ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1996.tb02413.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractThe reaction center (RC) of green sulfur bacteria belongs to the Fe‐S type RC, as do the photosystem I of oxygenic photosynthetic organisms and the RC of heliobacteria. The core parts of the green sulfur bacterial and the heliobacterial RC are assumed to be homodimeric, in contrast to those of purple bacteria, photosystem I and photosystem II. This paper describes recent advances in the study of the function of the green sulfur bacterial R

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1996.tb02414.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractMembranes ofChlorobium tepidumcontain about 35, 45 and2–10 molecules of menaquinone‐7, chlorobium quinone (1′‐oxo‐menaquinone‐7) and of the polar menaquinone (probably 1′‐OH‐menaquinone‐7) per reaction center, respectively. None of these quinones was retained during the isolation of P840‐reaction centers beyond the detection limit of about 0.2 quinones per reaction center, neither in the core complex nor in functionally intact reaction center preparations. The latter is shown to catalyze the formation of an electrochemical proton gradient in the presence of ascorbate and phenazinium methosulfate, when it is incorporate

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1996.tb02415.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractThe electronic structure of the oxidized primary chlorophyll electron donor, P840+., of the green sulfur bacteriumChlorobium limicolahas been investigated using electron spin echo envelope modulation (ESEEM) spectroscopy. This ESEEM investigation of the electron spin density distribution in the radical cation P840+.in membranes isolated fromC. limicolaconfirms that the electron spin is shared eqully between the two bacteriochlorophyllamolecules. Observation of the small hyperfine couplings to the ring nitrogens by ESEEM gives results that are in agreement with those obtained from ENDOR measurements (S. E. J. Rigby, R. Thapar, M. C. W. Evans and P. Heathcote,FEBS Lett.350,24–28, 1994) of the large hyperfine couplings to the methyl group protons. These results in combination with the Raman spectroscopy of P840 (U. Feiler, D. Albouy, B. Robert and T. A. Mattioli,Biochemistry34,11099–11105, 1995) all indicate that the reaction center of green sulfur photosynthetic bacteria is functionally a protein homodimer providing a symmetrical protein environment for the primary electron do

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1996.tb02416.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractTime‐resolved absorbance changes were measured in isolated membranes, depleted of chlorosomes, and in the Fenna‐Matthews‐Olson (FMO) complex of the green sulfur bacteriumProsthecochloris aestuarri.The isolated FMO complex showed a biphasic decay of excited bacteriochlorophylla(BChla) with time constants of about 80 and 1400 ps. Approximately the same time constants were observed upon excitation of isolated membranes together with a component of about 30 ps. It is concluded that the efficiency of energy transfer from the FMO to the core complex is very low, in agreement with earlier measurements of the efficiency of charge separation. The 30 ps decay component is ascribed to trapping of the excitation energy from the core BChlaby the reaction c

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1996.tb02417.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractTransient absorption difference spectroscopy was used to study the temperature dependence of the P798+decay kinetics in heliobacteria. For membrane samples, two components were obtained from the fitting of kinetic traces in the temperature range of4–29°C. A3–9 ms component representing the cytochrome (cyt)coxidation has an activation energy of 33.0 ± 2.8 KJ/mol. A12–22 ms component representing either P798+Fx‐ or P798+FA/Brecombination has an activation energy of 15.3 ± 2.4 KJ/mol. In isolated reaction centers (RC), only one 14 ms component due to P798+Fx‐ recombination was obtained in this temperature range. The Arrhenius plot shows that the recombination rate of this P798+Fx‐ state is temperature independent in the near room temperature range. For RC in the temperature range of60–298 K, a12–15 ms decay was obtained at temperatures greater than 240 K. Biphasic decay traces (12–15ms and2–4 ms components) were obtained at temperatures between 170 K and 230 K. Only one2–4 ms component was found at temperatures lower than 160 K. The gradual switchover from the12–15 ms to the2–4 ms component upon cooling may indicate the shift of the P798+Fx‐ recombination state to a state that is prior to P798+Fx, although other interpretations can not be excluded. The absorption difference spectrum (ΔA@ 160 K ‐ ΔA@ 240 K) in the blue region shows a positive amplitude below 405 nm and a negative amplitude above 405 nm implying that the2–4 ms decay component may be due to the recombination of P798+A1

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1996.tb02418.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractMembrane fragments ofHeliobacillus (Hc.) mobiliswere characterized using resonance Raman (RR) spectroscopy in order to determine the configuration of the neurosporene carotenoid, the pigment‐protein interactions of the bacteriochlorophyll (BChl)gmolecules, and the Chla‐like chlorin pigments present in the antenna‐reaction center complex constituting the photosynthetic apparatus. Using 363.8 nm excitation, the Raman contributions of the BChlgmolecules were selectively resonantly enhanced over those of the carotenoid and the Chla‐like chlorin pigments. The RR spectrum of BChlgin these membranes excited at 363.8 nm exhibits bands at 1614 and 1688 cm−1, which correspond to a CaCmmethine bridge stretching mode and a keto carbonyl group stretching mode, respectively. Both of these bands are 16 cm−1wide (full width at half maximum, FWHM), indicating that a sole population of BChlgmolecules is being enhanced at this excitation wavelength. The observed frequency of the CaCmstretching mode (1614 cm−1) indicates that the bulk of BChlgmolecules is pentacoordinated with only one axial ligand to the central Mg atom while that of the keto carbonyl stretching mode (1668 cm−1) indicates that these groups are engaged in a hydrogen bond. This homogeneous population of BChlgmolecules bound to the heliobacterial core polypeptides is in contrast to the heterogeneous population of Chlamolecules bound to the core polypeptides of the reaction center of photosystem I ofSynechocystis6803 as observed by the inhomogeneously broadened C9keto carbonyl band in its RR spectrum. The RR spectrum of the Chla‐like chlorin pigments inHc. mobilisexcited at 441.6 nm exhibits a broad keto carbonyl band (43 cm−1FWHM) with components at 1665, 1683 and 1695 cm−1, indicating several populations of these pigments differing in their protein interactions at the level of the keto carbonyl group. Fourier transform (FT) pre‐RR spectroscopic measurements of intact whole cells and membrane fragments at room temperature using 1064 nm excitation indicate that high quality vibrational spectra of the BChlgmolecules can be obtained with no photodegradation. Low‐temperature FT Raman spectra excited at 1064 nm reveals an inhomogeneously broadened 1665 cm−1band corresponding to the C9keto carbonyl stretching mode. Spectral deconvolution and second derivative analysis of this band reveal that it is comprised of components at 1665, 1682 and 1695 cm−1, the latter two most likely arising from BChlgphotoconversion products. Excitation using 885 nm to enhance the preresonance effect of the BChlgmolecules yields an FT Raman spectrum where the keto carbonyl band at 1665 cm−1is narrow, as is the case in the Soret RR spectra, reflecting a sole population of BChlgmolecules, which are engaged in an H bond. The RR spectrum of the neurosporene molecule inHc. mobilismembranes excited at 496.5 nm is compared to that of 1,2‐dihydroneurosporene bound in acisconfiguration in reaction centers ofRhodopseudomona viridisand to that of the same carotenoid in its all‐transconfiguration extracted from these reaction centers in the presence of light. The similarity of this latter RR spectrum with that of neurosporene in theHc. mobilismembranes indicates that it is

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1996.tb02419.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractThe PsaA and PsaB polypeptides form the reaction center core heterodimer of photosystem I (PSI). Both PsaA and PsaB are predicted to have 11 hydrophobic domains, although it is unclear how both polypeptides fold within the thylakoid membrane. If all 11 hydrophobic regions form membrane‐spanning domains, the N‐ and C‐terminus must be located on opposite sides of the membrane. The C‐terminus of PsaB is very conserved in a wide range of organisms and may be important for PSI assembly or function. Using chloroplast transformation inChlamydomonas reinhardtiiwe have generated a series of C‐terminal extension and deletion mutants of the PsaB polypeptide. Analysis of these mutants and spontaneous revertants indicates that the C‐terminus may be extended by at least 14 amino acids without impairing PSI assembly. Deletion of amino acids 732–736 also has no impact on PSI, whereas deletion of amino acids 727–736 results in no accumulation of the complex. The site of truncation in the 727–736 deletion coincides with the end of the hydrophobic domain XI supporting a location of the C‐terminus of PsaB on the

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1996.tb02420.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractThepsalandpsaLgenes were characterized from the cyanobacteriumSynechococcussp. strain PCC 7002. The gene organization was different from that reported for other cyanobacteria withpsaloccurring upstream and being divergently transcribed from thepsaLgene. Mutants lacking Psal or PsaL were generated by interposon mutagenesis and characterized physiologically and biochemically. Mutant strains PR6307 (Δpsal−), PR6308 (psal) and PR6309 (psaL−) had doubling times similar to that of the wild type under both high‐ and low‐intensity white light, but all grew more slowly than the wild type in green light. Only monomeric photosystem I (PS I) complexes could be isolated from each mutant strain when Triton X‐100 was used to solubilize thylakoid membranes; however, approximately 10% of the PS I complexes from thepsalmutants, but not thepsaLmutant, could be isolated as trimers whenn‐do‐decyl β‐D‐maltoside was used. Compositional analyses of the mutant PS I complexes indicate that the presence of PsaL is required for trimer formation or stabilization and that Psal plays a role in stabilizing the binding of both PsaL and PsaM to the PS I complex. Strain PR6309 (psaL−) was capable of performing a state 2 to state 1 transition approximately three times more rapidly than the wild type. Because the monomeric PS I complexes of this mutant should be capable of diffusing more rapidly than trimeric complexes, these data suggest that PS I complexes rather than phycobilisomes might move during state transitions. A “mobile‐PS I” model for state transitions that incorporat

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1996.tb02421.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractThis paper describes the results of a study of the photophysical properties of various methyl‐angelicins (MA) in solvents of different polarity and proticity. The behavior of their excited singlet and triplet states was investigated by fluorometry and nanosecond laser flash photolysis. On the basis of semiempirical (ZINDO/S‐CI) calculations and the solvent effect on the absorption and fluorescence properties, the lowest excited singlet state (S1) is assigned to a partially allowed π, π* state. The close lying S2state is n,π* in nature. The efficiency of the decay pathways of S1(fluorescence, intersystem crossing and internal conversion) strongly depends on the energy gap between the S1and S2states consistent with the manifestation of “proximity effect.” Thus, MA in cyclohexane decay only through S1→ S0internal conversion, while in acetonitrile and ethanol, where the n, π* state is located at higher energy, their fluorescence and intersystem crossing increase significantly. The lowest excited triplet states (T1) were characterized in terms of their absorption spectra, decay kinetics, molar absorption coefficients and formation quantum yields. The interaction of T1MA with molecular oxygen leads to an efficient formation of singlet oxygen, as evidenced by the appearance of characteristic IR phosphorescence center

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1996.tb02422.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY