4-Isobutyl homologs of farnesyl bacteriochlorophyll c in carbon tetrachloride

Absorption (ABS) and circular dichroism (CD) spectra were recorded for 3 concentrations (2.3, 19 and ca. 75 M) of 4-isobutyl homologs. Monomer spectra were the same as those for 4-n-propyl-5-ethyl farnesyl bacteriochlorophyll c. Pure polymer spectra were obtained by subtracting the 2.3-M spectra appropriately scaled from the ca. 75-M spectra. The polymer showed an ABS peak at 742 nm and a CD trough at ca. 742 nm. These properties are in harmony with the aggregate model proposed by Smith KM, Kehrs LA and Fajer J (1983, J Am Chem Soc 105: 1387–1389). A log-logplot of absorbance at 742 nm vs. monomer concentration could be fitted by a straight line of slope 1.6.Abbreviations ABS absorbance - BChl bacteriochlorophyll - CD circular dichroism - iBM/EF 4-isobutyl-5-methyl/ethyl farnesyl - PEF 4-n-propyl-5-ethyl farnesyl     

Aggregation of bacteriochlorophyll c homologs to dimers,tetramers, and polymers in water-saturated carbon tetrachloride

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     

Bacteriochlorophyll c monomers,dimers, and higher aggregates in dichloromethane,chloroform, and carbon tetrachloride

Bacteriochlorophyll c in vivo is a mixture of at least 5 homologs, all of which form aggregates in CH₂Cl₂, CHCl₃ and CCl₄. Three homologs exist mainly in the 2-R-(1-hydroxyethyl) configuration, whereas the other two homologs, 4-isobutyl-5-ethyl and 4-isobutyl-5-methyl farnesyl bacteriochlorophyll c, exist mainly in the 2-S-(1-hydroxyethyl) configuration (Smith KM, Craig GW, Kehres LA and Pfennig N (1983) J. Chromatograph. 281: 209–223). In CCl₄ the S-homologs form an aggregate of 2–3 molecules whose absorption (747 nm maximum) and circular dichroism spectra resemble those of the chlorosome. In CH₂Cl₂, CHCl₃ and CCl₄ the 4-n-propyl homolog (R-configuration) forms dimers absorbing at ca. 680 nm and higher aggregates absorbing at 705–710 nm. In CCl₄ the dimerization constant is approx. 10 µM^–1 (1000 times that for chlorophyll a). The difference between the types of aggregates formed by the 4-n-propyl and 4-isobutyl homologs is attributed to the difference between the R- and S-configurations of the 2-(1-hydroxyethyl) groups in each chlorophyll.Abbreviations BChl bacteriochlorophyll - CD circular dichroism - Chl chlorophyll - DNS data not shown - EEF 4-ethyl-5-ethyl farnesyl - iBM/EF 4-isobutyl-5-methyl/ethyl farnesyl - MEF 4-methyl-5-ethyl farnesyl - PEP 4-n-propyl-5-ethyl farnesyl     

Fluorescence lifetimes of dimers and higher oligomers of bacteriochlorophyll c from Chlorobium limicola

Fluorescence lifetimes have been measured for bacteriochlorophyll (BChl) c isolated from Chlorobium limicola in different states of aggregation in non-polar solvents. Two different homologs of BChl c were used, one with an isobutyl group at the 4 position, the other with n-propyl. Species previously identified as dimers (Olson and Pedersen 1990, Photosynth Res, this issue) decayed with lifetimes of 0.64 ns for the isobutyl homolog, 0.71 ns for n-propyl. Decay-associated spectra indicate that the absorption spectrum of the isobutyl dimer is slightly red-shifted from that of the n-propyl dimer. Aggregates absorbing maximally at 710 nm fluoresced with a principal lifetime of 3.1 ns, independent of the homolog used. In CCl₄, only the isobutyl homolog forms a 747-nm absorbing oligomer spectrally similar to BChl c in vivo. This oligomer shows non-exponential fluorescence decay with lifetimes of 67 and 19 ps. Because the two components show different excitation spectra, the higher oligomer is probably a mixture of more than one species, both of which absorb at 747 nm.Abbreviations BChl bacteriochlorophyll - Chl chlorophyll - % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGGipm0dc9vqaqpepu0xbbG8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeq4Xdm2aaW% baaSqabeaacaaIYaaaaaaa!3777!\[\chi ^2 \] chi-square - FWHM full-width at half-maximum     

Aggregation of 8,12-diethyl farnesyl bacteriochlorophyll c at low temperature

The effect of temperature on the aggregation of 3^lR-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     

Bacteriochlorophyll-c Homolog Composition in Green Sulfur Photosynthetic Bacterium Chlorobium vibrioformeDependent on the Concentration of Sodium Sulfide in Liquid Cultures

Green sulfur photosynthetic bacteria Chlorobium (Chl.) vibrioforme (DSM 263 strain and NCIB 8327 substrain possessing BChl-c) and Chl. tepidum (ATCC 49652) were photoautotrophically grown in liquid cultures containing different concentrations of sodium sulfide (Na₂S). BChl-c homologs possessing a methyl group at the 12-position tended to increase in cells of the two strains of Chl. vibrioforme cultured under high Na₂S concentrations. In contrast, the Na₂S concentration in liquid cultures did not affect the relative composition of BChl-c homologs in Chl. tepidum. 8-Propyl-12-methyl([P,M])-BChl-c homolog, which has been little observed in usual cultivations, could be isolated by reverse-phase high-performance liquid chromatography from the cells of Chl. vibrioforme grown under high Na₂S contents. The [P,M]-BChl-c homolog has the R-configuration at the 3¹-position, which was determined by ¹H-NMR analyses.     

A comparative study of the optical characteristics of intact cells of photosynthetic green sulfur bacteria containing bacteriochlorophyll c,d or e

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 Q_y 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     

The formation and characterization of the in vitro polymeric aggregates of bacteriochlorophyllc homologs fromChlorobium limicola in aqueous suspension in the presence of monogalactosyl diglyceride

Artificial aggregates of bacteriochlorophyllc (BChlc) were formed in an aqueous medium in the presence of a lipid, monogalactosyl diglyceride (MGDG), and the optical properties of those aggregates were studied by absorption and circular dichroism (CD) mainly. Four BChlc homologs, ([E,E]BChlc _F, [P,E]BChlc _F, [E,M]BChlc _F and [I,E]BChlc _F), were isolated from the green photosynthetic bacteriumChlorobium limicola strain 6230. Above 0.0004%, MGDG induced a red-shift of the absorption maxima of BChlc aggregates. At 0.003% MGDG BChlc aggregates showed absorption maxima in the range of 724 to 745 (±3) nm with a shift of 12 to 24 (±3) nm depending on the homolog species. Four kinds of BChlc-MGDG aggregates showed characteristic CD spectra. [E,M]BChlc _F gave rise to a CD spectrum similar to that of chlorosomes, while the other three gave spectra of opposite sign. These aggregates are sensitive to 1-hexanol treatment; in a saturating amount (0.85%) of 1-hexanol, all the homologs gave a monomer-like absorption spectrum peaking at 670nm. At an intermediate concentration (0.5%), [E,M]BChlc _F showed an enhanced CD intensity, as observed in native chlorosomes. Resonance Raman spectra of the monomer-like BChlc samples indicated that the keto vibrational band at ca. 1640 cm^–1 was considerably weakened by the 0.85% 1-hexanol treatment, however the 1680 cm^–1 band characteristic of a free keto group did not appear. These results indicate that the artificial aggregates formed by purified BChlc homologs and MGDG are good models for studying chlorosomes structure.     

Biosynthesis of chlorosome proteins is not inhibited in acetylene-treated cultures of Chlorobium vibrioforme

The composition, abundance and apparent molecular masses of chlorosome polypeptides from Chlorobium tepidum and Chlorobium vibrioforme 8327 were compared. The most abundant, low-molecular-mass chlorosome polypeptides of both strains had similar electrophoretic mobilities and abundances, but several of the larger proteins were different in both apparent mass and abundance. Polyclonal antisera raised against recombinant chlorosome proteins of Cb. tepidum recognized the homologous proteins in Cb. vibrioforme, and a one-to-one correspondence between the chlorosome proteins of the two species was confirmed. As previously shown [Ormerod et al. (1990) J Bacteriol 172: 1352–1360], acetylene strongly suppressed the synthesis of bacteriochlorophyll c in Cb. vibrioforme strain 8327. No correlation was found between the bacteriochlorophyll c content of cells and the cellular content of chlorosome proteins. Nine of ten chlorosome proteins were detected in acetylene-treated cultures, and the chlorosome proteins were generally present in similar amounts in control and acetylene-treated cells. These results suggest that the synthesis of chlorosome proteins and the assembly of the chlorosome envelope is constitutive. It remains possible that the synthesis of bacteriochlorophyll c and its insertion into chlorosomes might be regulated by environmental parameters such as light intensity.This revised version was published online in October 2005 with corrections to the Cover Date.     

Different Sensitivities to Oxygen Between Two Strains of the Photosynthetic Green Sulfur Bacterium Chlorobium vibrioforme NCIB 8327 with Bacteriochlorophyll c and d

Two sub-strains of the anoxygenic photosynthetic green sulfur bacterium Chlorobium vibrioforme NCIB 8327 were derived from the same clone and could be discriminated only by their possession of either bacteriochlorophyll (BChl) c or d as the major pigment in the peripheral light-harvesting antenna system, chlorosome (Saga Y et al. (2003) Anal Sci 19: 1575–1579). In the presence of a proper amount of oxygen in the initial culture medium, the BChl d strain showed longer retardation on its growth initiation than the BChl c strain, indicating that the latter was advantageous for survival under aerobic light conditions which produced reactive oxygen species in vivo. The result would be ascribable to the difference of the midpoint potentials between two kinds of chlorosomes formed by self-aggregates of BChl c and d as measured by their fluorescence quenching.     

Study of the chlorosomal antenna of the green mesophilic filamentous bacterium Oscillochloris trichoides

Whole cells, chlorosome-membrane complexes and isolated chlorosomes of the green mesophilic filamentous bacterium Oscillochloris trichoides, representing a new family of the green bacteria Oscillochloridaceae, were studied by optical spectroscopy and electron microscopy. It was shown that the main light-harvesting pigment in the chlorosome is BChl c. The presence of BChl a in chlorosomes was visualized only by pigment extraction and fluorescence spectroscopy at 77 K. The molar ratio BChl c: BChl a in chlorosomes was found to vary from 70:1 to 110:1 depending on light intensity used for cell growth. Micrographs of negatively and positively stained chlorosomes as well as of ultrathin sections of the cells were obtained and used for morphometric measurements of chlorosomes. Our results indicated that Osc. trichoides chlorosomes resemble, in part, those from Chlorobiaceae species, namely, in some spectral features of their absorption, fluorescence, CD spectra, pigment content as well as the morphometric characteristics. Additionally, it was shown that similar to Chlorobiaceae species, the light-harvesting chlorosome antenna of Osc. trichoides exhibited a highly redox-dependent BChl c fluorescence. At the same time, the membrane B805–860 BChl a antenna of Osc. trichoides is close to the membrane B808–866 BChl a antenna of Chloroflexaceae species. This revised version was published online in June 2006 with corrections to the Cover Date.     

Tubular exciton models for BChl c antennae in chlorosomes from green photosynthetic bacteria

Exciton calculations on tubular pigment aggregates similar to recently proposed models for BChl c/d/e antennae in light-harvesting chlorosomes from green photosynthetic bacteria yield electronic absorption spectra that are super-impositions of linear J-aggregate spectra. While the electronic spectroscopy of such antennae differs considerably from that of linear J-aggregates, tubular exciton models (which may be viewed as cross-coupled J-aggregates) may be constructed to yield spectra that resemble that of the BChl c antenna in the green bacterium Chloroflexus aurantiacus. Highly symmetric tubular models yield absorption spectra with dipole strength distributions essentially identical to that of a J-aggregate; strong symmetry-breaking is needed to simulate the absorption spectrum of the BChl c antenna.Abbreviations BChl bacteriochlorophyll - [E,M] BChl c _S bacteriochlorophyll c with ethyl and methyl substituents in the 8- and 12-positions, and with stearol as the esterifying alcohol     

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

The transfer of excitation energy and the pigment arrangement in isolated chlorosomes of the thermophilic green bacterium Chloroflexus aurantiacus were studied by means of absorption, fluorescence and linear dichroism spectroscopy, both at room temperature and at 4 K. The low temperature absorption spectrum shows bands of the main antenna pigments BChl c and carotenoid, in addition to which bands of BChl a are present at 798 and 613 nm. Fluorescence measurements showed that excitation energy from BChl c and carotenoid is transferred to BChl a, which presumably functions as an intermediate in energy transfer from the chlorosome to the cytoplasmic membrane. Measurements of fluorescence polarization and the use of two different orientation techniques for linear dichroism experiments enabled us to determine the orientation of several transition dipole moments with respect to each other and to the three principal axes of the chlorosome. The Q_y transition of BChl a is oriented almost perfectly perpendicular to the long axis of the chlorosome. The Q_y transition of BChl c and the -carotene transition dipole are almost parallel to each other. They make an angle of about 40° with the long axis and of about 70° with the short axis of the chlorosome; the angle between these transitions and the BChl a Q_y transition is close to the magic angle (55°).Abbreviations BChl bacteriochlorophyll - CD circular dichroism - LD linear dichroism Dedicated to Prof. L.N.M. Duysens on the occasion of his retirement.     

Generation and quenching of singlet molecular oxygen by aggregated bacteriochlorophyll d in model systems and chlorosomes

Both photogeneration and quenching of singlet oxygen by monomeric and aggregated (dimeric and oligomeric) molecules of bacteriochlorophyll (BChl) d have been studied in solution and in chlorosomes isolated from the green photosynthetic bacterium Chlorobium vibrioforme f. thiosulfatophilum. The yield of singlet-oxygen photogeneration by pigment dimers was about 6 times less than for monomers. Singlet oxygen formation was not observed in oligomer-containing solutions or in chlorosomes. To estimate the efficiency of singlet oxygen quenching an effective rate constant for ¹O₂ quenching by BChl molecules (k_q ^M) was determined using the Stern-Volmer equation and the total concentration of BChl d in the samples. In solutions containing only monomeric BChl, the k_q ^M values coincide with the real values for ¹O₂ quenching rate constants by BChl molecules. Aggregation weakly influenced the k_q ^M values in pigment solutions. In chlorosomes (which contain both BChl and carotenoids) the k_q ^M value was less than in solutions of BChl alone and much less than in acetone extracts from chlorosomes. Thus ¹O₂ quenching by BChl and carotenoids is much less efficient in chlorosomes than in solution and is likely caused primarily by BChl molecules which are close to the surface of the large chlorosome particles. The data allow a general conclusion that monomeric and dimeric chlorophyll molecules are the most likely sources of ¹O₂ formation in photosynthetic systems and excitation energy trapping by the long wavelength aggregates as well as ¹O₂ physical quenching by monomeric and aggregated chlorophyll can be considered as parts of the protective system against singlet oxygen formation.Abbreviations BChl bacteriochlorophyll - MBpd methyl bacteriopheophorbide - Chl chlorophyll - TPP meso-tetraphenylporphyrin - TPPS meso-tetra (p-sulfophenyl) porphyrin     

Pigment organization and energy transfer in the green photosynthetic bacterium Chloroflexus aurantiacus. III. Energy transfer in whole cells

The transfer of excitation energy in intact cells of the thermophilic green photosynthetic bacterium Chloroflexus aurantiacus was studied both at low temperature and under more physiological conditions. Analysis of excitation spectra measured at 4K indicates that the minor fraction of bacteriochlorophyll a present in the chlorosome functions as an intermediate in energy transfer between the main light-harvesting pigment BChl c and the membrane-bound B808-866 antenna complex. This supports the hypothesis that BChl a is associated with the base plate which connects the chlorosome with the membrane. The overall efficiency for energy transfer from the chlorosome to the membrane is only 15% at 4K. High efficiencies of close to 100% are observed above 40°C near the temperature where the cultures are grown. Cooling to 20°C resulted in a sudden drop of the transfer efficiency which appeared to originate in the chlorosome. This decrease may be related to a lipid phase transition. Further cooling mainly affected the efficiency of transfer between the chlorosome and the membrane. This effect can only partially be explained by a decreased Förster overlap between the chlorosomal BChl a and BChl a 808 associated with the membrane-bound antenna system. The temperature dependence of the fluorescence yield of BChl a 866 also appeared to be affected by lipid phase transitions, suggesting that this fluorescence can be used as a native probe of the physical state of the membrane.     

Exciton interactions in dimers of bacteriochlorophyll and related molecules

Formalisms are developed for calculating the absorption wavelengths, dipole strengths and rotational strengths for dimers of bacteriochlorophyll and related molecules. The expressions explicitly consider the mixing of bacteriochlorophyll's four main excited states (Q_y, Q_x, B_x and B_y) in the ground and excited states of the dimer. This mixing must be considered in order to account for the hyperchromism and nonconservative circular dichroism found experimentally in oligomers of bacteriochlorophyll and bacteriopheophytin. The spectroscopic properties of the eight absorption bands of a bacteriopheophytin dimer are calculated as functions of the geometry of the dimer. The importance of the mixing of nondegenerate excited states, and of the mixing of doubly-excited states into the dimer's ground state, is evaluated by comparisons with calculations in which these phenomena are neglected. Structures for bacteriopheophytin dimers are found for which most of the calculated spectroscopic properties are consistent with the properties seen experimentally. Possible explanations are considered for the remaining discrepancies between the calculated and observed properties.     

Hole burning study of excited state structure and energy transfer dynamics of bacteriochlorophyll c in chlorosomes of green sulphur photosynthetic bacteria

Results of low temperature fluorescence and spectral hole burning experiments with whole cells and isolated chlorosomes of the green sulfur bacterium Chlorobium limicola containing BChl c are reported. At least two spectral forms of BChl c (short-wavelength and long-wavelength absorbing BChl c) were identified in the second derivative fluorescence spectra. The widths of persistent holes burned in the fluorescence spectrum of BChl c are determined by excited state lifetimes due to fast energy transfer. Different excited state lifetimes for both BChl c forms were observed. A site distribution function of the lowest excited state of chlorosomal BChl c was revealed. The excited state lifetimes are strongly influenced by redox conditions of the solution. At anaerobic conditions the lifetime of 5.3 ps corresponds to the rate of energy transfer between BChl c clusters. This time shortens to 2.6 ps at aerobic conditions. The shortening may be caused by introducing a quencher. Spectral bands observed in the fluorescence of isolated chlorosomes were attributed to monomeric and lower state aggregates of BChl c. These forms are not functionally connected with the chlorosome.Abbreviations BChl bacteriochlorophyll - EET electronic energy transfer - FWHM full width at half maximum - SDF site distribution function - RC reaction centre     

Identification of the major chlorosomal bacteriochlorophylls of the green sulfur bacteria Chlorobium vibrioforme and Chlorobium phaeovibrioides; their function in lateral energy transfer

The chlorosomal bacteriochlorophyll (BChl) composition of the green sulfur bacteria Chlorobium vibrioforme and Chlorobium phaeovibrioides was investigated by means of normal-phase high-performance liquid chromatography. From both species a number of homologues was isolated, which were identified by absorption and ²⁵²Cf-plasma desorption mass spectroscopy. Besides BChl d, C. vibrioforme contained a significant amount of BChl c, which may provide an explanation for the previous observation of at least two spectrally different pools of BChl in the chlorosomes of green sulfur bacteria (Otte et al. 1991). C. phaeovibrioides contained various homologues of BChl e only. Absorption spectra in acetone of BChl c, d and e, as well as bacteriopheophytin e are presented. No systematic differences were found for the various homologues of each pigment. In addition to farnesol, the mass spectra revealed the presence of various minor esterifying alcohols in both species, including phytol, oleol, cetol and 4-undecyl-2-furanmethanol, as well as an alcohol of low molecular mass, which is tentatively assumed to be decenol.Abbreviations BChl bacteriochlorophyll - BPh bacteriopheophytin (used as a general name for the Mg-free compound, irrespective of the esterifying alcohol) - HPLC high-performance liquid chromatography     

The molar extinction coefficient of bacteriochlorophyll e and the pigment stoichiometry in Chlorobium phaeobacteroides

We have determined the molar extinction coefficient of bacteriochlorophyll (BChl) e, the main light-harvesting pigment from brown-coloured photosynthetic sulfur bacteria. The extinction coefficient was determined using pure [Pr,E]BChl e_F isolated by reversed-phase HPLC from crude pigment extracts of Chlorobium (Chl.) phaeobacteroides strain CL1401. The extinction coefficients at the Soret and Q_y bands were determined in four organic solvents. The extinction coefficient of BChl e differs from those of other related Chlorobium chlorophylls (BChl c and BChl d) but is similar to that of chlorophyll b. The determined extinction coefficient was used to calculate the stoichiometric BChl e to BChl a and BChl e to carotenoids ratios in whole cells and isolated chlorosomes from Chl. phaeobacteroides strain CL1401 using the spectrum-reconstruction method (SRCM) described by Naqvi et al. (1997) (Spectrochim Acta A Mol Biomol Spectrosc 53: 2229–2234) . In isolated chlorosomes, BChl a content was ca. 1% of the total BChl content and the stoichiometric ratio of BChl e to carotenoids was 6. In whole cells, however, BChl a content was 3–4%, owing to the presence of BChl a-containing elements, i.e. FMO protein and reaction centre. An average of 5 BChl e molecules per carotenoid was determined in whole cells.     

Identification of the bacteriochlorophyll homologues of Chlorobium phaeobacteroides strain UdG6053 grown at low light intensity

Detailed APCI LC-MS/MS analysis using an improved HPLC separation reveals the green sulphur bacterium Chlorobium phaeobacteroides strain UdG6053 to contain a wider range of distinct bacteriochlorophyll homologues than has been previously recognised in Chlorobiaceae. The diversity in the homologue distribution is confirmed as arising from differences in the extent of alkylation of the macrocycle and variation in the nature of the esterifying alcohol and a novel series of bacteriochlorophyll structures has been recognised. Homologues containing esterifying alcohols other than farnesol, a number of which have not previously been reported in Chlorobiaceae, are present in high relative abundance. Confirmation of the structures of the esterifying alcohols has been obtained by hydrolysis and analysis by GC-MS. This revised version was published online in August 2006 with corrections to the Cover Date.