβ-D-glucopyranoside (β-OG),were used respectively in the reports. So the effects of the two detergents on the structure and function of the Cyt b6f were investigated by stead-state absorption, fluorescence, CD, dynamic light scattering, and time-resolved absorption spectroscopy in this work firstly. The results are as follows: the DDM detergent dissolves the Cyt b6f better thanβ-OG detergent does; DDM can keep the Cyt b6f in native state, under which the hemes and Chl a experience specific environment, while theβ-OG make the complex in denatured state in some sort, under which the catalyzed electron transfer activity of the complex...
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