ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb02244.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe present study describes the construction of aRhodobacter sphaeroideslight‐harvesting (LH2) mutant in which the charged residueβSLys23 is changed by site‐directed mutagenesis to a Gin residue, and the characterization of the resulting mutant complex by a range of spectroscopic techniques. In the 77 K absorption spectrum of the mutant, the peak equivalent to the 850 nm peak in the wild‐type membrane is blue‐shifted by approximately 18 nm to 837 nm; except for this blue‐shift, the 77 K. fluorescence excitation and emission spectra and the circular dichroism spectrum of the mutant are very similar to the equivalent spectra from the wild‐type membranes, suggesting that the mutation βLys23 → Gin probably does not cause any major changes in the conformation or aggregation state of these membranes. Possible causes of the 18 nm blue‐shift in the absorption spect

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb02245.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe spectral effects of a number of endo‐ and exoproteases to the detergent‐solubilized antenna complexes B802–858(sphaeroideslike) of strainRhodopseudomonas acidophila10050 and B802–824of strain 7050 were analyzed. Upon protease digestion the time course of spectral modification between 250 and 900 nm was recorded. In addition, circular dichroism (CD) signals were measured between 450 and 950 nm. The endoprotease elastase as well as the exoprotease carboxypeptidase A (CP A) altered the B802–858antenna complex, by changing the 858 nm band hypochromically (30‐50%) with an additional small hypsochromic shift (3–6nm). A combined carboxypeptidase digestion,e.g.CP A and CP B, yielded a further modification to a complex with absorption bands at 800 nm and ˜840 nm (ε˜ 50% of the 800 nm band). By exposing the isolated B803–824antenna complex to the different proteases no significant spectral change was observed. The B802–858antenna complex, modified by CP A, exhibits a60–70% decrease of the biphasic CD signal in the near infrared. The limited proteolysis experiments provide conclusive experimental evidence that the C‐terminal domains of the antenna polypeptides α and β contribute to the formation of (dimeric) bacteriochlorophyll (BChl)amolecules absorbing at around 850 nm. This agrees with the hypothesis, based on comparative amino acid sequence analysis, that in purple bacterial antenna complexes the structural requirements (specific amino acids in the vicinity of the BChl molecules,e.g.aromatic amino acids) for batho‐ and hyperchromicity of BChl molecules apparently reside to a considerable extent in the C‐terminal portion

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb02246.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractFluorescence lifetimes of isolated membranes ofRhodopseudomonas viridiswere measured in the temperature range of 77 K to 25 K. At room temperature, the main component of the fluorescence decay of bacteriochloro‐phyll (BChl)bhad a time constant of 50 ps. In contrast to other purple bacteria, the emission at low temperature was spectrally homogeneous and showed essentially single lifetimes of 140 ps at 77 K and 180 ps at 25 K, with the primary electron donor in the oxidized state. Taking into account the relative fluorescence yields with open and closed reaction centers, we arrive at numbers of 125 ps and 215 ps, respectively, for open reaction centers. These numbers are significantly smaller than expected on the basis of measurements of the efficiency of charge separation, perhaps suggesting that the excitation decay in the absence of reaction centers is considerably faster at low temperature than at room temperature. At least four different spectral components with different lifetimes were observed at 25 K in the emission ofHeliobacterium chlorum,a short‐wavelength component of about 30 ps and three longer‐wavelength components of about 100 ps, 300 ps, and 900 ps. This indicates a strong heterogeneity in the emitting pigment, BChl g‐808. The component with the shortest lifetime does not appear to be affected by the redox state of the reaction center and might reflect energy transfer to BChlgspecies which are connected to the reaction

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb02247.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract–Triplet‐minus‐singlet (T‐S) spectra and singlet‐triplet annihilation was measured onRhodospirillum rub‐rumchromatophores at low temperatures (4–77K). The T‐S spectrum of the LH‐1 antenna was dependent on the wavelength of excitation and thus indicative of site‐inhomogeneous broadening. The data cannot be understood adequately using the two pigment pool model (B880 + B896) but, in contrast, support a model for LH‐1, in which the spectral properties are determined by site‐inhomogeneous broadening. Consequently, the 4 K antenna domain for singlet‐triplet annihilation in LH‐1 is rather small. If the temperature is raised to 77 K the annihilation domain increases, and a fit of the fluorescence quenching and triplet yield data suggests that at 77 K the connectivity is between the extreme cases of the “lake” and the isolated “puddles” models. The implications of the observed antenna inhomogeneity on low temperature annihilation and fluo

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb02248.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractNonlinear polarization spectroscopy in the frequency domain allows rate constant determinations of fast electronic energy and phase relaxations together with characterization of the type of line broadening. Application of this method to the B850 component of the isolated B800–850antenna ofRhodobacter sphaeroidesat room temperature shows that B850 is inhomogeneously broadened, with homogeneous widths between 30 and 200 cm−1, depending on the spectral position of the subforms. The corresponding phase relaxation times are clearly in the subpicosecond range. There is also indication of an up‐to‐now unspecified1–5 ps energy relaxation channel pe

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb02249.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractFluorescence decay curves are calculated within the framework of the Liouville von Neumann equation for simple model systems of a photosynthetic unit consisting of a reaction center coupled to either a linear chain or a hexagonal array of identical antenna pigments. A comparison of the results with those obtained by solving the Pauli Master equations reveals that in the case of coherent excitation energy transfer the fluorescence decay kinetics exhibit a strong dependence on the topological array of the antenna pigments. For systems with a different pigment array, markedly different kinetics can be expected upon decreasing the pure dephasing time.

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb02250.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractDetailed burn wavelength‐dependent hole‐burning studies of the title complex have been performed. The zero‐phonon hole (ZPH) widths for B800 at 4.2 K are 6.0 ± 0.3 cm and are discussed in terms of B80O‐B850 and B800‐B800 energy transfer. The B800* lifetime is 1.8 ± 0.2 ps. The site inhomogeneous broadening (r,) of B800 is 240 cm−1. The B850 (located at 864 nm at 4.2 K) hole spectra reveal that B850 suffers from significant homogeneous broadening, which is attributed to unit cell exciton level structure and ultrafast interexciton level relaxation. Novel ZPH action spectra lead to the resolution of a minor component at 885 nm, which is the analogue of B870 ofRhodobacter sphaeroidespreviously assigned as the lowest exciton level of the B850 exciton band. The B870 ZPH width of 2.0 ± 0.2 cm−1for Rhodopseudomonas acidophilaleads to a total dephasing time of 5.3 ps, which is attributed to exciton scattering that stems from the energetic inequivalence of neighboring

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb02251.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractPolarization properties of the fluorescence from a pair of identical molecules coupled electronically are examined on the basis of a stochastic Liouville equation formalism developed in 1979 by Rahman, Knox and Kenkre. The time development of polarization is calculated for random ensembles of rigid molecule pairs under initial conditions that represent either selective excitation or broad‐band coherent excitation. We hold that the applicability of the Forster mechanism is not limited to cases of weak coupling, and we indicate the rationale and a method for observing it in cases involving large interaction between transition dipole

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb02252.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe location of the carotenoid 2Ag‐state (S1) was studied by fluorescence spectroscopy in two series of carotenoids. One consisted of natural polyenes like phytoene, phytofluene, β‐carotene, and neurosporene, and the other of minicarotenes,i.e.,compounds similar to β‐carotene, but with a smaller number of double bonds(n=3–9). A decrease of the S1‐S0energy gap withnwas observed in both series, and extrapolation ton= 11 gave the energies 14 500 and 13 200 cm−1for β‐carotene and lycopene, respectively. The neurosporene S1state was located atca16 000 cm−1. A good relationship between the nonradiative relaxation rate and the number of conjugation was observed. The rate increased by a factor of 2.5 per double bond. The possible role of the S1state in reversible carotenoid ← chlorophyll electron‐exchange energy

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb02253.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY