The keto-carotenoid deinoxanthin, which occurs in the UV-resistant bacterium Deinococcus radiodurans, has been investigated by ultrafast time-resolved spectroscopy techniques. We have explored the excited-state properties of deinoxanthin in solution and bound to the S-layer Deinoxanthin Binding Complex (SDBC), a protein complex important for UV resistance and thermostability of the organism. Binding of deinoxanthin to SDBC shifts the absorption spectrum to longer wavelengths, but excited-state dynamics remain unaffected. The lifetime of the lowest excited state (S1) of isolated deinoxanthin in methanol is 2.1 ps. When bound to SDBC, the S1 lifetime is 2.4 ps, indicating essentially no alteration of the effective conjugation length upon binding. Moreover, our data show that the conformational disorder in both ground and excited states is the same for deinoxanthin in methanol and bound to SDBC. Our results thus suggest a rather loosely bound carotenoid in SDBC, making it very distinct from other carotenoid-binding proteins such as Orange Carotenoid Protein (OCP) or crustacyanin, both of which significantly restrain the carotenoid at the binding site. Three deinoxanthin analogs were found to bind the SDBC, suggesting a non-selective binding site of deinoxanthin in SDBC.

• MeSH
• bakteriální proteiny chemie   metabolismus   MeSH
• Deinococcus chemie   metabolismus   MeSH
• fotochemické procesy MeSH
• karotenoidy chemie   metabolismus   MeSH
• molekulární struktura MeSH
• vazebná místa MeSH
• Publikační typ
• časopisecké články MeSH

Photosynthetic eukaryotes whose cells harbor plastids originating from secondary endosymbiosis of a red alga include species of major ecological and economic importance. Since utilization of solar energy relies on the efficient light-harvesting, one of the critical factors for the success of the red lineage in a range of environments is to be found in the adaptability of the light-harvesting machinery, formed by the proteins of the light-harvesting complex (LHC) family. A number of species are known to employ mainly a unique class of LHC containing red-shifted chlorophyll a (Chl a) forms absorbing above 690 nm. This appears to be an adaptation to shaded habitats. Here we present a detailed investigation of excitation energy flow in the red-shifted light-harvesting antenna of eustigmatophyte Trachydiscus minutus using time-resolved fluorescence and ultrafast transient absorption measurements. The main carotenoid in the complex is violaxanthin, hence this LHC is labeled the red-violaxanthin-Chl a protein, rVCP. Both the carotenoid-to-Chl a energy transfer and excitation dynamics within the Chl a manifold were studied and compared to the related antenna complex, VCP, that lacks the red-Chl a. Two spectrally defined carotenoid pools were identified in the red antenna, contributing to energy transfer to Chl a, mostly via S2 and hot S1 states. Also, Chl a triplet quenching by carotenoids is documented. Two separate pools of red-shifted Chl a were resolved, one is likely formed by excitonically coupled Chl a molecules. The structural implications of these observations are discussed.

• MeSH
• chlorofyl a * MeSH
• Chlorophyta fyziologie   MeSH
• fluorescenční spektrometrie metody   MeSH
• Heterokontophyta fyziologie   MeSH
• plastidy MeSH
• přenos energie fyziologie   MeSH
• Rhodophyta fyziologie   MeSH
• světlosběrné proteinové komplexy chemie   MeSH
• xanthofyly MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

Chl synthase (ChlG) is an important enzyme of the Chl biosynthetic pathway catalyzing attachment of phytol/geranylgeraniol tail to the chlorophyllide molecule. Here we have investigated the Flag-tagged ChlG (f.ChlG) in a complex with two different high-light inducible proteins (Hlips) HliD and HliC. The f.ChlG-Hlips complex binds a Chl a and three different carotenoids, β-carotene, zeaxanthin and myxoxanthophyll. Application of ultrafast time-resolved absorption spectroscopy performed at room and cryogenic temperatures revealed excited-state dynamics of complex-bound pigments. After excitation of Chl a in the complex, excited Chl a is efficiently quenched by a nearby carotenoid molecule via energy transfer from the Chl a Qy state to the carotenoid S1 state. The kinetic analysis of the spectroscopic data revealed that quenching occurs with a time constant of ~2ps and its efficiency is temperature independent. Even though due to its long conjugation myxoxanthophyll appears to be energetically best suited for role of Chl a quencher, based on comparative analysis and spectroscopic data we propose that β-carotene bound to Hlips acts as the quencher rather than myxoxanthophyll and zeaxanthin, which are bound at the f.ChlG and Hlips interface. The S1 state lifetime of the quencher has been determined to be 13ps at room temperature and 21ps at 77K. These results demonstrate that Hlips act as a conserved functional module that prevents photodamage of protein complexes during photosystem assembly or Chl biosynthesis.

• MeSH
• bakteriální proteiny chemie   MeSH
• fotolýza MeSH
• karotenoidy farmakologie   MeSH
• ligasy tvořící vazby C-O chemie   MeSH
• sinice enzymologie   MeSH
• světlosběrné proteinové komplexy chemie   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Research Support, U.S. Gov't, Non-P.H.S. MeSH

Energy relaxation in light-harvesting complexes has been extensively studied by various ultrafast spectroscopic techniques, the fastest processes being in the sub-100-fs range. At the same time, much slower dynamics have been observed in individual complexes by single-molecule fluorescence spectroscopy (SMS). In this work, we use a pump-probe-type SMS technique to observe the ultrafast energy relaxation in single light-harvesting complexes LH2 of purple bacteria. After excitation at 800 nm, the measured relaxation time distribution of multiple complexes has a peak at 95 fs and is asymmetric, with a tail at slower relaxation times. When tuning the excitation wavelength, the distribution changes in both its shape and position. The observed behavior agrees with what is to be expected from the LH2 excited states structure. As we show by a Redfield theory calculation of the relaxation times, the distribution shape corresponds to the expected effect of Gaussian disorder of the pigment transition energies. By repeatedly measuring few individual complexes for minutes, we find that complexes sample the relaxation time distribution on a timescale of seconds. Furthermore, by comparing the distribution from a single long-lived complex with the whole ensemble, we demonstrate that, regarding the relaxation times, the ensemble can be considered ergodic. Our findings thus agree with the commonly used notion of an ensemble of identical LH2 complexes experiencing slow random fluctuations.

• MeSH
• bakteriochlorofyly chemie   účinky záření   MeSH
• čas MeSH
• fluorescenční spektrometrie metody   MeSH
• konfokální mikroskopie MeSH
• lasery MeSH
• neparametrická statistika MeSH
• normální rozdělení MeSH
• přenos energie * MeSH
• Rhodopseudomonas chemie   MeSH
• světlo MeSH
• světlosběrné proteinové komplexy chemie   účinky záření   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Research Support, U.S. Gov't, Non-P.H.S. MeSH
• srovnávací studie MeSH

The major light-harvesting complex of Amphidinium (A.) carterae, chlorophyll-a-chlorophyll-c 2-peridinin-protein complex (acpPC), was studied using ultrafast pump-probe spectroscopy at low temperature (60 K). An efficient peridinin-chlorophyll-a energy transfer was observed. The stimulated emission signal monitored in the near-infrared spectral region was stronger when redder part of peridinin pool was excited, indicating that these peridinins have the S1/ICT (intramolecular charge-transfer) state with significant charge-transfer character. This may lead to enhanced energy transfer efficiency from "red" peridinins to chlorophyll-a. Contrary to the water-soluble antenna of A. carterae, peridinin-chlorophyll-a protein, the energy transfer rates in acpPC were slower under low-temperature conditions. This fact underscores the influence of the protein environment on the excited-state dynamics of pigments and/or the specificity of organization of the two pigment-protein complexes.

• MeSH
• blízká infračervená spektroskopie * MeSH
• časové faktory MeSH
• chlorofyl metabolismus   MeSH
• Dinoflagellata metabolismus   MeSH
• elektrony MeSH
• karotenoidy metabolismus   MeSH
• kinetika MeSH
• nízká teplota * MeSH
• přenos energie MeSH
• světlosběrné proteinové komplexy metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

The ultrafast dynamic processes initiated by ioni¬zing radiation in water are discussed. At low photon energies, the primary processes are photoexcitation and photoionization. Both reaction channels ultimately lead to the formation of reactive species such as OH•radical or solvated electron. Ejection of low-lying electrons initiate further electron processes such as the Auger decay or the recently identified intermolecular Coulomb decay. All these processes contribute to radiation damage of biomolecules. Novel experimental and theoretical methods used for the study of primary events in radiation chemistry of water are described.

• Klíčová slova
• radiační chemie, Augerův rozpad, intermolekulární coulombovský rozpad, solvatovaný elektron, neadiabatická dynamika,
• MeSH
• voda MeSH

• MeSH
• biofyzika MeSH
• chromatin MeSH
• DNA MeSH
• genom MeSH
• kolorektální nádory diagnóza   MeSH
• metylace MeSH
• průtoková cytometrie využití   metody   MeSH
• Publikační typ
• kongresy MeSH
• sborníky MeSH

• Konspekt
• Biochemie. Molekulární biologie. Biofyzika
• NLK Obory
• biologie
• biochemie

• MeSH
• molekulární biologie MeSH
• spektrální analýza MeSH
• Publikační typ
• abstrakty MeSH

• Konspekt
• Biochemie. Molekulární biologie. Biofyzika
• NLK Obory
• biologie
• radiologie, nukleární medicína a zobrazovací metody

• MeSH
• chorobopisy - počítačové systémy MeSH
• management znalostí MeSH
• metody pro podporu rozhodování MeSH
• péče o pacienta MeSH
• počítačové zpracování obrazu MeSH
• počítačové zpracování signálu MeSH
• řízení zdravotnictví MeSH
• studium lékařství MeSH
• zdravotnické informační systémy MeSH
• Publikační typ
• sborníky MeSH

• Konspekt
• Lékařské vědy. Lékařství
• NLK Obory
• lékařská informatika
• NLK Publikační typ
• ročenky