Triplet-State Configurational Changes in Spheroidene Bound to the Reaction Center from Rb. sphaeroides 2.4.1 as revealed by Sub-microsecond Time-resolved Raman Spectroscopy at Room Temperature

Abstract

The possible mechanism of dissipation of triplet energy in reaction center (RC) bound carotenoid has been established by a pair of investigations which proposed that the series of configurational changes of carotenoid could facilitate the triplet-energy dissipation. The sub-microsecond time-resolved Raman spectra of spheroidene bound to the reduced RC of Rb. sphaeroides 2.4.1 were recorded at room temperature. The OD800 nm=100 cm^-1 sample with 100 mM ascorbate acid were pumped at 590 nm and probed at 532 nm respectively. After spectral analysis we observed a series of time-dependent spectral changes which could be attributed to the triplet-state configurational changes of the RC bound carotenoid. As strengthened by our preliminary study of time-resolved EPR spectroscopy (Yoshinori Kakitani, et. al., Biochemistry 2006, 45, 2053-2062), this investigation provided us the definitive evidence of the triplet-state configurational changes of the RC bound carotenoid functioned as the dissipation of triplet-energy under physiological temperature.