Abstract
Carotenoid (Car) in the reaction center (RC) plays the function of photo-protection (i.e., triplet-energy dissipation). In the RC, a series of electron-transfer reaction is started by the charge separation, and this must influence the redox potential of the environment. From this viewpoint, we determined the lifetime of triplet Car in the RC, and examined if it is affected by the addition of a reducing agent. In the experiment, we excited the special-pair bacteriochlorophyll in RC from Rhodobactor sphaeroides 2.4.1 to the Qy state, and measured the submicrosecond time-resolved absorption spectra. On increasing of the amount of sodium ascorbate, the signal of triplet Car was increased, and the triplet-state lifetime of Car was decreased systematically. The results show that the decay rate of triplet state is enhanced depending on the amount of triplet state generated. We are planning to examine the case of Rhodospirillum rubrum S1, as well.
