rhodovibrin and rhodopin

Effect of illumination intensity and inhibition of carotenoid biosynthesis on assemblage of different spectral types of LH2 complexes in a purple sulfur bacterium Allochromatium (Alc.) vinosum ATCC 17899 was studied. Under illumination of 1200 and 500 lx, the complexes B800-850 and B800-840 and B800-820 were assembled. While rhodopine was the major carotenoid in all spectral types of the LH2 complex, a certain- increase in the content of carotenoids with higher numbers of conjugated double bonds (anhydrorhodovibrin and didehydrorhodovibrin) was observed in the B800-820 complex. At 1200 lx, the cells grew slowly at diphe- nylamine (DPA) concentrations not exceeding 53 .iM, while at illumination intensity decreased to 500 Ix they could grow at 71 jiM DPA (DPA cells). Independent on illumination level, the inhibitor is supposed to impair the functioning of phytoine synthetase (resulting in a decrease in the total carotenoid content) and of phyto- ine desturase, which results in formation of neurosporene hydroxy derivatives and ;-carotene. In the cells grown at 500 lx, small amounts of spheroidene and.OH-spheroidene were detected. These carotenoids were originally found under conditions of carotenoid synthesis inhibition in bacteria with spirilloxanthin as the major carotenoid. Carotenoid content in the LH2 complexes isolated from the DPA cells was -15% of the control (without inhibition) for the B800-850 and -20%of the control for the B800-820 and B800-840 DPA complexes. Compared to the DPA pigment-containing membranes, the DPA complexes were enriched with -carotenoids due to- disintegration of some carotenoid-free complexes in the course of isolation. These results support the supposition that some of the B800-820, B800-840, and B800-850 complexes may be Assembled in the cells of Alc. vinosum ATCC 17899 without carotenoids. Comparison of the characteristics obtained for Alc. vinosum ATCC 17899 and the literature data on strain D of the same bacteria shows that they belong to two different strains, rather than to one as was previously supposed.

Topics: Bacterial Proteins; Carotenoids; Chromatiaceae; Culture Media; Diphenylamine; Dose-Response Relationship, Radiation; Gene Expression; Ligases; Light; Light-Harvesting Protein Complexes; Mixed Function Oxygenases; Xanthophylls; zeta Carotene

The crtD gene of the purple bacterium Rhodospirillum rubrum, encoding rhodopin desaturase, was cloned into a broad-host range expression plasmid (pRKCAG53) and transferred to the R. rubrum crtD(-) mutant, ST4, which restored the wild-type phenotype and produced the carotenoid spirilloxanthin. pRKCAG53 was randomly mutated in an Escherichia coli mutator strain and then transferred to ST4 for selection of non-wild-type phenotypes. Strains containing the mutated expression plasmid exhibited two coloured phenotypes: a "brown" phenotype, corresponding to 3,4,3',4'-tetrahydrospirilloxanthin, arising from plasmids containing an inactivated crtD gene, and secondly, a "dark pink" phenotype. Absorption and mass spectra and HPLC analysis obtained from hexane extracts of brown mutants, confirmed the carotenoid assignment above. DNA sequence analysis of the crtD genes from the brown transconjugants showed frameshifts at the extreme C-terminus, suggesting that this domain forms part of the active site. Spectral analysis of the dark pink strains showed an additional, non-natural double bond formed at the carotenoid end, yielding the asymmetric carotenoids, 3,4,3',4'-tetradehydrorhodopin - and 3',4'-didehydroanhydrorhodovibrin, each containing 14 conjugated double bonds. For only two dark pink strains, was a mutation in crtD detected, in both cases at the N-terminus of CrtD. Otherwise, the higher conjugation was ascribed to an elevated plasmid copy number.

Topics: Carotenoids; Cloning, Molecular; Frameshift Mutation; Gene Expression; Genetic Engineering; Mutagenesis; Oxidoreductases; Phenotype; Rhodospirillum rubrum; Sequence Analysis, DNA

The light-harvesting complex 2 from the thermophilic purple bacterium Thermochromatium tepidum was purified and studied by steady-state absorption and fluorescence, sub-nanosecond-time-resolved fluorescence and femtosecond time-resolved transient absorption spectroscopy. The measurements were performed at room temperature and at 10 K. The combination of both ultrafast and steady-state optical spectroscopy methods at ambient and cryogenic temperatures allowed the detailed study of carotenoid (Car)-to-bacteriochlorophyll (BChl) as well BChl-to-BChl excitation energy transfer in the complex. The studies show that the dominant Cars rhodopin (N=11) and spirilloxanthin (N=13) do not play a significant role as supportive energy donors for BChl a. This is related with their photophysical properties regulated by long π-electron conjugation. On the other hand, such properties favor some of the Cars, particularly spirilloxanthin (N=13) to play the role of the direct quencher of the excited singlet state of BChl.

Topics: Bacteriochlorophylls; Carotenoids; Chromatiaceae; Cold Temperature; Energy Transfer; Kinetics; Light; Light-Harvesting Protein Complexes; Photosynthesis; Spectrometry, Fluorescence; Temperature; Time Factors; Xanthophylls