摘要:

AbstractFour carotenoids, 3,4,7,8‐tetrahydrospheroidene, 3,4,5,6‐tetrahydrospheroidene, 3,4‐dihydrospheroidene and spheroidene, have been incorporated into the B850 light‐harvesting complex of the carotenoidless mutant, photosynthetic bacterium,Rhodobacter sphaeroidesR‐26.1. The extent of π‐electron conjugation in these molecules increases from 7 to 10 carbon‐carbon double bonds. Carotenoid‐to‐bacteriochlorophyll singlet state energy transfer efficiencies were measured using steady‐state fluorescence excitation spectroscopy to be 54 ± 2%, 66 ± 4%, 71 ± 6% and 56 ± 3% for the carotenoid series. These results are discussed with respect to the position of the energy levels and the magnitude of spectral overlap between the S, (2′AJ state emission from the isolated carotenoids and the bacteriochlorophyll absorption of the native complex. These studies provide a systematic approach to exploring the effect of excited state energies, spectral overlap and excited state lifetimes on the efficiencies of carotenoid‐to‐bacteriochlorophyll singlet energy tran

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb02254.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractResonance‐enhanced coherent anti‐Stokes Raman spectra are recorded for monomers and trimers of phycocyanin from three different cyanobacteria:Westiellopsis prolifica, Mastigocladus laminosusandSpirulina platensis.It is shown that upon aggregation from monomer to trimer the electronic structures of both the α84 and β84 chromophores are changed. The spectra of the trimers originating fromS. platensisandM. laminosusare very similar to each other, but distinctly different from the spectrum ofW. prol

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb02255.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe ground and excited state properties of two regions in the Δ15‐configurational space of the phycoviolobilin chromophore in the α‐subunit of phycoerythrocyanin are analyzed. Molecular dynamics calculations reveal that the chromophore geometry determines the active‐site dynamics. The excited state torsional potential surface shows a negative barrier for isomerization and trapping of an activated complex. Strong coupling of excited states localized in the chromophore and charge transfer states from the surrounding polar residues provides favorable prerequisites for fast excited state surface crossing in competition with other deactivation processes. The formation of a photoreduced intermediate following the photoinduced charge transfer may trigger subsequent chemical re

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb02256.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractTwo phycoerythrocyanin (PEC) fractions have been obtained from the phycobilisomes of the cyanobac‐teriumWestiellopsis prolificaARM 365. They have been characterized by absorption, fluorescence and circular dichroism spectroscopy. One of them is spectroscopically similar to a PEC trimer known from other organisms. Whereas efficient energy transfer from its violin (α‐84) to the cyanin (β‐84, 155) chromophores is efficient in the trimer (αβ it is impeded after dissociation to the monomer (α,β). A second fraction of PEC which we earlier termed PEC(X) (Maruthi Saiet al., Photochem. Photobiol.55,119–124, 1992), exhibited the spectral properties similar to that of the α‐subunit of PEC fromMastigocladus laminosus.With this highly photoactive fraction, the circular dichroism spectra of the violobilin chromophore in both photoreversible stat

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb02257.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe excited state dynamics of trimeric phycoerythrocyanin has been studied by two‐color femtosecond transient absorption spectroscopy with a time‐resolution better than 200 fs. Upon selective excitation of the short‐wavelength phycobiliviolin chromophore at 575 nm absorption bleachings are observed. An isotropic ultrafast decay of the initial bleaching of 585 ± 40 fs has been resolved at short detection wavelength (578 nm). Upon stepwise increase of the detection wavelength up to 617 nm, the bleaching showed a delayed rise above 593 nm with rrice=380–580 fs. All other isotropic kinetic components in this wavelength range were longer than 100 ps. The ultrafast component is discussed in terms of an energy transfer process from the α‐84 phycobiliviolin chromophore to the β‐84 chromophore in adjacent monomer subunits of the trimer. It is concluded that the β‐155 chromophore is the longest‐wavelength chromophore. Exciton relaxation between closely spaced chromophore pairs is discussed as an alternative interpretation for the

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb02258.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe time‐resolved luminescence spectra (in the microsecond range) of phycobilisomes and biliproteins in buffer and polymer matrix were measured in the temperature range from 8 K. to 293 K. Delayed luminescence located in the same spectral region as prompt fluorescence of investigated samples (DLF) and the long‐wavelength delayed emission in the720–760 nm range (DL1) was observed. The temperature and viscosity dependencies of DLF and DL1 luminescences were different, but both do not have uniexponential decays and are not quenched by oxygen. This means that delayed luminescence could be generated without the participation of the triplet states, or the chromophores could be shielded by protein against interaction with oxygen. The linear dependence of delayed luminescence on exciting light intensity shows that delayed luminescence is monophotonically induced.It seems that both DLF and DL1 are related to electron‐cation recombination, which yields excited singlet states. The DLF is emitted from the first excited singlet state of biliprotein chromophores and DL1 from the same state of the excimers or from the triplet state of some groups of chromophores. Ionization energy of chromophores can be lowered as a result of their interactions with the environment. Delay of emission is due to the trapping or solvation of electrons. Every type of biliprotein consisting of phycobilisomes possesses its own “trap” and can emit the DL. In the case of native phycobilisomes a competition between the excitation energy trapping and tran

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb02259.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractRecently, reasonable spectral simulations of the experimental low‐temperature absorption and circular dichroism (CD) spectra of the bacteriochlorophyll (BChl)aprotein fromProsthecochloris aestuariiwere produced for the unaggregated protein trimer based on standard assumptions regarding QYtransition moment directions. We report here significant improvements of these simulations, obtained by computer search of unknown parameters including the site wavelengths of the individual BChl and exciton‐transition line widths. Absorption and CD spectra are fit with a common set of search parameter values. As before, calculated exciton‐transition wavelengths and line widths also compare favorably with values deduced from laser hole‐burning experiments. However, the improved simulations are only obtained when comparison is made to 77 K data obtained with a cryosolvent containing glycerol but not glycerophosphate. Simulations of 77 K data obtained with a mixture of glycerol and glycerophosphate are poorer than those recently reported. (The latter are based on 5 K absorption and 77 K CD data, with transition line widths independently selected for each simulation.) Computer tests of the search routine demonstrate that these results are independent of the routine itself. A possible explanation is that the glycerophosphate‐containing cryosolvent perturbs the protein structure enough to alter slightly the inter‐BC

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb02260.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractSpectral forms of bacteriochlorophyll (Bchl) in chlorosomes were analyzed by linear dichroism, circular dichroism (CD), and deconvolution of these spectra. Isolated chlorosomes were embedded in polyacrylamide gels and compressed unidirectionally (along the x‐axis) while allowing the gel to stretch in another direction (along the z‐axis). The chlorosomes were aligned three‐dimensionally due to their flat oblong shape; the longest axis was presumed to parallel the z‐axis, its shortest axis was presumed to parallel the x‐axis, and the intermediate‐length axis was presumed to parallel the y‐axis. Degrees of polarization (AI− A1)/(AI+ A1) of Bchlcandameasured from the y‐axis with linearly polarized light were significantly different from those measured from the x‐axis. Deconvolution of spectra into components revealed the presence of two major forms of Bchlcwith peaks at 744 nm and 727 nm. The degrees of polarization of the 744 and 727 nm spectral forms were 0.76 and 0.59 from the y‐axis and 0.48 and 0.39 from the x‐axis, respectively. The degrees of polarization of Bchl a794 were –0.21 from the y‐axis and 0.12 from the x‐axis. These values indicate that the direction of the Qytransition moment of Bchl c744 is almost completely parallel to the longest axis of chlorosomes and that of Bchl c727 is also nearly, but slightly less so, parallel to the longest axis of the chlorosomes. The Qytransition moment of the baseplate Bchlapeak at 794 nm is nearly perpendicular to the longest axis and parallel to the shortest axis: that is, it is perpendicular to the associated membrane plane in the cell. These alignments of Bchl transition moments in chlorosomes were lost after suspending the chlorosomes in a solution saturated with 1‐hexanol accompanying a shift in the peak position from 742 nm to 670 nm. The alignment recovered after the hexanol concentration was decreased. The presence of two major spectral forms of Bchlcwas supported by the deconvolution of CD

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb02261.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractChlorosomes isolated fromChloroflexus aurantiacuswere extracted with chloroform/methanol. The extract contained bacteriochlorophyllscandaand lipids, but was devoid of proteins. This crude extract spontaneously formed aggregates when a methanol solution was dispersed in aqueous buffer.The aggregates could be sedimented by ultracentrifugation and appeared in electron micrographs as stain‐excluding bodies with diameters between 70 and 170 nm. The absorption spectrum is remarkably similar to that of intact chlorosomes with an absorption maximum of bacteriochlorophyllcat around 740 nm. The circular dichroism spectrum of the aggregate is also very similar to that of intact chlorosomes. A conservative (±) band centered at 740 nm confirms the highly aggregated state of bacteriochlorophyllcin both systems.Steady‐state fluorescence studies showed that in the aggregate energy‐transfer from bacteriochlorophyllcto a component emitting at 830 nm took place. When the aggregate was suspended in buffer saturated with 1‐hexanol the 740 nm form of bacteriochlorophyllcwas reversibly converted to a form with spectral properties resembling the monomer absorbing at 670 nm but still in an aggregated state. This form of bacteriochlorophyll c showed no circular dichrois

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb02262.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe efficiency of energy transfer from the peripheral chlorosome antenna structure to the membrane‐bound antenna in green sulfur bacteria depends strongly on the redox potential of the medium. The fluorescence spectra and lifetimes indicate that efficient quenching pathways are induced in the chlorosome at high redox potential. The midpoint redox potential for the induction of this effect in isolated chlorosomes fromChlorobium vibrioformeis ‐146 mV at pH 7(vsthe normal hydrogen electrode), and the observed midpoint potential (n = 1) decreases by 60 mV per pH unit over the pH range7–10. Extraction of isolated chlorosomes with hexane has little effect on the redox‐induced quenching, indicating that the component(s) responsible for this effect are bound and not readily extractable. We have purified and partially characterized the trimeric water‐soluble bacteriochlorophyll a‐containing protein from the thermophilic green sulfur bacteriumChlorobium tepidum.This protein is located between the chlorosome and the membrane. Fluorescence spectra of the purified protein indicate that it also contains groups that quench excitations at high redox potential. The results indicate that the energy transfer pathway in green sulfur bacteria is regulated by redox potential. This regulation appears to operate in at least two distinct places in the energy transfer pathway, the oligomeric pigments in the interior of the chlorosome and in the bacteriochlorophyllaprotein. The regulatory effect may serve to protect the cell against superoxide‐induced damage when oxygen is present. By quenching excitations before they reach the reaction center, reduction and subsequent autooxidation of the low potential electron acceptors found in these organis

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb02263.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY