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DPA membranes from Allochromatium vinosum cells, in which carotenoid biosynthesis was inhibited using diphenylamine (DPA) were obtained, into which rhodopin was incorporated. The LH2 complex with rhodopin content of 85% was isolated. Using a test for the thermal stability of LH2 complexes (DPA and with incorporated rhodopin), it was established that carotenoids of the early stages of biosynthesis (≤1 molecules per complex) did not interfere with rhodopin incorporation. It was found that when the LH2 complex with incorporated rhodopin was irradiated with light at the wavelength of 502 nm, BChl850 was photobleached at a rate close to that in the control LH2 complex. This indicates that rhodopin, after being incorporated into the DPA LH2 complex, is capable of generating singlet oxygen under illumination. Previously obtained data on heterogeneity of the carotenoid composition in DPA LH2 complexes (variation in the number of individual carotenoids molecules per complex in the general population) and our earlier suggestion about the structural role of carotenoids, namely, their ability to stabilize the LH2 complexes, were confirmed. Based on analysis of our results, as well as of the literature data, the interaction of singlet oxygen and carotenoids is discussed. [ABSTRACT FROM AUTHOR]

The effect of the qualitative and quantitative content of carotenoids on the assembly of light-harvesting complexes isolated from the heat-resistant purple sulfur bacterium Thermochromatium (T.) tepidum was studied. To decrease the content of carotenoids in the photosynthetic membranes and complexes, an inhibitor of carotenonegesis, diphenylamine (DPA), was used. The minimum carotenoid content of 40% was observed in T. tepidum cells grown in the presence of 120 μM DPA. At higher DPA concentrations, the growth of the culture stopped. Photosynthetic membranes and LH2 and LH1-RC complexes were isolated from DPA-treated cells; carotenoid content of these structures was 45 and 55%, respectively. Their spectral characteristics in the near IR region did not depend on the amount of carotenoids in the complexes and were similar to those of the native wild-type complexes. Simultaneously with a general decrease in the content of carotenoids, carotenoids from earlier stages of biosynthesis, such as neurosporene, ζ-carotene, and their hydroxy derivatives, appeared in the DPA-treated complexes. Emergence in DPA-treated complexes of carotenoids with a shorter chain of conjugated double bonds than in the control resulted in an increase in the efficiency of energy transfer from carotenoids to bacteriochlorophyll. [ABSTRACT FROM AUTHOR]

The results of assembling the light-harvesting complexes in the cells of the purple sulfur bacterium Thiorhodospira (T.) sibirica strain Kir-3 while suppressing the biosynthesis of carotenoids with diphenylamine (DPA) were studied. LH2 complexes (B800-850 and B800-830) with different carotenoid composition were isolated from the cells obtained. Maximum inhibition of carotenoid biosynthesis (~90% of the control) was reached at an inhibitor concentration of 53.25 μM (9 mg/L). It was established that changes in the qualitative and quantitative composition of carotenoids do not affect the assembly of B800-830 and B800-850 complexes. It is assumed that, in the population of DPA-LH2 complexes from T. sibirica strain Kir-3, both the carotenoidless complexes and the complexes containing one or two carotenoid molecules can be assembled. These results support the hypothesis that carotenoids are not required for assembling B800-850 and B800-830 complexes. [ABSTRACT FROM AUTHOR]

Chromatophores and peripheral light-harvesting complexes B800–850 with a trace of carotenoids were isolated from Chromatium minutissimum cells in which carotenoid biosynthesis was inhibited by diphenylamine. Three methods previously used for the reconstitution of carotenoids into either the light-harvesting (LH1) type complexes or reaction centers (RC) of carotenoidless mutants were examined for the possibility of carotenoid reconstitution into the carotenoid depleted chromatophores. All these methods were found to be unsuitable because carotenoid depleted complex B800–850 from Chr. minutissimum is characterized by high lability. We have developed a novel method maintaining the native structure of the complexes and allowing reconstitution of up to 80% of the carotenoids as compared to the control. The reconstituted complex has a similar CD spectrum in the carotenoid region as the control, and its structure restores its stability. These data give direct proof for the structural role of carotenoids in bacterial photosynthesis. [ABSTRACT FROM AUTHOR]