Elementary Energy Transfer Pathways in Allochromatium vinosum Photosynthetic Membranes

Allochromatium vinosum (formerly Chromatium vinosum) purple bacteria are known to adapt their light-harvesting strategy during growth according to environmental factors such as temperature and average light intensity. Under low light illumination or low ambient temperature conditions, most of the LH2 complexes in the photosynthetic membranes form a B820 exciton with reduced spectral overlap with LH1. To elucidate the reason for this light and temperature adaptation of the LH2 electronic structure, we performed broadband femtosecond transient absorption spectroscopy as a function of excitation wavelength in A. vinosum membranes. A target analysis of the acquired data yielded individual rate constants for all relevant elementary energy transfer (ET) processes. We found that the ET dynamics in high-light-grown membranes was well described by a homogeneous model, with forward and backward rate constants independent of the pump wavelength. Thus, the overall B800→B850→B890→ Reaction Center ET cascade is well described by simple triexponential kinetics. In the low-light-grown membranes, we found that the elementary backward transfer rate constant from B890 to B820 was strongly reduced compared with the corresponding constant from B890 to B850 in high-light-grown samples. The ET dynamics of low-light-grown membranes was strongly dependent on the pump wavelength, clearly showing that the excitation memory is not lost throughout the exciton lifetime. The observed pump energy dependence of the forward and backward ET rate constants suggests exciton diffusion via B850→ B850 transfer steps, making the overall ET dynamics nonexponential. Our results show that disorder plays a crucial role in our understanding of low-light adaptation in A. vinosum.     

The role of chromophore coupling in tuning the spectral properties of peripheral light-harvesting protein of purple bacteria

The publication of a structure for the peripheral light-harvesting complex of a purple photosynthetic bacterium (McDermott et al. (1995), Nature 374: 517–521) provides a framework within which we can begin to understand various functional aspects of these complexes, in particular the relationship between the structure and the red-shift of the bacteriochlorophyll Q_y transition. In this article we describe calculations of some of the spectral properties expected for an array of chromophores with the observed geometry. We report the stability of the calculated absorption spectrum to minor structural alterations, and deduce that the observed red shift of the 850 nm Q_y transition in the B800–850 antenna complexes is about equally attributable to chromophore-chromophore and chromophore-protein interactions, while chromophore-chromophore interactions predominate in generating the red-shift of the 820 nm Q_y transition in B800–820 type peripheral liggt-harvesting complexes. Finally we suggest that the red shift in the absorbance of the monomeric Bchl a found in antenna complexes to 800 nm, from 770 nm as observed in most solvents, is largely attributable to a hydrogen bond with the 2-acetyl group of this chromophore.     

Reconstitution of carotenoids into the light-harvesting complex B800-850 of Chromatium minutissimum

Chromatophores and peripheral light-harvesting complexes B800–850 with a trace of carotenoids were isolated from Chromatium minutissimum cells in which carotenoid biosynthesis was inhibited by diphenylamine. Three methods previously used for the reconstitution of carotenoids into either the light-harvesting (LH1) type complexes or reaction centers (RC) of carotenoidless mutants were examined for the possibility of carotenoid reconstitution into the carotenoid depleted chromatophores. All these methods were found to be unsuitable because carotenoid depleted complex B800–850 from Chr. minutissimum is characterized by high lability. We have developed a novel method maintaining the native structure of the complexes and allowing reconstitution of up to 80% of the carotenoids as compared to the control. The reconstituted complex has a similar CD spectrum in the carotenoid region as the control, and its structure restores its stability. These data give direct proof for the structural role of carotenoids in bacterial photosynthesis.     

Effect of modification of histidine residues on organization of the pigment--protein complexes of chromatium minutissimum

The effect of diethyl pyrocarbonate on chromatophores and isolated pigment--protein complexes of Chromatium minutissimum was studied. It is shown that modification of histidine residues results in the destruction of the core antenna LHI (B880) and in a spectral shift from 850 to 830 nm in the peripheral antenna LHII (B800-850). In the purple sulfur bacterium Chromatium minutissimum the pigment--protein complexes B800-B850 (peripheral antenna, LHII) and B880 (core antenna, LHI) collect and transmit the absorbed light energy to the reaction centers. The composition of pigments and proteins as well as primary structure of the majority of polypeptides in both types of complexes from various photosynthetic bacteria have been determined.     

High pressure studies of energy transfer and strongly coupled bacteriochlorophyll dimers in photosynthetic protein complexes

High pressure is used with hole burning and absorption spectroscopies at low temperatures to study the pressure dependence of the B800B850 energy transfer rate in the LH2 complex of Rhodobacter sphaeroides and to assess the extent to which pressure can be used to identify and characterize states associated with strongly coupled chlorophyll molecules. Pressure tuning of the B800–B850 gap from 750 cm^\s-1 at 0.1 MPa to 900 cm^-1 at 680 MPa has no measurable effect on the 2 ps energy transfer rate of the B800–850 complex at 4.2 K. An explanation for this resilience against pressure, which is supported by earlier hole burning studies, is provided. It is based on weak coupling nonadiabatic transfer theory and takes into account the inhomogeneous width of the B800–B850 energy gap, the large homogeneous width of the B850 band from exciton level structure and the Franck-Condon factors of acceptor protein phonons and intramolecular BChl a modes. The model yields reasonable agreement with the 4.2 K energy transfer rate and is consistent with its weak temperature dependence. It is assumed that it is the C₉-ring exciton levels which lie within the B850 band that are the key acceptor levels, meaning that BChl a modes are essential to the energy transfer process. These ring exciton levels derive from the strongly allowed lowest energy component of the basic B850 dimer. However, the analysis of B850s linear pressure shift suggests that another Förster pathway may also be important. It is one that involves the ring exciton levels derived from the weakly allowed upper component of the B850 dimer which we estimate to be quasi-degenerate with B800. In the second part of the paper, which is concerned with strong BChl monomer-monomer interactions of dimers, we report that the pressure shifts of B875 (LH2), the primary donor absorption bands of bacterial RC (P870 of Rb. sphaeroides and P960 of Rhodopseudomonas viridis) and B1015 (LH complex of Rps. viridis) are equal and large in value (-0.4 cm⁰¹/MPa at 4.2 K) relative to those of isolated monomers in polymers and proteins (< -0.1 cm⁰¹/MPa). The shift rate for B850 at 4.2 K is-0.28 cm^–1/MPa. A model is presented which appears to be capable of providing a unified explanation for the pressure shifts.Abbreviations B800 BChl antenna band absorbing (at room temperature) at 800 nm (B850, B875, B1015 are defined similarly) - CD circular dichroism - FC factor Franck-Condon factor - FMO comple Fenna-Matthews-Olson complex - L-S theory Laird-Skinner theory - LH1 core light-harvesting complex of the BChl antenna complexes - LH2 peripheral light-harvesting complex of the BChl antenna complexes - NPHB non-photochemical hole burning - P960 absorption band of special pair of Rhodopseudomonas viridis absorbing at 960 nm (room temperature). P870 of Rhodobacter sphaeroides is defined similarly - QM/MM results quantum mechanical/molecular mechanical results - RC reaction center - ZPH zero phonon hole     

The complete amino acid sequence of the antenna polypeptide B806-866-β from the cytoplasmic membrane of the green bacterium Chloroflexus auranliacus

The bacteriochlorophyll a-binding polypeptide B806–866-β was extracted from membranes of the green thermophilic bacterium Chloroflexus aurantiacus with chloroform/methanol/ammonium acetate. Purification of the antenna polypeptide (6.3 kDa) was achieved by chromatography on Sephadex LH-60, Whatman DE-32 and by FPLC. The complete amino acid sequence (53 amino acid residues) was determined. The B806–866-β polypeptide is sequence homologous to the antenna β-polypeptides of purple bacteria (27–40%) and exhibits the characteristic three domain structure of the B870, B800–850 and B800–820 antenna complexes. The two typical His residues, conserved in all antenna β-polypeptides of purple bacteria, were found: His-24 lies within the N-terminal hydrophilic domain and His-42 within the central hydrophobic domain. This polypeptide together with the previously described α-polypeptide form the basic structural unit of the B806–866 antenna complex from C. aurantiacus.     

The effect of growth conditions on the light-harvesting apparatus in Rhodopseudomonas acidophila

The detailed effect on the light-harvesting apparatus of three different wild-type strains of Rhodopseudomonas acidophila in response to changes in both light-intensity and temperature have been investigated. In all three strains at high light-intensities (160 mol s m² and above) the only LH2 antenna complex synthesised is the B800–850 complex. In strains 7050 and 7750 as the light-intensity is lowered the B800–850 complex is gradually replaced by another type of LH2 the B800–820 complex. However, at no light-intensities studied is this changeover complete when the cells are grown at 30°C. If however, the light-intensity is lowered at temperatures below 25°C with strain 7750 there is a complete replacement of the B800–850 complex by the B800–820 complex. At all light-intensities and temperatures tested, strain 10050 only synthesised the B800–850 complex. Strain 7050 also responded to changes in light-intensity by altering its carotenoid composition. At high light-intensity the major carotenoids were rhodopin and rhodopin-glucoside, while at low light-intensities the major ones were rhodopinal and rhodopinal-glucoside. This change in carotenoid content started to occur at rather higher light-intensities than the switchover from B800–850 to B800–820.     

Search for polythionates in cultures of Chromatium vinosum after sulfide incubation

Cultures of Chromatium vinosum, devoid of sulfur globules, were supplemented with sulfide and incubated under anoxic conditions in the light. The concentrations of sulfide, polysulfides, thiosulfate, polythionates and elemental sulfur (sulfur rings) were monitored for 3 days by ion-chromatography and reversed-phase HPLC. While sulfide disappeared rapidly, thiosulfate and elemental sulfur (S₆, S₇ S₈ rings) were formed. After sulfide depletion, the concentration of thiosulfate decreased fairly rapidly, but elemental sulfur was oxidized very slowly to sulfate. Neither polysulfides (S _x ^2– ), polythionates (S_nO ₆ ^2– , n=4–6), nor other polysulfur compounds could be detected, which is in accordance with the fact that sulfide-grown cells were able to oxidize polysulfide without lag. The nature of the intracellular sulfur globules is discussed.     

Isolation and purification of membrane-bound cytochrome b-560 from photosynthetic bacterium Chromatium vinosum

A membrane-bound cytochrome of the b-type (cytochrome b-560) was success-fully purified from chromatophores of the photosynthetic purple sulfur bacterium Chromatium vinosum by treatment with sodium cholate, sodium deoxycholate, sodium thiocyanate, and bacterial alkaline protease (EC 3·4·21·14) followed by gel filtration.The purified cytochrome b-560 showed the absorption maxima at 279, 412.5 and 533 nm in the oxidized form, and 427, 530 and 560 nm in the reduced form. Reduced-minus-oxidized difference millimolar absorption coefficient was 14.0 for a wavelength pair, 560 minus 540 nm.Isolated cytochrome b-560 was electrophoretically homogeneous, and its minimal molecular weight was estimated to the 13,000 by SDS polyacrylamide gel electrophoresis.The midpoint potential at pH 8.0 was –110mV, and was not dependent on the ambient pH in the pH range of 6.8 to 8.8.     

酒色着色菌利用产酸克雷伯氏菌发酵废液产氢

研究了酒色着色菌(Chromatium vinosum DSM185)利用产酸克雷伯氏菌（Klebsiella oxytoca HP1）发酵产氢废液进行光发酵和暗发酵产氢的可行性,以达到对产氢底物的充分利用和对产氢废液的进一步处理。研究结果表明C.vinosum可以利用K.oxytoca的发酵废液进行光发酵产氢和暗发酵产氢。C.vinosum发酵产氢后废液中残余还原糖和主要有机酸（丁酸）的含量明显降低,发酵产氢的最佳pH为6.5,添加0.1%(W/W)NH₄Cl能促进产氢。在光照条件下丁酸利用率可达54.38%,产氢量达36.97 mL/mg;在黑暗条件下丁酸利用率可达36.01%,产氢量达37.50mL/mg。     

Characterisation of the LH2 spectral variants produced by the photosynthetic purple sulphur bacterium Allochromatium vinosum

This study systematically investigated the different types of LH2 produced by Allochromatium (Alc.) vinosum, a photosynthetic purple sulphur bacterium, in response to variations in growth conditions. Three different spectral forms of LH2 were isolated and purified, the B800-820, B800-840 and B800-850 LH2 types, all of which exhibit an unusual split 800 peak in their low temperature absorption spectra. However, it is likely that more forms are also present. Relatively more B800-820 and B800-840 are produced under low light conditions, while relatively more B800-850 is produced under high light conditions. Polypeptide compositions of the three different LH2 types were determined by a combination of HPLC and TOF/MS. The B800-820, B800-840 and B800-850 LH2 types all have a heterogeneous polypeptide composition, containing multiple types of both α and β polypeptides, and differ in their precise polypeptide composition. They all have a mixed carotenoid composition, containing carotenoids of the spirilloxanthin series. In all cases the most abundant carotenoid is rhodopin; however, there is a shift towards carotenoids with a higher conjugation number in LH2 complexes produced under low light conditions. CD spectroscopy, together with the polypeptide analysis, demonstrates that these Alc. vinosum LH2 complexes are more closely related to the LH2 complex from Phs. molischianum than they are to the LH2 complexes from Rps. acidophila.     

Buoyant density changes due to intracellular content of sulfur in Chromatium warmingii and Chromatium vinosum

Average specific density of individual cells of pure cultures of Chromatium warmingii and Chromatium vinosum were measured by isopicnic gradient centrifugation with Percoll during growth at constant illumination as a function of the increasing content of intracellular sulfur. Cell number and volume, bacteriochlorophyll a, sulfide, and sulfur were followed in the cultures along with cellular buoyant density. Poly--hydroxybutyrate was monitored at several points during growth of the cultures. The density of C. warmingii changed from 1.071 to 1.108 g cm^-3 (sulfur content per cell varied from 0 to 1.71pg). C. vinosum changed its density from 1.096 to 1.160 g cm^-3 (sulfur content per cell varied from 0 to 0.43 pg). Maximum sulfur content in pg of sulfur per m³ of cell volume were 0.178 for C. warmingii and 0.294 for C. vinosum. Measurement of the differences in buoyant density, volume and sulfur content before and after ethanol extraction of cells with and without intracellular sulfur, allowed tentatively to estimate the density of sulfur inside the cells as 1.219 g cm^-3. Isolation of sulfur globules and centrifugation in density gradients gave a density higher than 1.143 g cm^-3 for these intracellular inclusions.Non-common abbreviations Bchl Bacteriochlorophyll - DMB Density Marker Beads - PHB poly--hydroxybutyrate     

Isolation and characterization of sulfur globule proteins from Chromatium vinosum and Thiocapsa roseopersicina

Purple sulfur bacteria store sulfur as intracellular globules enclosed by a protein envelope. The proteins associated with sulfur globules of Chromatium vinosum and Thiocapsa roseopersicina were isolated by extraction into 50% aqueous acetonitrile containing 1% trifluoroacetic acid and 10 mM dithiothreitol. The extracted proteins were separated by reversed-phase HPLC, revealing three major proteins from C. vinosum and two from T. roseopersicina. All of these proteins have similar, rather unusual amino acid compositions, being rich in glycine and aromatic amino acids, particularly tyrosine. The molecular masses of the C. vinosum proteins were determined to be 10,498, 10,651, and 8,479 Da, while those from T. roseopersicina were found to be 10,661 and 8,759 Da by laser desorption time-of-flight mass spectrometry. The larger T. roseopersicina protein is N-terminally blocked, probably by acetylation, but small amounts of the unblocked form (mass = 10,619) were also isolated by HPLC. Protein sequencing showed that the two larger C. vinosum proteins are homologous to each other and to the large T. roseopersicina protein. The 8,479 Da C. vinosum and 8,759 Da T. roseopersicina proteins are also homologous, indicating that sulfur globule proteins are conserved between different species of purple sulfur bacteria.Abbreviations BNPS-skatole 2 (2-Nitrophenylsulfenyl)-3-methyl-3-bromoindolenine - CNB Cyanogen bromide - Cv1, Cv2, and Cv3 Chromatium vinosum sulfur globule proteins - SGP and SGPs Sulfur globule protein(s) - TFA Trifluoroacetic acid - Tr0, Tr1, and Tr2 Thiocapsa roseopersicina sulfur globule proteins     

Pigment organization and energy transfer in the green photosynthetic bacterium Chloroflexus aurantiacus

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 Q_y 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 Q_y 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     

Localization of ribulose-bisphosphate carboxylase-oxygenase and its putative binding protein in the cell envelope of Chromatium vinosum

Antibodies to the large and small subunits of ribulose-bisphosphate carboxylase-oxygenase (RuBisCO; EC 4.1-1.39) and a putative binding protein (PBP) for RuBisCO from Chromatium vinosum have been used to localize these proteins in thin sections. Immunogold techniques employing single and double antibodies establish that RuBisCO and the RuBisCO PBP are concentrated in the cell envelope of C. vinosum.Abbreviations kDa kilodalton - L large subunit of RuBisCO - PBP putative binding protein of RuBisCO - RuBisCO ribulose-bisphosphate carboxylase-oxygenase - S small subunit of RuBisCO To whom correspondence should be addressed.     

Temperature dependence of cytochrome photooxidation and conformational dynamics of Chromatium reaction center complexes

A temperature dependence of multiheme cytochrome c oxidation induced by a laser pulse was studied in photosynthetic reaction center preparations from Chromatium minutissimum. Absorbance changes and kinetic characteristics of the reaction were measured under redox conditions where one or all of the hemes of the cytochrome subunit are chemically reduced (E _h =+300 mV or E _h =–20 to -60 mV respectively). In the first case photooxidation is inhibited at temperatures lower than 190–200 K with the rate constant of the photooxidation reaction being practically independent on temperature over the range of 300 to 190 K (k=2.2×10⁵ s^-1). Under reductive conditions (E _h =–20 to -60 mV) lowering the temperature to 190–200 K causes the reaction to slow from k=8.3×10⁵ s^-1 to 2.1×10⁴ s^-1. Under further cooling down to the liquid nitrogen temperature, the reaction rate changes negligibly. The absorption amplitude decreases by 30–40% on lowering the temperature. A new physical mechanism of the observed critical effects of temperature on the rate and absorption amplitude of the multiheme cytochrome c oxidation reaction is proposed. The mechanism suggests a close interrelation between conformational mobility of the protein and elementary electron tunneling act. The effect of freezing conformational motion is described in terms of a local diffusion along a random rough potential.     

The enzymatic system thiosulfate: Cytochrome c oxidoreductase from photolithoautotrophically grown Chromatium vinosum

Chromatium vinosum cells form a vesicular type intracytoplasmic membrane system during phototrophic growth on thiosulfate.—An enzyme protein transferring electrons from thiosulfate to cytochromes of type c was enriched from S-144. The colorless thiosulfate: cytochrome c oxidoreductase was characterized by a molecular weight of 36,000 (after dodecylsulfate treatment) and 35,000 (by gel filtration). Isoelectric focusing revealed a pI range of 4.4 to 4.7. Apparent K _m values for the cytochromes tested were in the M range. — The endogenous electron acceptor compound, isolated from the chromatophore fraction P-144, was found to be a membrane-bound cytochrome c-552. The homogeneous cytochrome protein had an average pI value of 4.65 and a molecular weight of 71,500 determined by gel filtration. By dodecylsulfate electrophoresis it was cleaved into two proteins representing particle weights of 45,000 and 20,000.Abbreviations HiPIP high potential nonheme iron protein - IEF isoelectric focusing - SDS dodecylsulfate, sodium salt - Temed N,N,N,N-tetramethylethylenediamine     

Effect of illumination intensity and inhibition of carotenoid biosynthesis on assembly of peripheral light-harvesting complexes in purple sulfur bacteria <Emphasis Type="Italic">Allochromatium vinosum</Emphasis> ATCC 17899

Effect of illumination intensity and inhibition of carotenoid biosynthesis on assemblage of different spectral types of LH2 complexes in a purple sulfur bacterium Allochromatium (Alc.) vinosum ATCC 17899 was studied. Under illumination of 1200 and 500 lx, the complexes B800-850 and B800-840 and B800-820 were assembled. While rhodopine was the major carotenoid in all spectral types of the LH2 complex, a certain increase in the content of carotenoids with higher numbers of conjugated double bonds (anhydrorhodovibrin and didehydrorhodopin) was observed in the B800-820 complex. At 1200 lx, the cells grew slowly at diphenylamine (DPA) concentrations not exceeding 53 μM, while at illumination intensity decreased to 500 lx they could grow at 71 μM DPA (DPA cells). Independent on illumination level, the inhibitor is supposed to impair the functioning of phytoene synthetase (resulting in a decrease in the total carotenoid content) and of phytoene desaturase, which results in formation of neurosporene hydroxy derivatives and ζ-carotene. In the cells grown at 500 lx, small amounts of spheroidene and OH-spheroidene were detected. These carotenoids were originally found under conditions of carotenoid synthesis inhibition in bacteria with spirilloxanthin as the major carotenoid. Carotenoid content in the LH2 complexes isolated from the DPA cells was ~15% of the control (without inhibition) for the B800-850 and ~20% of the control for the B800-820 and B800-840 DPA complexes. Compared to the DPA pigment-containing membranes, the DPA complexes were enriched with carotenoids due to disintegration of some carotenoidless complexes in the course of isolation. These results support the supposition that some of the B800-820, B800-840, and B800-850 complexes may be assembled in the cells of Alc. vinosum ATCC 17899 without carotenoids. Comparison of the characteristics obtained for Alc. vinosum ATCC 17899 and the literature data on strain D of the same bacteria shows that they belong to two different strains, rather than to one as was previously supposed.     

A partial purification of membrane-bound b and c cytochromes from Chromatium vinosum.

Three membrane-bound cytochromes from the photosynthetic purple sulfur bacterium Chromatium vinosum have been partially separated from other membrane components by treatment with deoxycholate followed by ammonium sulfate fractionation and chromatography on Bio-Gel A1.5. Cytochrome c₅₅₅, present in relatively small amounts in the deoxycholate extract, has an α-band that splits into two bands at 548 and 552.5 nm at liquid nitrogen temperature. The major components of the deoxycholate extract are cytochromes c₅₅₃ and b₅₆₀, which are present in essentially equimolar amounts through all the stages of the purification procedure.     

Temperature Broadening of LH2 Absorption in Glycerol Solution

In order to determine the relationship between the pigment–protein and the pigment–pigment interactions, the measurements of absorption spectra of the peripheral light-harvesting complex LH2 from the purple bacteria Rhodobacter sphaeroides solvated in glycerol/buffer solution were carried out in a wide temperature range, from 4 to 250 K. The SDFs used for simulating the temperature dependence of B800 and B850 bands were determined in a parametric form. To fit experimental spectra the overall exciton–phonon coupling had to be assumed to be weak for B850 (λ/2V ≈ 0.3, where λ is the reorganization energy and V is the nearest-neighbor dipole–dipole coupling for bacteriochlorophylls). At physiological temperatures the intermediate nuclear bath dynamics compares with the magnitude of energy gap fluctuations. Slower dynamics with κ ≈ 0.39, where κ is the ratio of the nuclear relaxation rate and the line width parameter, determines the spectral shape of B850 whilst faster modulations characterize B800 (κ ≈2.39). The static disorder for the B800 band is relatively high with the characteristic value of the inhomogeneous bandwidth Γ^inh ≈120 cm⁻¹, while for the B850 band this value is almost equal to the dipole–dipole coupling strength (Γ^inh ≈360 cm⁻¹). It has been found that the LH2 absorption spectrum is likely to be influenced by the temperature dependence of the dielectric constant of the solution in the high temperature range, when the glycerol/buffer solution is in the liquid state.