In aqueous solutions of chlorophyll (Chl) a with synthesized polypeptides, at high ratios of Chl to polypeptides (about 75-150 µM to 500 µM) clusters of polypeptides and pigment molecules were formed. The main absorption maxima of more than one formed cluster were located at about 500 nm (Soret band) and in the region of 720-806 nm (red band). The formation of these clusters was fairly slow (some hours) at room temperature and even slower at 4 °C. The rate of cluster formation increased with the increase in Chl concentration. The addition of the even low amount of reaction centres (RCs), separated from the purple bacteria Rhodobacter sphaeroides, to the sample of Chl with polypeptides caused a very strong decrease in the efficiency of cluster formation, and a change in concentration ratios of various pigment-polypeptide aggregates. It was probably a competition between the interaction of Chl with polypeptides and with the RCs. The yield of thermal deactivation of the clusters was high, much higher than that for the RCs alone and it was different for various types of cluster. The clusters absorbing at 725-750 nm were fluorescent with maximum of emission at about 770 nm, whereas clusters absorbing at about 800 nm were nonfluorescent. and H. Enomoto ... [et al.].
Reaction centres (RC) from the purpie bacterium Rhodohacter sphaeroides (strain R-24.1 and carotenoid-free mutant R-26.1) were separated and immobilized in isotropic and stretched polyvinyl alcohol (PVA) films. Absorption, fluorescence, delayed luminescence (8-300 K) and photoacoustic spectra (PAS) of immobilized samples were measured. The RC from wild strain R-24.1 and ffom carotenoid-free mutant R-26.1 were differently oriented in the stretched polymer film. In R-24.1 the long axis of the RC complex was directed under some angle with respect to the perpendicular direction to the PVA film plane, whereas in R-26.1 it was almost perpendicular to this plane. The shapes of linear dichroism (LD) of both strains were different. Delayed luminescence (DL) bands were located in a similar wavelength range as the bacteriochlorophyll and bacteriopheophytin prompt fluorescence bands. Intensity of DL was independent of temperature in the 8-300 K range. The intensity of DL was about three time lower than that of the fluorescence. The dependence of PAS on the frequency of radiation modulation and on the phase shift between modulated acting radiation and measured PAS showed that part of the thermal deactivation was undergoing slowly. Intensity ratio of the slow component to the fast one and/or decay time of the slow component of thermal deactivation were different for various chromophores and for RC ffom the two strains of bacteria.
Absorption , fluorescence, delayed emission and photoacoustic spectra were obtained for the green photosynthetic bacterium. Whole cells incorporated in fluid (culture medium, viscous solution of polyvinyl alcohol, glycol) and rigid (isotropic and stretched polyvinyl alcohol film) media were investigated. The polarized absorption spectra of the stretched polyvinyl alcohol sample showed that the Qy transition moments of chlorosomal bacteriochlorophyll с was almost parallel to the film axis. Bacteriochlorophyll (BChl) с degradation occurred in some of the samples during prolonged storage and as a result a pigment absorbing at 670 nm, which was disaggregated BChl с or/and bacteriopheophytin c, was formed. This pigment was unoriented in stretched polyvinyl alcohol. The fluorescence spectrum of native cells can be analyzed using three Gaussian components at 754, 781 and 813 pm. The first component seems to be related to BChl с aggregates and the others to BChl a complexes. The time-resolved delayed luminescence spectra showed that practically all the complexes of green bacteria exhibited delayed emission but the decay times and intensities were different for the different complexes. In the photoacoustic spectra two maxima of the chlorosomal BChl с forms were well resolved and located at 748 and 765 nm. The photoacoustic maximum at 830 nm was probably related to the reaction centre (RC). In the Soret band the largest peak of the photoacoustic spectra was observed at 473 nm which showed that carotenoids absorbing in this range were losing more excitation by heat. The BChl с aggregates attached to chlorosome rods exhibited a peak at 446 nm. The efficient thermal deactivation also showed a BChl a located in RC (peak at 846 nm) and long-wavelength BChl a antenna complexes with a deactivation peak at 884 nm.