bacteriochlorophylls
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Chlorosomes from green photosynthetic bacteria are large photosynthetic antennae containing self-assembling aggregates of bacteriochlorophyll c, d, or e. The pigments within chlorosomes are organized in curved lamellar structures. Aggregates with similar optical properties can be prepared in vitro, both in polar as well as non-polar solvents. In order to gain insight into their structure we examined hexane-induced aggregates of purified bacteriochlorophyll c by X-ray scattering. The bacteriochlorophyll c aggregates exhibit scattering features that are virtually identical to those of native chlorosomes demonstrating that the self-assembly of these pigments is fully encoded in their chemical structure. Thus, the hexane-induced aggregates constitute an excellent model to study the effects of chemical structure on assembly. Using bacteriochlorophyllides transesterified with different alcohols we have established a linear relationship between the esterifying alcohol length and the lamellar spacing. The results provide a structural basis for lamellar spacing variability observed for native chlorosomes from different species. A plausible physiological role of this variability is discussed. The X-ray scattering also confirmed the assignments of peaks, which arise from the crystalline baseplate in the native chlorosomes.
- MeSH
- alkoholy chemie MeSH
- anizotropie MeSH
- bakteriochlorofyly chemie metabolismus MeSH
- buněčné struktury metabolismus MeSH
- Chlorobium metabolismus MeSH
- esterifikace MeSH
- hexany chemie MeSH
- kvarterní struktura proteinů MeSH
- radiační rozptyl MeSH
- rentgenové záření MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Chlorosomes, the light-harvesting antennae of green photosynthetic bacteria, are based on large aggregates of bacteriochlorophyll molecules. Aggregates with similar properties to those in chlorosomes can also be prepared in vitro. Several agents were shown to induce aggregation of bacteriochlorophyll c in aqueous environments, including certain lipids, carotenes, and quinones. A key distinguishing feature of bacteriochlorophyll c aggregates, both in vitro and in chlorosomes, is a large (>60 nm) red shift of their Q(y) absorption band compared with that of the monomers. In this study, we investigate the self-assembly of bacteriochlorophyll c with the xanthophyll astaxanthin, which leads to the formation of a new type of complexes. Our results indicate that, due to its specific structure, astaxanthin molecules competes with bacteriochlorophylls for the bonds involved in the aggregation, thus preventing the formation of any significant red shift compared with pure bacteriochlorophyll c in aqueous buffer. A strong interaction between both the types of pigments in the developed assemblies, is manifested by a rather efficient (~40%) excitation energy transfer from astaxanthin to bacteriochlorophyll c, as revealed by fluorescence excitation spectroscopy. Results of transient absorption spectroscopy show that the energy transfer is very fast (<500 fs) and proceeds through the S(2) state of astaxanthin.
- MeSH
- bakteriální proteiny chemie izolace a purifikace metabolismus MeSH
- bakteriochlorofyly chemie izolace a purifikace metabolismus MeSH
- Chlorobium chemie MeSH
- fotosyntéza MeSH
- přenos energie * MeSH
- spektrální analýza MeSH
- světlo MeSH
- světlosběrné proteinové komplexy chemie metabolismus MeSH
- xanthofyly chemie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Chlorosomes from green photosynthetic bacteria belong to the most effective light-harvesting antennas found in nature. Quinones incorporated in bacterichlorophyll (BChl) c aggregates inside chlorosomes play an important redox-dependent photo-protection role against oxidative damage of bacterial reaction centers. Artificial BChl c aggregates with and without quinones were prepared. We applied hole-burning spectroscopy and steady-state absorption and emission techniques at 1.9 K and two different redox potentials to investigate the role of quinones and redox potential on BChl c aggregates at low temperatures. We show that quinones quench the excitation energy in a similar manner as at room temperature, yet the quenching process is not as efficient as for chlorosomes. Interestingly, our data suggest that excitation quenching partially proceeds from higher excitonic states competing with ultrafast exciton relaxation. Moreover, we obtained structure-related parameters such as reorganization energies and inhomogeneous broadening of the lowest excited state, providing experimental ground for theoretical studies aiming at designing plausible large-scale model for BChl c aggregates including disorder.
The peripheral light-harvesting antenna complex (LH2) of purple photosynthetic bacteria is an ideal testing ground for models of structure-function relationships due to its well-determined molecular structure and ultrafast energy deactivation. It has been the target for numerous studies in both theory and ultrafast spectroscopy; nevertheless, certain aspects of the convoluted relaxation network of LH2 lack a satisfactory explanation by conventional theories. For example, the initial carotenoid-to-bacteriochlorophyll energy transfer step necessary on visible light excitation was long considered to follow the Förster mechanism, even though transfer times as short as 40 femtoseconds (fs) have been observed. Such transfer times are hard to accommodate by Förster theory, as the moderate coupling strengths found in LH2 suggest much slower transfer within this framework. In this study, we investigate LH2 from Phaeospirillum (Ph.) molischianum in two types of transient absorption experiments-with narrowband pump and white-light probe resulting in 100 fs time resolution, and with degenerate broadband 10 fs pump and probe pulses. With regard to the split Qx band in this system, we show that vibronically mediated transfer explains both the ultrafast carotenoid-to-B850 transfer, and the almost complete lack of transfer to B800. These results are beyond Förster theory, which predicts an almost equal partition between the two channels.
- MeSH
- bakteriochlorofyly metabolismus MeSH
- časové faktory MeSH
- Fourierova analýza MeSH
- karotenoidy metabolismus MeSH
- lasery MeSH
- přenos energie * MeSH
- Proteobacteria metabolismus MeSH
- spektrofotometrie ultrafialová MeSH
- světlosběrné proteinové komplexy metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
Magnesium (Mg2+) is the ubiquitous metal ion present in chlorophyll and bacteriochlorophyll (BChl), involved in photosystems in photosynthetic organisms. In the present study we investigated targets of toxic copper binding to the photosynthetic apparatus of the anoxygenic purple bacterium Rhodospirillum rubrum. This was done by a combination of in vivo measurements of flash photolysis and fast fluorescence kinetics combined with the analysis of metal binding to pigments and pigment-protein complexes isolated from Cu-stressed cells by HPLC-ICPMS (ICP-sfMS). This work concludes that R. rubrum is highly sensitive to Cu2+, with a strong inhibition of the photosynthetic reaction centres (RCs) already at 2 μM Cu2+. The inhibition of growth and of RC activity was related to the formation of Cu-containing BChl degradation products that occurred much more in the RC than in LH1. These results suggest that the shift of metal centres in BChl from Mg2+ to Cu2+ can occur in vivo in the RCs of R. rubrum under environmentally realistic Cu2+ concentrations, leading to a strong inhibition of the function of these RCs.
RC-LH1-PufX complexes from a genetically modified strain of Rhodobacter sphaeroides that accumulates carotenoids with very long conjugation were studied by ultrafast transient absorption spectroscopy. The complexes predominantly bind the carotenoid diketospirilloxanthin, constituting about 75% of the total carotenoids, which has 13 conjugated C=C bonds, and the conjugation is further extended to two terminal keto groups. Excitation of diketospirilloxanthin in the RC-LH1-PufX complex demonstrates fully functional energy transfer from diketospirilloxanthin to BChl a in the LH1 antenna. As for other purple bacterial LH complexes having carotenoids with long conjugation, the main energy transfer route is via the S2-Qx pathway. However, in contrast to LH2 complexes binding diketospirilloxanthin, in RC-LH1-PufX we observe an additional, minor energy transfer pathway associated with the S1 state of diketospirilloxanthin. By comparing the spectral properties of the S1 state of diketospirilloxanthin in solution, in LH2, and in RC-LH1-PufX, we propose that the carotenoid-binding site in RC-LH1-PufX activates the ICT state of diketospirilloxanthin, resulting in the opening of a minor S1/ICT-mediated energy transfer channel.
- MeSH
- bakteriochlorofyly metabolismus MeSH
- fluorescenční spektrometrie MeSH
- karotenoidy metabolismus MeSH
- kinetika MeSH
- počítačové zpracování signálu MeSH
- přenos energie * MeSH
- Rhodobacter sphaeroides metabolismus MeSH
- světlosběrné proteinové komplexy metabolismus MeSH
- vysokoúčinná kapalinová chromatografie MeSH
- xanthofyly metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
Light-harvesting capacity was investigated in six species of aerobic anoxygenic phototrophic (AAP) bacteria using absorption spectroscopy, fluorescence emission spectroscopy, and pigment analyses. Aerobically grown AAP cells contained approx. 140-1800 photosynthetic reaction centers per cell, an order of magnitude less than purple non-sulfur bacteria grown semiaerobically. Three of the studied AAP species did not contain outer light-harvesting complexes, and the size of their reaction center core complexes (RC-LH1 core complexes) varied between 29 and 36 bacteriochlorophyll molecules. In AAP species containing accessory antennae, the size was frequently reduced, providing between 5 and 60 additional bacteriochlorophyll molecules. In Roseobacter litoralis, it was found that cells grown at a higher light intensity contained more reaction centers per cell, while the size of the light-harvesting complexes was reduced. The presented results document that AAP species have both the reduced number and size of light-harvesting complexes which is consistent with the auxiliary role of phototrophy in this bacterial group.
- MeSH
- aerobióza MeSH
- Alphaproteobacteria chemie metabolismus MeSH
- bakteriochlorofyly metabolismus MeSH
- fotosyntetická reakční centra (proteinové komplexy) chemie metabolismus MeSH
- fototrofní procesy MeSH
- Gammaproteobacteria chemie metabolismus MeSH
- světlosběrné proteinové komplexy chemie metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
A comparative two-photon excitation spectroscopic study of the exciton structure of the core antenna complex (LH1) and its subunit B820 was carried out. LH1 and its subunit B820 were isolated from cells of the carotenoid-less mutant G9 of Rhodospirillum rubrum. The measurements were performed by two-photon pump-probe spectroscopy. Samples were excited by 70 fs pulses at 1390 nm at a frequency of 1 kHz. Photoinduced absorption changes were recorded in the spectral range from 780 to 1020 nm for time delays of the probe pulse relative to the pump pulse in the - 1.5 to 11 ps range. All measurements were performed at room temperature. Two-photon excitation caused bleaching of exciton bands (k = 0, k = ± 1) of the circular bacteriochlorophyll aggregate of LH1. In the case of the B820 subunit, two-photon excitation did not cause absorption changes in this spectral range. It is proposed that in LH1 upper exciton branch states are mixed with charge-transfer (CT) states. In B820 such mixing is absent, precluding two-photon excitation in this spectral region. Usually, CT states are optically "dark", i.e., one photon-excitation forbidden. Thus, their investigation is rather complicated by conventional spectroscopic methods. Thus, our study provides a novel approach to investigate CT states and their interaction(s) with other excited states in photosynthetic light-harvesting complexes and other molecular aggregates.
We studied the distribution of anoxygenic phototrophs in 23 steppe lakes in the Transbaikal region (Russia), in Uzbekistan (Central Asia) and in the Crimean peninsula (Ukraine). The lakes varied in their mineral content and composition (salinities from 0.2 to 300 g L(-1) ). The Transbaikal lakes were alkaline (pH>9), with high amounts of soda. The Uzbek and Crimean lakes were more pH neutral, frequently with high amounts of sulfates. The presence of anoxygenic phototrophs was registered by infrared epifluorescence microscopy, infrared fluorometry and pigment analyses. In mostly shallow, fully oxic lakes, the anoxygenic phototrophs represented 7-65% of the total prokaryotes, with the maxima observed in Transbaikal soda lakes Gorbunka (32%), Khilganta (65%), Zanday (58%) and Zun-Kholvo (46%). Some of the lakes contained over 1 μg bacteriochlorophyll L(-1) . In contrast, only small amounts of anoxygenic phototrophs were present in highly mineralized lakes (>100 g total salts L(-1) ); Borzinskoe, Tsagan-Nur (Transbaikal), Staroe (Crimea) and in the residual part of the south-west Aral Sea (Uzbekistan). The oxic environment and the specific diurnal changes of bacteriochlorophyll concentration observed suggest that the phototrophic community was mostly composed of aerobic anoxygenic phototrophs. The high abundances and bacteriochlorophyll concentrations point to an important role of aerobic anoxygenic phototrophs in the habitats studied.
- MeSH
- Bacteria izolace a purifikace metabolismus MeSH
- bakteriochlorofyly analýza MeSH
- ekosystém MeSH
- fluorescenční mikroskopie MeSH
- fluorometrie MeSH
- fototrofní procesy MeSH
- mikrobiologie vody MeSH
- salinita MeSH
- vysokoúčinná kapalinová chromatografie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Geografické názvy
- Rusko MeSH
- Ukrajina MeSH
- Uzbekistán MeSH
163 s. : tab., grafy ; 22 cm
- MeSH
- bakteriochlorofyly terapeutické užití MeSH
- fotochemoterapie MeSH
- nádory terapie MeSH
- Rhodospirillum rubrum MeSH
- Publikační typ
- vysokoškolské kvalifikační práce MeSH
- Konspekt
- Patologie. Klinická medicína
- NLK Obory
- terapie
- bakteriologie
- onkologie
