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1.
Umetsu Mitsuo Wang Zheng-Yu Zhang Jun Ishii Takasada Uehara Kaku Inoko Yoji Kobayashi Masayuki Nozawa Tsunenori 《Photosynthesis research》1999,60(2-3):229-239
The change of absorption spectra has been measured during the drying process of (31 R)bacteriochlorophyll (BChl) c from diethyl ether, dichloromethane (CH2Cl2) and carbon tetrachloride (CCl4) solutions. Absorption maxima of the Qy(0–0) transition of BChl c appear at 659 nm in diethyl ether, 680 nm in CH2Cl2 and 710 nm in CCl4. All these peaks are red-shifted to about 740 nm with formation of solid high aggregates when the solutions are completely dried. Fourier transform infrared spectra of the three solid aggregates are almost identical. However, magnetic circular dichroism and circular dichroism spectra are different and can be explained in terms of variations in stacking size of the aggregates and molecular arrangement of BChl c. Small-angle X-ray diffraction has been observed only for the aggregates treated with CH2Cl2, and the same sample gave rise to highly resolved cross polarization/magic angle spinning 13C nuclear magnetic resonance spectrum. The results suggest that molecular ordering of the solid-state BChl c aggregates is highly dependent on the formation process which is largely determined by the solvent used. 相似文献
2.
Phototransformation Pt to Pfr was investigated with 124-kDa phytochrome from etiolated oat seedlings ( Avena sativa L. cv. Pirol) using circular dichroism spectroscopy at -110°C to +30°C. Using absorption spectra of the intermediates formed at the respective temperatures, circular dichroism spectra (300–800 nm) of pure intermediates were calculated.
The sign of the circular dichroic absorption bands changed upon formation of lumi-R, the primary photoproduct of Pr . This would be compatible with a Z→E isomerization taking place at this reaction step. The subsequent intermediates (meta-Ra and meta-Rc ) as well as Pfr showed only small circular dichroism. Their absorption spectra were drastically shifted, but had similar spectral shapes. The results are discussed in terms of conformational changes of the phytochrome chromophore presumably taking place at the early steps of phototransformation Pr to Pfr . 相似文献
The sign of the circular dichroic absorption bands changed upon formation of lumi-R, the primary photoproduct of P
3.
《BBA》1985,809(2):199-203
Absorption, fluorescence emission and fluorescence excitation spectra of membranes of the recently discovered photosynthetic bacterium Heliobacterium chlorum (Gest, H. and Favinger, J.L. (1983) Arch. Microbiol. 136, 11–16) showed that at 4 K at least three spectroscopically different forms of bacteriochlorophyll g (BChl g 778, BChl g 793 and BChl g 808) can be discerned in the antenna system. Efficient energy transfer occurs from the short-wave-absorbing bacteriochlorophylls to BChl g 808. Energy transfer to bacteriochlorophyll, albeit with lower efficiency (70%), also occurred from the main carotenoid, neurosporene, and from a pigment absorbing at 670 nm. The complex structure of the antenna system is also reflected by fluorescence polarization and linear and circular dichroism spectra. Significant circular dichroism was only observed for BChl g 793, and different orientations were observed for the various Qy transition dipoles, the one of BChl g 808 making a smaller angle with the plane of the membrane than those of the other bacteriochlorophylls. 相似文献
4.
Stephan C. M. Otte Jos C. van der Heiden Norbert Pfennig Jan Amesz 《Photosynthesis research》1991,28(2):77-87
Energy transfer and pigment arrangement in intact cells of the green sulfur bacteria Prosthecochloris aestuarii, Chlorobium vibrioforme and chlorobium phaeovibrioides, containing bacteriochlorophyll (BChl) c, d or e as main light harvesting pigment, respectively, were studied by means of absorption, fluorescence, circular dichroism and linear dichroism spectroscopy at low temperature. The results indicate a very similar composition of the antenna in the three species and a very similar structure of main light harvesting components, the chlorosome and the membrane-bound BChl a protein. In all three species the Qy transition dipoles of BChl c, d or e are oriented approximately parallel to the long axis of the chlorosome. Absorption and fluorescence excitation spectra demonstrate the presence of at least two BChl c-e pools in the chlorosomes of all three species, long-wavelength absorbing BChls being closest to the membrane. In C. phaeovibrioides, energy from BChl e is transferred with an efficiency of 25% to the chlorosomal BChl a at 6 K, whereas the efficiency of transfer from BChl e to the BChl a protein is 10%. These numbers are compatible with the hypothesis that the chlorosomal BChl a is an intermediary in the energy transfer from the chlorosome to the membrane.Abbreviations BChl
bacteriochlorophyll
- Chl
chlorophyll
- CD
circular dichroism
- LD
linear dichroism 相似文献
5.
Mamoru Mimuro Yoshinobu Nishimura Iwao Yamazaki Masayuki Kobayashi Zheng Yu Wang Tsunenori Nozawa Keizo Shimada Katsumi Matsuura 《Photosynthesis research》1996,48(1-2):263-270
The effect of 1-hexanol on spectral properties and the processes of energy transfer of the green gliding photosynthetic bacterium Chloroflexus aurantiacus was investigated with reference to the baseplate region. On addition of 1-hexanol to a cell suspension in a concentration of one-fourth saturation, a specific change in the baseplate region was induced: that is, a bleach of the 793-nm component, and an increase in absorption of the 813-nm component. This result was also confirmed by fluorescence spectra of whole cells and isolated chlorosomes. The processes of energy transfer were affected in the overall transfer efficiency but not kinetically, indicating that 1-hexanol suppressed the flux of energy flow from the baseplate to the B806-866 complexes in the cytoplasmic membranes. The fluorescence excitation spectrum suggests a specific site of interaction between bacteriochlorophyll (BChl) c with a maximum at 771 nm in the rod elements and BChl a with a maximum at 793 nm in the baseplate, which is a funnel for a fast transfer of energy to the B806-866 complexes in the membranes. The absorption spectrum of chlorosomes was resolved to components consistently on the basis, including circular dichroism and magnetic circular dichroism spectra; besides two major BChl c forms, bands corresponding to tetramer, dimer, and monomer were also discernible, which are supposed to be intermediary components for a higher order structure. A tentative model for the antenna system of C. aurantiacus is proposed.Abbreviations A670
a component whose absorption maximum is located at 670 nm
- (B)Chl
(bacterio)chlorophyll
- CD
circular dichroism
- F675
a component whose emission maximum is located at 675 nm
- FMO protein
Fenna-Mathews-Olson protein
- LD
linear dichroism
- LH
light-harvesting
- McD
magnetic circular dichroism
- PS
photosystem
- RC
reaction center 相似文献
6.
We have used measurements of fluorescence and circular dichroism (CD) to compare chlorosome-membrane preparations derived from the green filamentous bacterium Chloroflexus aurantiacus grown in continuous culture at two different light-intensities. The cells grown under low light (6 mol m–2 s–1) had a higher ratio of bacteriochlorophyll (BChl) c to BChl a than cells grown at a tenfold higher light intensity; the high-light-grown cells had much more carotenoid per bacteriochlorophyll.The anisotropy of the QY band of BChl c was calculated from steady-state fluorescence excitation and emission spectra with polarized light. The results showed that the BChl c in the chlorosomes derived from cells grown under high light has a higher structural order than BChl c in chlorosomes from low-light-grown cells. In the central part of the BChl c fluorescence emission band, the average angles between the transition dipole moments for BChl c molecules and the symmetry axis of the chlorosome rod element were estimated as 25° and 17° in chlorosomes obtained from the low- and high-light-grown cells, respectively.This difference in BChl organization was confirmed by the decay associated spectra of the two samples obtained using picosecond single-photon-counting experiments and global analysis of the fluorescence decays. The shortest decay component obtained, which probably represents energy-transfer from the chlorosome bacteriochlorophylls to the BChl a in the baseplate, was 15 ps in the chlorosomes from high-light-grown cell but only 7 ps in the preparation from low-light grown cells. The CD spectra of the two preparations were very different: chlorosomes from low-light-grown cells had a type II spectrum, while those from high-light-grown cells was of type I (Griebenow et al. (1991) Biochim Biophys Acta 1058: 194–202). The different shapes of the CD spectra confirm the existence of a qualitatively different organization of the BChl c in the two types of chlorosome.Abbreviations BChl
bacteriochlorophyll
- CD
circular dichroism
- DAS
decay associated spectrum
- PMSF
phenylmethylsulfonyl fluoride 相似文献
7.
Frese Raoul Oberheide Uwe van Stokkum Ivo van Grondelle Rienk Foidl Markus Oelze Jürgen van Amerongen Herbert 《Photosynthesis research》1997,54(2):115-126
The organization of bacteriochlorophyll c (BChl c) molecules was studied in normal and carotenoid-deficient chlorosomes isolated from the green phototrophic bacterium Chloroflexus aurantiacus. Carotenoid-deficient chlorosomes were obtained from cells grown in the presence of 60 µg of 2-hydroxybiphenyl per ml. At this concentration, BChl c synthesis was not affected while the formation of the 5.7 kDa chlorosome polypeptide was inhibited by about 50% (M. Foidl et al., submitted). Absorption, linear dichroism and circular dichroism spectroscopy showed that the organization of BChl c molecules with respect to each other as well as to the long axis of the chlorosomes was similar for both types of chlorosomes. Therefore, it is concluded that the organization of BChl c molecules is largely independent on the presence of the bulk of carotenoids as well as of at least half of the normal amount of the 5.7 kDa polypeptide. The Stark spectra of the chlorosomes, as characterized by a large difference polarizability for the ground- and excited states of the interacting BChl c molecules, were much more intense than those of individual pigments. It is proposed that this is caused by the strong overlap of BChl c molecules in the chlorosomes. In contrast to individual chlorophylls, BChl c in chlorosomes did not give rise to a significant difference permanent dipole moment for the ground- and excited states. This observation favors models for the BChl c organization which invoke the anti-parallel stacking of linear BChl c aggregates above those models in which linear BChl c aggregates are stacked in a parallel fashion. The difference between the Stark spectrum of carotenoid-deficient and WT chlorosomes indicates that the carotenoids are in the vicinity of the BChls. 相似文献
8.
Naturally occurring bacteriochlorophyll(BChl)s-c, -d, and -e from green sulfur photosynthetic bacteria were self-assembled in an aqueous solution in the presence of octadecyltriethoxysilane and tetraethoxysilane, followed by polycondensation of the alkoxysilanes by incubation for 50 h at 25 degrees C. The resulting BChl self-assemblies in silicate capsules exhibited visible absorption and circular dichroism spectra similar to the corresponding natural light-harvesting systems (chlorosomes) of green sulfur bacteria. Dynamic light scattering measurements indicated that the silicate capsules had an average hydrodynamic diameter of several hundred nanometers. BChl self-aggregates in silicate capsules were significantly stable to a nonionic surfactant Triton X-100, which was apt to decompose the BChl aggregates to their monomeric form, compared with conventional micelle systems. BChls in silicate capsules were more tolerant to demetalation of the central magnesium under acidic conditions than the natural systems. 相似文献
9.
Temperature and solvent effects on reaction center structures were examined in two thermophilic photosynthetic bacteria, Chloroflexus aurantiacus and Chromatium tepidum, in order to gain insight into the interactions among the reaction center proteins and pigment systems. Thermal stability of the reaction centers was found to be proportional to the optimum growth temperature. Circular dichroism (CD) spectra in the 250-300 nm region indicated that thermal denaturation destroyed tertiary structures (helix-to-helix interactions or amino acid residue conformation) in the native reaction center, keeping helical structures intact. Absorption and circular dichroism spectral changes showed that alcohol denatured the so-called special pair and the accessory BChl a independently. The alcohol denaturation further indicates that the coordination between BChl a and amino acid residue in the protein is one of the important interactions maintaining the pigment organization of the reaction centers. 相似文献
10.
We have studied the pigment arrangement in purified cytoplasmic membranes of the thermophilic green bacterium Chloroflexus aurantiacus. The membranes contain 30–35 antenna bacteriochlorophyll a molecules per reaction center; these are organized in the B808–866 light-harvesting complex, together with carotenoids in a 2:1 molar ratio. Measurements of linear dichroism in a pressed polyacrylamide gel permitted the accurate determination of the orientation of the optical transition dipole moments with respect to the membrane plane. Combination of linear dichroism and low temperature fluorescence polarization data shows that the Qy transitions of the BChl 866 molecules all lie almost perfectly parallel to the membrane plane, but have no preferred orientation within the plane. The BChl 808 Qy transitions make an average angle of about 44° with this plane. This demonstrates that there are clear structural differences between the B808–866 complex of C. aurantiacus and the B800–850 complex of purple bacteria. Excitation energy transfer from carotenoid to BChl a proceeds with about 40% efficiency, while the efficiency of energy transfer from BChl 808 to BChl 866 approaches 100%. From the minimal energy transfer rate between the two spectral forms of BChl a, obtained by analysis of low temperature fluorescence emission spectra, a maximal distance between BChl 808 and BChl 866 of 23 was derived.Abbreviations BChl
bacteriochlorophyll
- BPheo
bacteriopheophytin
- CD
circular dichroism
- LD
linear dichroism
- Tris
Tris(hydroxymethyl)aminomethane 相似文献
11.
Melkozernov Alexander N. Olson John M. Li Yi-Fen Allen James P. Blankenship Robert E. 《Photosynthesis research》1998,56(3):315-328
Linear and circular dichroism spectra of isolated bacteriochlorophyll a proteins (FMO proteins) and membrane vesicles containing FMO protein from the green sulfur bacterium Chlorobium tepidum were measured at room temperature and 77 K. The orientation of membranes and isolated FMO protein was obtained by gel squeezing. Linear dichroism (LD) data indicate that isolated FMO protein and membrane vesicles associated with the FMO protein are oriented in a similar way in a squeezed polyacrylamide gel. Both samples show a characteristic negative LD band around 814 nm with flanking positive bands at 802 and 824 nm ascribed to the Qy excitonic transitions of BChl a of the FMO protein. This confirms that the C3 symmetry axis of the trimer is perpendicular to the membrane plane, which is supported by the model of the disc-like structure of FMO protein trimers of Cb. tepidum [Li Yi-Fen, Zhou W, Blankenship RE, and Allen JP (1997) J Mol Biol 272: 456–471]. The LD data are consistent with either BChl 3 or 6, but not 7 as the principal contributor to the low temperature band at 825 nm. The low temperature linear and circular dichroism spectra of FMO protein trimers from Chlorobium tepidum show significant differences from the low temperature LD and CD spectra of FMO protein trimers from Prosthecochloris aestuarii. The data are interpreted in terms of somewhat different pigment-protein and pigment-pigment interactions in the two complexes. 相似文献
12.
Structural features of bacteriochlorophyll (BChl) a that are required for binding to the light-harvesting proteins of Rhodospirillum rubrum were determined by testing for reconstitution of the B873 or B820 (structural subunit of B873) light-harvesting complexes with BChl a analogues. The results indicate that the binding site is very specific; of the analogues tested, only derivatives of BChl a with ethyl, phytyl, and geranylgeranyl esterifying alcohols and BChl b (phytyl) successfully reconstituted to form B820- and B873-type complexes. BChl analogues lacking magnesium, the C-3 acetyl group, or the C-13(2) carbomethoxy group did not reconstitute to form B820 or B873. Also unreactive were 13(2)-hydroxyBChl a and 3-acetylchlorophyll a. Competition experiments showed that several of these nonreconstituting analogues significantly slowed BChl a binding to form B820 and blocked BChl a-B873 formation, indicating that the analogues may competitively bind to the protein even though they do not form red-shifted complexes. With the R. rubrum polypeptides, BChl b formed complexes that were further red-shifted than those of BChl a; however, the energies of the red shifts, binding behavior, and circular dichroism (CD) spectra were similar. B873 complexes reconstituted with the geranylgeranyl BChl a derivative, which contains the native esterifying alcohol for R. rubrum, showed in-vivo-like CD features, but the phytyl and ethyl B873 complexes showed inverted CD features in the near infrared. The B820 complex with the ethyl derivative was about 30-fold less stable than the two longer esterifying alcohol derivatives, but all formed stable B873 complexes. 相似文献
13.
Positive and negative bands in previously measured circular dichroism (CD) spectra of Chlorobium limicola chlorosomes appeared to be sign-reversed relative to those of Chloroflexus aurantiacus chlorosomes in the 740–750 nm spectral region where bacteriochlorophyll (BChl) c absorbs maximally. It was not clear, however, whether this difference was intrinsic to the chlorosomes or was due to differences in the procedures used to prepare them. We therefore repeated the CD measurements using chlorosomes isolated from both Cb. limicola f. thiosulfatophilum and Cf. aurantiacus using the method of Gerola and Olson (1986, Biochim. Biophys. Acta 848: 69–76). Contrary to the earlier results, both types of chlorosomes had very similar CD spectra, suggesting that both have similar arrangements of BChl c molecules. The previously reported difference between the CD spectra of Chlorobium and Chloroflexus chlorosomes is due to the instability of Chlorobium chlorosomes, which can undergo a hypsochromic shift in their near infrared absorption maximum accompanied by an apparent inversion in their near infrared CD spectrum during isolation. Treating isolated chlorosomes with the strong ionic detergent sodium dodecylsulfate, which removes BChl a, does not alter the arrangement of BChl c molecules in either Chloroflexus or Chlorobium chlorosomes, as indicated by the lack of an effect on their CD spectra.Abbreviations BChl
bacteriochlorophyll
-
Cb.
Chlorobium
- CD
circular dichroism
-
Cf.
Chloroflexus
- NIR
near infrared 相似文献
14.
V I Grosheva 《Antibiotiki i khimioterapii͡a》2006,51(2):3-7
Analysis of circular dichroism spectra made it possible to offer a method for estimation of tetracycline solutions contamination with metal ions. By its sensitivity the method is much superior to the spectrophotometric one used at present for determination of the antibiotic purity. In the latter method formation of complexes with metals is traced by batochromic displacement of the absorption spectra. The new method is rapid, relatively selective and requires comparatively small quantities of the substance for the analysis, which provides its use under both laboratory and manufacture conditions. The method is based on identification of the circular dichroism spectra of tetracycline complexes with metals in the long wavelength region. The presence of the circular dichroism concervative bands with strictly defined extremums in the spectra of tetracycline low acid solutions contaminated by multiply charged metal ions allowed vs. the circular dichroism spectra of pure tetracycline sample to conclude that the solution contained admixtures and to suggest their nature. It was shown that the charge, ion radius and tetracycline:metal relation were the factors defining the mark and location of the dichroism band extremums. At lambda(extr)-410-415 nm the tetracycline complexes with light metal ions such as Mg2+, Al3+ and Ca2+ were detected by the circular dichroism negative band in the spectra, while the complexes with heavy metal ions such as Sc3+, Sr3+, Cu3+, Cd3+, Ba2+, Y3+ and the cerium subgroup lanthanides were detected by the circular dichroism positive band. The tetracycline complexes with the lanthanides of the second half of the yttrium subgroup (Ho(3+)-Lu3+) were characterized by the presence of the circular dichroism minimum at lambda(min)-425 nm. When the tetracycline concentration was above 1.5 x 10(-3) M, multiligand complexes with circular dichroism negative extremum at lambda(min)-400 nm formed. 相似文献
15.
The effect of temperature on the aggregation of 3lR-8,12-diethyl farnesyl bacteriochlorophyll c in a mixture of n-pentane and methylcyclohexane (1/1, v/v) was studied by means of absorption, circular dichroism and fluorescence spectroscopy. At room temperature essentially only two aggregate species, absorbing at 702 nm (A-702) and 719 nm (A-719), were present. Upon cooling to 219 K, A-702 was quantitatively converted to A-719. Further lowering of the temperature led to the stepwise formation of larger aggregates by the conversion of A-719 to aggregate species absorbing at 743 nm (A-743) and 755 nm (A-755). All absorption changes were reversible. A-719 was highly fluorescent (maximum at 192 K: 744 nm), while A-743 and especially A-755 were weakly fluorescent. Below 130 K the mixture solidified, and no major changes in the absorption spectrum were observed upon further cooling. At 45 K, however, a relatively strong emission at 775 nm was observed. Below 200 K, the absorption, fluorescence and circular dichroism spectra resembled that of the chlorosome. These results open up the possibility to study higher aggregates of BChl c as models for the chlorosome by various methods at low temperature, thus avoiding interference by thermal processes.Abbreviations A-680, A-702, A-719, A-743 and A-755-
BChl c aggregates absorbing at the wavelengths indicated
- BChl-
bacteriochlorophyll
- R[E,E] BChl c
F-
the 31 R isomer of 8,12-diethyl BChl c esterified with farnesol (F), analogously
- M-
methyl
- Pr-
propyl
- S-
stearol (see Smith 1994)
- CD-
circular dichroism 相似文献
16.
Three homologs of BChl c, 2-(R)-(1-hydroxyethyl)-4-n-propyl-5-ethyl-farnesyl BChl c (PEF-BChl c), 2-(R)-(1-hydroxyethyl)-4-ethyl-5-ethyl-farnesyl BChl c (EEF-BChl c), and 2-(S)-(1-hydroxyethyl)-4-isobutyl-5-methyl/ethyl-farnesyl BChl c (iBM/EF-BChl c), formed aggregates in water-saturated carbon tetrachloride (H2O-satd CCl4). The water content was about 100 times higher than that of the dried CCl4 previously used. Absorption spectra were recorded for 8 concentrations for the three homologs of BChl c and were deconvoluted in terms of standard spectra of monomer, dimer, tetramer and polymer (747-nm aggregate, Olson and Pedersen (1990) Photosynthe Res 25: 25). PEF- and EEF-BChl c formed dimers (680 nm maximum) and tetramers (705–710 nm maximum), but iBM/EF-BChl c formed polymers. Inhibition of dimer formation by water faciliated the study of the initial stages of the polymerization of BChl c. When the logarithm of polymer concentration was plotted versus the logarithm of the monomer concentration for iBM/EF-BChl c, the initial slope was 30±10 and indicated the cooperation of 20–40 BChl c molecules to form a polymer from a seed. Circular dichroism spectra of the polymers with positive and negative bands at 743 and 760 nm, respectively, were similar to those for chlorosomes (Brune et al. (1990) Photosynth Res 24: 253).Abbreviations BChl
bacteriochlorophyll
- CD
circular dichroism
- EEF
4-ethyl-5-ethyl farnesyl
- iBM/EF
4-isobutyl-5-methyl/ethyl farnesyl
- H2O-satd CCl4
water saturated carbon tetrachloride
- PEF
4-n-propyl-5-ethyl farnesyl 相似文献
17.
The intermediate in the equilibrium unfolding of canine milk lysozyme induced by a denaturant is known to be very stable with characteristics of the molten globule state. Furthermore, there are at least two kinetic intermediates during refolding of this protein: a burst-phase (first) intermediate formed within the dead time of stopped-flow measurements and a second intermediate that accumulates with a rate constant of 22 s(-)(1). To clarify the relationships of these intermediates with the equilibrium intermediate, and also to characterize the structural changes of the protein during refolding, here we studied the kinetic refolding reactions using stopped-flow circular dichroism at 10 different wavelengths and obtained the circular dichroism spectra of the intermediates. Comparison of the circular dichroism spectra of the intermediates, as well as the absence of observed kinetics in the refolding from the fully unfolded state to the equilibrium intermediate, has demonstrated that the burst-phase intermediate is equivalent to the equilibrium intermediate. The difference circular dichroism spectrum that represented changes from the kinetic intermediate to the native state had characteristics of an exciton coupling band, indicating that specific packing of tryptophan residues in this protein occurred in this phase. From these findings, we propose a schematic model of the refolding of canine milk lysozyme that is consistent with the hierarchical mechanism of protein folding. 相似文献
18.
Spectroscopic characterization of the light-harvesting complex of Rhodospirillum rubrum and its structural subunit 总被引:4,自引:0,他引:4
The spectroscopic properties of the light-harvesting complex of Rhodospirillum rubrum, B873, and a detergent-isolated subunit form, B820, are presented. Absorption and circular dichroism spectra suggest excitonically interacting bacteriochlorophyll alpha (BChl alpha) molecules give B820 its unique spectroscopic properties. Resonance Raman results indicate that BCHl alpha is 5-coordinate in both B820 and B873 but that the interactions with the BChl C2 acetyl in B820 and B873 are different. The reactivity of BChl alpha in B820 in light and oxygen, or NaBH4, suggests that it is exposed to detergent and the aqueous environment. Excited-state lifetimes of the completely dissociated 777-nm-absorbing form [1.98 ns in 4.5% octyl glucoside (OG)], the intermediate subunit B820 (0.72 ns in 0.8% OG), and the in vivo like reassociated B873 (0.39 ns in 0.3% OG) were measured by single-photon counting. The fluorescence decays were exponential when emission was detected at wavelengths longer than 864 nm. An in vivo like B873 complex, as judged by its spectroscopic properties, can be formed from B820 without the presence of a reaction center. 相似文献
19.
Joseph Kuo-Hsiang Tang Semion K. Saikin Sai Venkatesh Pingali Miriam M. Enriquez Joonsuk Huh Harry A. Frank Volker S. Urban Alán Aspuru-Guzik 《Biophysical journal》2013
Green photosynthetic bacteria adjust the structure and functionality of the chlorosome—the light-absorbing antenna complex—in response to environmental stress factors. The chlorosome is a natural self-assembled aggregate of bacteriochlorophyll (BChl) molecules. In this study, we report the regulation of the biogenesis of the Chlorobaculum tepidum chlorosome by carbon assimilation in conjunction with temperature changes. Our studies indicate that the carbon source and thermal stress culture of C. tepidum grows slower and incorporates fewer BChl c in the chlorosome. Compared with the chlorosome from other cultural conditions we investigated, the chlorosome from the carbon source and thermal stress culture displays (a) smaller cross-sectional radius and overall size, (b) simplified BChl c homologs with smaller side chains, (c) blue-shifted Qy absorption maxima, and (d) a sigmoid-shaped circular dichroism spectra. Using a theoretical model, we analyze how the observed spectral modifications can be associated with structural changes of BChl aggregates inside the chlorosome. Our report suggests a mechanism of metabolic regulation for chlorosome biogenesis. 相似文献
20.
Reaction center (RC) complexes isolated from a Zn-bacteriochlorophyll (BChl) a-containing purple bacterium, Acidiphilium rubrum, were characterized by absorption, circular dichroism, and magnetic circular dichroism (MCD) spectroscopy. The oxidized-minus-reduced difference spectra indicated that, in this RC, the Zn-BChl a is the primary electron donor. The molecular structure of the donor was examined by measuring the ratio of the MCD intensity of the Faraday B-term (B) to the dipole strength (D). In the Q(y) region, B/D for the donor was about half those of bacteriopheophytin a and the accessory Zn-BChl a, indicating that the primary electron donor is a dimer. The magnitude of bleach of the Q(x) band was half that observed in Rhodobacter sphaeroides, suggesting the cation is localized on a single Zn-Bchl a. The absorption intensity of the higher-energy Q(y) exciton band was approximately 28% of that of the lower-energy band, and the exciton splitting was approximately 570 cm(-1), smaller than that in Rb. sphaeroides. These results indicate that, in A. rubrum, the primary electron donor is a Zn-BChl a dimer but that the interaction between the two molecules is rather weak. On the basis of these results, an adaptive strategy for changes in BChl a species is discussed from an evolutionary perspective. 相似文献