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Robert E. Blankenship - One of the best experts on this subject based on the ideXlab platform.

  • SANS Investigation of the Photosynthetic Machinery of Chloroflexus aurantiacus
    Biophysical journal, 2010
    Co-Authors: Kuohsiang Tang, Jianzhong Wen, Yueyong Xin, Volker S. Urban, Robert E. Blankenship
    Abstract:

    Green photosynthetic bacteria harvest light and perform photosynthesis in low-light environments, and contain specialized antenna complexes to adapt to this condition. We performed small-angle neutron scattering (SANS) studies to obtain structural information about the photosynthetic apparatus, including the peripheral light-harvesting chlorosome complex, the integral membrane light-harvesting B808-866 complex, and the reaction center (RC) in the thermophilic green phototrophic bacterium Chloroflexus aurantiacus. Using contrast variation in SANS measurements, we found that the B808-866 complex is wrapped around the RC in Cfx. aurantiacus, and the overall size and conformation of the B808-866 complex of Cfx. aurantiacus is roughly comparable to the LH1 antenna complex of the purple bacteria. A similar size of the isolated B808-866 complex was suggested by dynamic light scattering measurements, and a smaller size of the RC of Cfx. aurantiacus compared to the RC of the purple bacteria was observed. Further, our SANS measurements indicate that the chlorosome is a lipid body with a rod-like shape, and that the self-assembly of bacteriochlorophylls, the major component of the chlorosome, is lipid-like. Finally, two populations of chlorosome particles are suggested in our SANS measurements.

  • Structural Analysis of Alternative Complex III in the Photosynthetic Electron Transfer Chain of Chloroflexus aurantiacus
    Biochemistry, 2010
    Co-Authors: Xinliu Gao, Yueyong Xin, Patrick D. Bell, Jianzhong Wen, Robert E. Blankenship
    Abstract:

    Bacterial electron transport pathways largely fall into two major categories: the light-driven photosynthetic electron transfer chain and the aerobic or anaerobic respiratory electron transfer chain. Despite the vast differences between photo- and oxidative phosphorylations, they both couple the chemical reactions between electron donors and electron accepters to the translocation of protons across the membrane, which then drives ATP formation and other energy-dependent processes (1). As a result, the common feature of all electron transport chains is the presence of a proton pump to create the transmembrane proton gradient. In respiratory electron transfer pathways, there may be as many as three types of proton pumping protein complexes reminiscent of mitochondria, depending on environmental factors (2). In contrast, the proton pump in all the photosynthetic electron transfer chains was until recently believed to involve a cytochrome bc1 or b6f complex, which resemble mitochondrial complex III in terms of overall structure and mechanism (3). In the species tree of bacteria based on 16S rRNA analysis (4), the phylum of filamentous anoxygenic phototrophs (FAPs) is not closely related to the other phyla that contain organisms that carry out chlorophyll-based photosynthesis; purple bacteria, cyanobacteria, heliobacteria, green sulfur bacteria and chloroacidobacteria. Instead, it exhibits a much deeper branching position to the other five bacterial phyla that contain phototrophic representatives (5, 6). Because of this distinctive feature, the study of FAPs may shed an interesting light on the evolutionary development of photosynthesis. The FAPs are a very diverse and unique phylum of bacteria including several genera: Chloroflexus (7), Oscillochloris (8), Chloronema (9), Heliothrix (10) and several Chloroflexus-like bacteria found in marine environment (11). Among them, Chloroflexus aurantiacus, a prominent microorganism of hot spring microbial mat communities, was the first described and is the most extensively studied representative of FAPs in terms of its photosynthetic and other metabolic pathways. The photosynthetic apparatus of Chloroflexus aurantiacus exhibits an interesting combination of characteristics found in very different and diverse groups of phototrophic prokaryotes. They have a type II photoreaction center and integral membrane antenna complex reminiscent of purple bacteria (12, 13). In addition, they have a peripheral chlorosome antenna complex (14) and a chlorophyll biosynthesis pathway that are both similar to those found in green sulfur bacteria (15, 16). Chloroflexus aurantiacus also contains a unique autotrophic carbon fixation pathway different from that found in any other phototrophs, the 3-hydroxypropinate cycle (17, 18). Therefore, the phylogenetic characterization and the versatile photosynthetic apparatus of Chloroflexus aurantiacus suggest that it occupies an important place in the origin and evolution of photosynthesis (19). An intriguing characteristic of Chloroflexus aurantiacus is its extraordinary electron transfer pathway. For all types of photosynthetic organisms, following the initial process where the light energy transforms into chemical energy, the electrons pass through a series of electron carriers and ultimately either return to the electron donor side of the photosystem via a cyclic electron transfer pathway, or reduce a terminal electron acceptor in a non-cyclic electron transfer process (1). The overall pattern of electron transfer depends critically on the type of the organism, the environment it occupies, whether aerobic or anaerobic metabolism takes place and what type of terminal oxidants and reductants are present. While the electron transfer pathways appear to be quite different in various groups of phototrophs, one component was until recently believed to be a constant constituent in all photosynthetic system: the cytochrome bc1 or b6f complex, which transfers electrons from quinol to soluble cytochrome c or plastocyanin and at the same time translocates protons across the membrane, creating a transmembrane proton motive force (20, 21). However, Chloroflexus aurantiacus, like other members of the FAP phylum, does not exhibit either biochemical or genomic evidence for the existence of a related cytochrome bc1 or b6f complex. The lack of a cytochrome bc1 or b6f complex suggests that this group of organisms contains an unusual photosynthetic electron transfer pathway. A multi-subunit protein complex containing c-type cytochromes but no characteristic features of a cytochrome bc1 complex was isolated from C. aurantiacus by Yanyushin (22). A similar complex from Rhodothermus marinus is now named alternative complex III (ACIII) (23, 24). These two complexes have been proposed to be the functional substitute of the cytochrome bc1 complex based on gene analysis of sequenced genomes of various species (25) and an enzymatic study of ACIII from R. marinus (23). Recent enzyme kinetic analysis showing that ACIII performs the function of a quinol:auracyanin oxidoreductase strongly supports the hypothesis that ACIII fulfills the functional role of cytochrome bc1 complex in the photosynthetic electron transfer chain in Chloroflexus aurantiacus (26). Figure 1 shows the proposed cyclic electron transfer pathway in Chloroflexus aurantiacus. Figure 1 The proposed photosynthetic cyclic electron transfer pathway in Chloroflexus aurantiacus. Based on the genome arrangement of ACIII genes and early fundamental structural studies, the organization of ACIII was revealed to be entirely different from that of cytochrome bc1 or b6f complexes. However, a challenging question emerges - how does ACIII, a complex with structure vastly different from the cytochrome bc complex, carry out the same function in the electron transfer pathway in photosynthesis? A complete picture of the structure and role of ACIII complex is still missing. The key to elucidating this system is therefore believed to reside in understanding the ACIII complex in terms of its substructure and how this relates to its function in photosynthesis and respiration. In this work, a schematic structural model of the photosynthetic ACIII complex is proposed based on chemical cross-linking of subunits in tandem with MALDI-TOF mass spectrometry. The size and type of each subunit was determined by gel electrophoresis including one and two dimensional SDS-PAGE and native PAGE. The type and number of cofactors existing in the ACIII complex was investigated using metal analysis, HPLC combined with ESI-MS and potentiometric titrations.

  • Enzymatic activity of the alternative complex III as a menaquinol:auracyanin oxidoreductase in the electron transfer chain of Chloroflexus aurantiacus.
    FEBS letters, 2009
    Co-Authors: Xinliu Gao, Yueyong Xin, Robert E. Blankenship
    Abstract:

    The surprising lack of the cytochrome bc1 complex in the filamentous anoxygenic phototrophic bacterium Chloroflexus aurantiacus suggests that a functional replacement exists to link the cyclic electron transfer chain. Earlier work identified the alternative complex III (ACIII) as a substitute of cytochrome bc1 complex. Herein, the enzymatic activity of ACIII is studied. The results strongly support the view that the ACIII functions as menaquinol:auracyanin oxidoreductase in the C. aurantiacus electron transfer chain. Among all the substrates tested, auracyanin is the most efficient electron acceptor of ACIII, suggesting that ACIII directly transfers the electron to auracyanin instead of cytochrome c-554. The lack of sensitivity to common inhibitors of the cytochrome bc1 complex indicates a different catalytic mechanism for the ACIII complex.

  • Structure of Chlorosomes from the Green Filamentous Bacterium Chloroflexus aurantiacus
    Journal of bacteriology, 2009
    Co-Authors: Jakub Psencik, Robert E. Blankenship, Teemu P Ikonen, Pasi Laurinmaki, Ritva Serimaa, Aaron M. Collins, Lassi Liljeroos, Mika Torkkeli, Hermanus M. Ansink, Roman Tuma
    Abstract:

    The green filamentous bacterium Chloroflexus aurantiacus employs chlorosomes as photosynthetic antennae. Chlorosomes contain bacteriochlorophyll aggregates and are attached to the inner side of a plasma membrane via a protein baseplate. The structure of chlorosomes from C. aurantiacus was investigated by using a combination of cryo-electron microscopy and X-ray diffraction and compared with that of Chlorobi species. Cryo-electron tomography revealed thin chlorosomes for which a distinct crystalline baseplate lattice was visualized in high-resolution projections. The baseplate is present only on one side of the chlorosome, and the lattice dimensions suggest that a dimer of the CsmA protein is the building block. The bacteriochlorophyll aggregates inside the chlorosome are arranged in lamellae, but the spacing is much greater than that in Chlorobi species. A comparison of chlorosomes from different species suggested that the lamellar spacing is proportional to the chain length of the esterifying alcohols. C. aurantiacus chlorosomes accumulate larger quantities of carotenoids under high-light conditions, presumably to provide photoprotection. The wider lamellae allow accommodation of the additional carotenoids and lead to increased disorder within the lamellae.

  • Role of the AcsF Protein in Chloroflexus aurantiacus
    Journal of bacteriology, 2009
    Co-Authors: Kuohsiang Tang, Jianzhong Wen, Robert E. Blankenship
    Abstract:

    The green phototrophic bacteria contain a unique complement of chlorophyll pigments, which self-assemble efficiently into antenna structures known as chlorosomes with little involvement of protein. The few proteins found in chlorosomes have previously been thought to have a primarily structural function. The biosynthetic pathway of the chlorosome pigments, bacteriochlorophylls c, d, and e, is not well understood. In this report, we used spectroscopic, proteomic, and gene expression approaches to investigate the chlorosome proteins of the green filamentous anoxygenic phototrophic bacterium Chloroflexus aurantiacus. Surprisingly, Mg-protoporphyrin IX monomethyl ester (oxidative) cyclase, AcsF, was identified under anaerobic growth conditions. The AcsF protein was found in the isolated chlorosome fractions, and the proteomics analysis suggested that significant portions of the AcsF proteins are not accessible to protease digestion. Additionally, quantitative real-time PCR studies showed that the transcript level of the acsF gene is not lower in anaerobic growth than in semiaerobic growth. Since the proposed enzymatic activity of AcsF requires molecular oxygen, our studies suggest that the roles of AcsF in C. aurantiacus need to be investigated further.

Reiner Feick - One of the best experts on this subject based on the ideXlab platform.

  • Structure and Protein Binding Interactions of the Primary Donor of the Chloroflexus aurantiacus Reaction Center
    Biochemistry, 1996
    Co-Authors: Anabella Ivancich, Reiner Feick, And Angelika Ertlmaier, Tony A. Mattioli
    Abstract:

    Soret resonance, QX resonance, and QY near-infrared Fourier transform (FT) (pre)resonance Raman spectroscopies were used to determine pigment-protein interactions of specific bacteriochlorin molecules in the reaction center from Chloroflexus aurantiacus. FT Raman spectroscopy, using 1064 nm excitation, was used to selectively obtain preresonance and resonance vibrational Raman spectra of the primary donor (P) of reaction centers (RCs) from Chloroflexus aurantiacus in the Po and P.+ states, respectively. The FT Raman spectrum of RCs in their neutral P (Po) state exhibits bands at 1605, 1632, 1648, and 1696 cm-1 which are attributable to P in its resting neutral state. Specifically, the latter three Raman bands can be assigned to the conjugated C2 acetyl and C9 keto carbonyl groups of the bacteriochlorophyll (BChl) molecules constituting P. The observation of at least three such bands is indicative of a non-monomeric nature of P, consistent with the proposal that it is a dimer of BChl molecules. The 1632 cm-1 band is consistent only with a hydrogen bonded BChl acetyl carbonyl, while the 1648 cm-1 band is assigned to a non-hydrogen bonded acetyl carbonyl. The 1696 cm-1 band is consistent only with a non-hydrogen bonded keto carbonyl group; from the unusually high intensity of this latter band compared to the others, we propose that the 1696 cm-1 band contains contributions from two keto carbonyl groups, both free of hydrogen bonds. From published protein sequence alignments of the L and M subunits of Rhodobacter (Rb.) sphaeroides and Chloroflexus aurantiacus we assign the 1632 cm-1 band as arising from the C2 acetyl carbonyl of the analogous PM constituent of P, which is hydrogen bonded to tyrosine M187 in the Chloroflexus RC, and propose a pigment-protein structural model for the primary donor of Chloroflexus aurantiacus. The FT Raman spectrum of RCs in the P degrees+ state indicates that one component of the 1696 cm-1 band has upshifted 21 cm-1 to 1717 cm-1. Compared to Rb. sphaeroides which showed a 26 cm-1 upshift for the corresponding band, the 21 cm-1 upshift indicates that the + charge is more delocalized over the P.+ species of Chloroflexus; we estimate that ca. 65% of the + charge is localized on one of the two BChl molecules of the Chloroflexus primary donor as compared to ca. 80% for Rb. sphaeroides. The consequences of the proposed structure of the Chloroflexus primary donor in terms of its Po/P.+ redox midpoint potential are discussed.

  • Structure and Protein Binding Interactions of the Primary Donor of Chloroflexus aurantiacus
    Spectroscopy of Biological Molecules, 1995
    Co-Authors: Anabella Ivancich, Reiner Feick, And Angelika Ertlmaier, Tony A. Mattioli
    Abstract:

    Chloroflexus aurantiacus is a thermophilic, filamentous green gliding photosynthetic bacterium from the family of the Chloroflexaceae. C. auranticus is found in the earliest branches of the bacterial phylogenetic tree and thus has prompted several authors to propose a photosynthetic common ancestor of all Bacteria (see Nitschke et al., 1995).

  • The primary structure of two chlorosome proteins from Chloroflexus aurantiacus.
    FEBS letters, 1994
    Co-Authors: Georg Niedermeier, Friedrich Lottspeich, Judith A. Shiozawa, Reiner Feick
    Abstract:

    Abstract The complete nucleotide sequence of two chlorosome proteins with apparent molecular weights of M r 18,000 and M r 11,000 from Chloroflexus aurantiacus have been determined. The two polypeptides were 145 and 97 amino acids long and possessed true molecular masses of 15,545 and 10,820 Da, respectively. Protein chemical sequencing was done in parallel to confirm the primary structure deduced from nucleotide sequencing. By Northern blot analysis of RNA isolated from phototrophically grown cells a transcript of 0.95 kb was detected which is the expected length for a mRNA encoding both genes.

  • High quantum yield of charge separation in reaction centers of Chloroflexus aurantiacus
    Biochimica et Biophysica Acta (BBA) - Bioenergetics, 1991
    Co-Authors: Martin Volk, Reiner Feick, G. Scheidel, A. Ogrodnik, Maria-elisabeth Michel-beyerle
    Abstract:

    The relative quantum yield of charge separation in photosynthetic reaction centers of Chloroflexus aurantiacus and Rhodobacter sphaeroides was measured on the nanosecond timescale. Thereby the quantum yield becomes independent of a potential loss of both quinones during reaction center isolation. Based on the quantum yield of 1.02±0.04 for reaction centers of Rhodobacter sphaeroides at room temperature (Wraight, C.A. and Clayton, R.K. (1973) Biochim. Biophys. Acta 333, 246–260), the quantum yield of initial charge separation in reaction centers of Chloroflexus aurantiacus at 280 K was determined to be 1.06 ± 0.11.

Wolfgang Eisenreich - One of the best experts on this subject based on the ideXlab platform.

  • a bicyclic autotrophic co2 fixation pathway in Chloroflexus aurantiacus
    Journal of Biological Chemistry, 2002
    Co-Authors: Sylvia Herter, Georg Fuchs, Adelbert Bacher, Wolfgang Eisenreich
    Abstract:

    Phototrophic CO(2) assimilation by the primitive, green eubacterium Chloroflexus aurantiacus has been shown earlier to proceed in a cyclic mode via 3-hydroxypropionate, propionyl-CoA, succinyl-CoA, and malyl-CoA. The metabolic cycle could be closed by cleavage of malyl-CoA affording glyoxylate (the primary CO(2) fixation product) with regeneration of acetyl-CoA serving as the starter unit of the cycle. The pathway of glyoxylate assimilation to form gluconeogenic precursors has not been elucidated to date. We could now show that the incubation of cell extract with a mixture of glyoxylate and [1,2,3-(13)C(3)]propionyl-CoA afforded erythro-beta-[1,2,2'-(13)C(3)]methylmalate and [1,2,2'-(13)C(3)]citramalate. Similar experiments using a partially purified protein fraction afforded erythro-beta-[1,2,2'-(13)C(3)]methylmalyl-CoA and [1,2,2'-(13)C(3)]mesaconyl-CoA. Cell extracts of C. aurantiacus were also shown to catalyze the conversion of citramalate into pyruvate and acetyl-CoA in a succinyl-CoA-dependent reaction. The data suggest that glyoxylate obtained by the cleavage of malyl-CoA can be utilized by condensation with propionyl-CoA affording erythro-beta-methylmalyl-CoA, which is converted to acetyl-CoA and pyruvate. This reaction sequence regenerates acetyl-CoA, which serves as the precursor of propionyl-CoA in the 3-hydroxypropionate cycle. Autotrophic CO(2) fixation proceeds by combination of the 3-hydroxypropionate cycle with the methylmalyl-CoA cycle. The net product of that bicyclic autotrophic CO(2) fixation pathway is pyruvate serving as an universal building block for anabolic reactions.

  • biosynthesis of the diterpene verrucosan 2beta ol in the phototrophic eubacterium Chloroflexus aurantiacus a retrobiosynthetic nmr study
    Journal of Biological Chemistry, 1998
    Co-Authors: Christoph Rieder, Georg Fuchs, Adelbert Bacher, Gerhard Straus, Duilio Arigoni, Wolfgang Eisenreich
    Abstract:

    Abstract The biosynthesis of verrucosan-2β-ol in the green phototrophic eubacterium Chloroflexus aurantiacus was investigated by in vivo incorporation of singly or doubly13C-labeled acetate. The 13C labeling of the isolated diterpene was analyzed by one- and two-dimensional NMR spectroscopy. The 13C-labeling patterns of verrucosan-2β-ol were compared with the labeling patterns of intermediary metabolites (acetyl-CoA, pyruvate, and glyceraldehyde 3-phosphate) which were deduced from amino acids and nucleosides by retrobiosynthetic analysis. The results show that verrucosan-2β-ol is synthesized via mevalonate and not via the deoxyxylulose pathway, which was discovered recently in some eubacteria, algae, and plants. A scheme for the formation of the unusual tetracyclic ring system is offered. The cyclization process is initiated by the solvolysis of pyrophosphate from geranyllinaloyl pyrophosphate and the mechanism involves a Wagner-Meerwein rearrangement, a 1,5-hydride shift, and a cyclopropylcarbinyl to cyclopropylcarbinyl rearrangement.

Alfred R Holzwarth - One of the best experts on this subject based on the ideXlab platform.

  • near infrared resonance raman spectra of Chloroflexus aurantiacus photosynthetic reaction centers
    Biochemistry, 1995
    Co-Authors: Nerine J Cherepy, Alfred R Holzwarth, Richard A Mathies
    Abstract:

    Resonance Raman spectra of the photosynthetic reaction center isolated from the green bacterium Chloroflexus aurantiacus have been obtained with excitation in the near-infrared absorption bands of the special pair (P) and the accessory bacteriochlorophyll (B) using shifted-excitation Raman difference spectroscopy (SERDS). These spectra are compared with the previously reported Raman spectra of P and B in reaction centers from the purple bacterium Rhodobacter sphaeroides. The spectra of P and B from the two species are nearly identical. Common and distinctive attributes of these spectra include enhanced low-frequency (30-200 cm-1) modes in P and the absence of strong Raman activity in modes higher than 1200 cm-1 in both P and B. Also, the absolute scattering cross sections with excitation in the P band are unusually weak in both reaction centers, indicating that their excited states are rapidly vibronically dephased. The striking similarities between the P and B spectra in reaction centers from two very different bacterial species suggest that the common nuclear and electronic dynamics identified here are characteristic of photosynthetic reaction centers.

  • Charge separation kinetics in isolated photosynthetic reaction centers of Chloroflexus aurantiacus (with QA reduced) at low temperatures
    Chemical Physics Letters, 1992
    Co-Authors: Gerd Schweitzer, M. Hucke, Kai Griebenow, Marc Muller, Alfred R Holzwarth
    Abstract:

    Abstract The picosecond fluorescence kinetics of closed (quinone acceptor QA reduced) reaction centers isolated from the phototrophic bacterium Chloroflexus aurantiacus shows time constants of ≈ 20 and ≈ 300 ps (amplitude ratio ≈ 1:1), which are nearly independent of temperature (7 to 80 K). Assuming a three-state kinetic model, we tested various assignments of the kinetics to the electron transfer processes. Only two of these assignments seem to be physically reasonable. One of these includes a fast reversible electron transfer between P* and HM, the pheophytin(s) in the M branch of the reaction center which up to now has been considered virtually inactive in electron transfer. The other possible model involves the formation of a monomeric bacteriochlorophyll anion.

Walter S. Struve - One of the best experts on this subject based on the ideXlab platform.

  • excitation delocalization in the bacteriochlorophyll c antenna of the green bacterium Chloroflexus aurantiacus as revealed by ultrafast pump probe spectroscopy
    FEBS Letters, 1998
    Co-Authors: Sergei Savikhin, Robert E. Blankenship, Vladimir I. Novoderezhkin, Alexandra Taisova, Walter S. Struve, Daniel R Buck, Zoya G. Fetisova
    Abstract:

    Room temperature absorption difference spectra were measured on the femtosecond through picosecond time scales for chlorosomes isolated from the green bacterium Chloroflexus aurantiacus. Anomalously high values of photoinduced absorption changes were revealed in the BChl c Qy transition band. Photoinduced absorption changes at the bleaching peak in the BChl c band were found to be 7–8 times greater than those at the bleaching peak in the BChl a band of the chlorosome. This appears to be the first direct experimental proof of excitation delocalization over many BChl c antenna molecules in the chlorosome.

  • energy transfers in the b808 866 antenna from the green bacterium Chloroflexus aurantiacus
    Biophysical Journal, 1998
    Co-Authors: Vladimir I. Novoderezhkin, Robert E. Blankenship, Alexandra Taisova, Zoya G. Fetisova, Sergei Savikhin, Daniel R Buck, Walter S. Struve
    Abstract:

    Energy transfers within the B808-866 BChl a antenna in chlorosome-membrane complexes from the green photosynthetic bacterium Chloroflexus aurantiacus were studied in two-color pump-probe experiments at room temperature. The steady-state spectroscopy and protein sequence of the B808-866 complex are reminiscent of well-studied LH2 antennas from purple bacteria. B808-->B866 energy transfers occur with approximately 2 ps kinetics; this is slower by a factor of approximately 2 than B800-->B850 energy transfers in LH2 complexes from Rhodopseudomonas acidophila or Rhodobacter sphaeroides. Anisotropy studies show no evidence for intra-B808 energy transfers before the B808-->B866 step; intra-B866 processes are reflected in 350-550 fs anisotropy decays. Two-color anisotropies under 808 nm excitation suggest the presence of a B808-->B866 channel arising either from direct laser excitation of upper B866 exciton components that overlap the B808 absorption band or from excitation of B866 vibronic bands in nontotally symmetric modes.

  • ultrafast energy transfer in chlorosomes from the green photosynthetic bacterium Chloroflexus aurantiacus
    The Journal of Physical Chemistry, 1996
    Co-Authors: Sergei Savikhin, Robert E. Blankenship, Yinwen Zhu, Walter S. Struve
    Abstract:

    Energy transfers between the bacteriochlorophyll c and a antennae in light-harvesting chlorosomes from the green bacterium Chloroflexus aurantiacus have been studied in two-color pump-probe experiments with improved sensitivity and wavelength versatility. The BChl c {yields} BChl a energy transfers are well simulated with biexponential kinetics, with lifetimes of 2-3 and 11 ps. They do not exhibit an appreciable subpicosecond component. In the context of a kinetic model for chlorosomes, these lifetimes suggest that both internal BChl c processes and the BChl c {yields} BChl a energy-transfer step contribute materially to the empirical rod-to-baseplate energy-transfer kinetics. 11 refs., 2 figs., 1 tab.

  • Intraband energy transfers in the BChl c antenna of chlorosomes from the green photosynthetic bacterium Chloroflexus aurantiacus
    The Journal of Physical Chemistry, 1996
    Co-Authors: Sergei Savikhin, Robert E. Blankenship, Yinwen Zhu, Walter S. Struve
    Abstract:

    Two-color absorption difference profiles for the bacteriochlorophyll (BChl) c antenna of chlorosomes from Chloroflexus aurantiacus at 19 K show photobleaching/stimulated emission rise features with ∼300 fs kinetics when the probe wavelength is ∼30 nm to the red of the excitation wavelength. Similar rise features do not appear at 300 K, or in uphill two-color experiments at 19 K, or when the pump and probe wavelengths are separated by ≪30 nm. This appears to be the first direct observation of downhill electronic energy transfers within light-harvesting BChl c oligomers in intact chlorosomes.

  • femtosecond spectroscopy of chlorosome antennas from the green photosynthetic bacterium Chloroflexus aurantiacus
    The Journal of Physical Chemistry, 1994
    Co-Authors: Sergei Savikhin, Robert E. Blankenship, Su Lin, Yinwen Zhu, Walter S. Struve
    Abstract:

    The antenna kinetics of bacteriochlorophyll (BChl) c- and a-containing chromosomes from the thermophilic filamentous green photosynthetic bacterium Chloroflexus aurantiacus were investigated using two independent pump-probe techniques with subpicosecond resolution. Isotropic one- and two-color absorption difference experiments using probe wavelengths between 710 and 770 nm reveal BChl c photobleaching (PB) and stimulated emission (SE) decay kinetics with major lifetime components of 50-100 fs, 1-2 ps, and 7-10 ps. Two-color PB.SE profiles pumped at 770 nm and probed at 800 nm (where BChl a pigments absorb) exhibit no detectable rise time. However, two-color experiments using 790 and 820 nm pump and probe wavelengths, respectively, yield PB/SE rise components of 100 fs, 2 ps, and 10 ps. Upon excitation at 720 nm, the BCHl c PB/SE spectrum observed using a broad-band probe continuum displays surprisingly little spectral evolution during the first 2 ps. 65 refs., 13 figs., 3 tabs.