SPECTRA OF FLUORESCENCE LIFETIME AND INTENSITY OF Rhodopseudomonas sphaeroides AT ROOM AND LOW TEMPERATURE. COMPARISON BETWEEN THE WILD TYPE, THE C 71 REACTION CENTER‐LESS MUTANT AND THE B800–850 PIGMENT‐PROTEIN COMPLEX

Abstract

Spectra of the fluorescence lifetime and intensity of chromatophores from the wild type Rhodopseudomonas sphaeroides, from the C 71 reaction center-less mutant and of the B800-850 light harvesting pigment-protein complex have been studied by phase fluorimetry techniques at different light modulation frequencies at room and low temperature.As already known, closed reaction centers (saturating light) are still quenchers of antenna fluorescence although with a lower efficiency than when they are opened. The fluorescence yields and lifetimes of both the C 71 mutant strain and the B8W850complex are found to increase by about 30% between room and low temperature.The fluorescence lifetimes obtained for the C71 strain (0.65 ns at 20°C; 0.85 ns at 77 K) and for the 8850 complex (1 ns at 20°C; 1.3 ns at 77 K) indicate that the non-radiative deactivation pathways, in the antenna, remain important in the absence of the reaction centers even at low temperature. We suggest that these data arise from the presence of special antenna molecules which act as intrinsic quenchers of the B875 antenna fluorescence. Between room and low temperature, the fluorescence yield and lifetime of the wild type are found roughly constant. This result suggests that the energy trapping by the reaction centers is independent of the temperature. The mechanism governing the energy transfer from the antenna to the reaction centers may differ from the mechanism leading to the energy transfer within the antenna. We suggest that a partially irreversible trapping of the excitation energy, on its way to the reaction center, takes place in the vicinity of the reaction center.

Comparison of the fluorescence kinetics of detergent-solubilized and membrane-reconstituted LH2 complexes from Rps. acidophila and Rb. sphaeroides

“…sphaeroides show monoexponential decay kinetics with a fluorescence lifetime s f of 930 ps (Fig. 4a,b, open black circles), which is in agreement with results from previous studies performed at room temperature on LH2 complexes from this species (Monshouwer et al 1997;Sebban et al 1984;Chen et al 2005). Increasing the excitation density by a factor of three to 3Á10 13 photons/(pulseÁcm 2 ) resulted in the appearance of a second decay component s 2 of 50 ps and a decrease of the first component, s 1 , down to 800 ps (Fig.…”

“…acidophila and Rb. sphaeroides agree well with previously reported, room temperature fluorescence lifetimes for LH2 complexes of these species (Stiel et al 1997;Monshouwer et al 1997;Bopp et al 1997;Sebban et al 1984;Chen et al 2005). Longer fluorescence lifetimes have also been reported in the literature but those were usually measured at temperatures of 77 K or below (Freiberg et al 2003(Freiberg et al , 2004 and are thus not in conflict with the decay kinetics of the detergent-solubilized complexes that are reported here.…”

Energy migration in purple bacteria. The criterion for discrimination between migration- and trapping-limited photosynthetic units

“…Now let us estimate ~ = 3*. The K~ values were obtained in a number of experiments with purple bacteria (Godik and Borisov 1977) for Rhodospirillum rubrum (Sebban et al 1984), for Rhodobacter sphaeroides (Campillo et al 1977) and for RCfree mutant PM-8. It was measured in these works as 1.6 x 10 ° > K~ > 109s -1.…”

Energy transfer within the isolated B875 light‐harvesting pigment‐protein complex of Rhodobacter sphaeroides at 77 K studied by picosecond absorption spectroscopy

“…The presence of a special pigment component connecting the long wavelength antenna B875/B880 with the reaction center of purple bacteria has been proposed [1][2][3][4][5][6]. Fluorescence polarization at 4 K of the isolated B875 complex [7] was interpreted in terms of the existence of such an antenna pigment.…”