THE MULTIPLE PIGMENT-PROTEINS OF THE PHOTOSYSTEM I ANTENNA*

A photosystem I (PS I) holocomplex was obtained from barley by ultracentrifugation of PS I-enriched stroma lamellae on sucrose gradients. Further solubilization with glycosidic surfactants followed by Deriphat-poly-acrylamide gel electrophoresis (PAGE) fractionated the holocomplex into its core complex (CC I) and individual light-harvesting I (LHC I) pigment-protein subcomplexes. The LHC I contains chlorophyll a, all of the chlorophyll A of PS I and xanthophylls but no carotenes. Sodium dodecylsulfate PAGE analysis of the subcomplexes shows that barley LHC I is composed of at least five apoproteins having sizes between 11 and 24 kDa. Isolation of a 17 kDa LHC Ic component by Deriphat-PAGE shows it to be a photosynthetic pigment-protein. Room-temperature absorption spectra indicate that LHC Ic is enriched in chlorophyll a in comparison to the LHC Ia and Ib components. The LHC Ic apoprotein is shown to be distinct from the subunit III and IV polypeptides of CC I. Analysis of PS I fractions obtained from sucrose gradients as well as from Deriphat-PAGE indicates that in higher plants an oligomeric structure of the PS I entity exists in vitro.     

NONLINEAR LASERSPECTROSCOPIC INVESTIGATIONS OF THE PIGMENT-PIGMENT INTERACTION WITHIN THE LIGHT-HARVESTING COMPLEX OF PHOTOSYSTEM II

Using a pump and test beam technique in the frequency domain with pump pulses in the nanosecond time range, the nonlinear transmission properties were investigated at room temperature in photosystem (PS) II membrane fragments and isolated light-harvesting chlorophyll a/b-protein preparations (LHC II preparations). In LHC II preparations and PS II membrane fragments, respectively, pump pulses of 620 nm and 647 nm cause a transmission decrease limited to a wavelength region in the nearest vicinity of the pump pulse wavelength (full width at half maximum ' 0.24 nm). In contrast, at 670 nm neither a transmission decrease nor a narrow band feature were observed. The data obtained for PS II membrane fragments and LHC II preparations at shorter wavelengths (620 nm, 647 nm) were interpreted in terms of excited state absorption of whole pigment-protein clusters within the light-harvesting antenna of photosystem II. The interpretation of the small transmission changes as homogeneously broadened lines led to a transversal relaxation time for chlorophyll in the clusters of about 4 ps.     

THE LIGHT-HARVESTING SYSTEM OF THE UNICELLULAR ALGA Mantoniella squamata (PRASINOPHYCEAE): EVIDENCE FOR THE LACK OF A PHOTOSYSTEM I-SPECIFIC ANTENNA COMPLEX

The light-harvesting complexes (LHC) were isolated from the unicellular alga Mantoniella squamata (Prasinophyceae) by sucrose-density centrifugation. Beside the major LHC (II), a photosystem I complex was obtained that could be dissociated into a photosystem I core complex and an associated LHC I. In contrast to other chlorophyll b-containing antennae, both LHC II as well as LHC I were observed to be identical with respect to the following features: the molecular weights, the isoelectric points and the retention behavior on anion-exchange chromatography of the apoproteins, the pigment content and the absorption and fluorescence spectra. We conclude from these results that Mantoniella contains only one homogenous population of LHC, which cooperate with both photosystems not on the basis of specific recognition but on the simple basis of statistical interaction. This is the first report of a chlorophyll b-containing light-harvesting system without any subpopulations: therefore, it is suggested that it arises from a most primitive type of chlorophyll b-containing chloroplast.     

STRUCTURAL RELATIONSHIPS OF THE PHOTOSYSTEM I AND PHOTOSYSTEM II CHLOROPHYLL a/b AND a/c LIGHT-HARVESTING APOPROTEINS OF PLANTS AND ALGAE

Polyclonal antibodies against four different apoproteins of either the chlorophyll (Chl) a/b light-harvesting antenna of photosystem I or II, or a chlorophyll-protein complex homologous to CP26 from Chlamydomonas reinhardtii, crossreact with11–13 thylakoid proteins of Chlamydomonas, Euglena gracilis and higher plants. The number of antigenically-related proteins correlates with the quantity of light-harvesting chlorophyll-protein complex (LHC) gene types that have been sequenced in higher plants. The antibodies also react specifically with Chi a/c-binding proteins of three diatoms and Coccolithophora sp. as determined by immunoblot and Ouchterlony assays. Four to six crossreacting proteins are observed in each chromophyte species and a functional role for some can be deduced by antibody reactivity. It appears that despite major differences in the structures of their pigment ligands, at least some domains of Chl-binding LHC apoproteins have been conserved during their evolution, possibly functioning in protein: protein, as opposed to pigment: protein, interactions in photosynthetic membranes.     

Quenching of chlorophyll a singlets and triplets by carotenoids in light-harvesting complex of photosystem II: comparison of aggregates with trimers

Laser-induced changes in the absorption spectra of isolated light-harvesting chlorophyll a/b complex (LHC II) associated with photosystem II of higher plants have been recorded under anaerobic conditions and at ambient temperature by using multichannel detection with sub-microsecond time resolution. Difference spectra (ΔA) of LHC II aggregates have been found to differ from the corresponding spectra of trimers on two counts: (i) in the aggregates, the carotenoid (Car) triplet–triplet absorption band (ΔA>0) is red-shifted and broader; and (ii) the features attributable to the perturbation of the Q_y band of a chlorophyll a (Chla) by a nearby Car triplet are more pronounced, than in trimers. Aggregation, which is known to be accompanied by a reduction in the fluorescence yield of Chla, is shown to cause a parallel decline in the triplet formation yield of Chla; on the other hand, the efficiency (100%) of Chla-to-Car transfer of triplet energy and the lifetime (9.3 μs) of Car triplets are not affected by aggregation. These findings are rationalized by postulating that the antenna Cars transact, besides light-harvesting and photoprotection, a third process: energy dissipation within the antenna. The suggestion is advanced that luteins, which are buried inside the LHC II monomers, as well as the other, peripheral, xanthophylls (neoxanthin and violaxanthin) quench the excited singlet state of Chla by catalyzing internal conversion, a decay channel that competes with fluorescence and intersystem crossing; support for this explanation is presented by recalling reports of similar behaviour in bichromophoric model compounds in which one moiety is a Car and the other a porphyrin or a pyropheophorbide.     

Aggregation of the Light-Harvesting Complex in Intact Leaves of Tobacco Plants Stressed by CO2 Deficit

Pronounced aggregation of the photosystem II light-harvesting complex (LHC II) was observed in low-lightgrown tobacco plants stressed with a strong CO₂ deficit for 2–3 days. The LHC II aggregates showed a typical band at 697–700 nm (F₆₉₉) in low-temperature emission spectra. Its excitation spectrum corresponded to that of detergent-solubilized LHC II. Formation of F₆₉₉ in stressed plants was not reversed in the dark and leaves did not contain any zeaxanthin showing that neither a light-induced transthylakoid pH gradient nor zeaxanthin was required for LHC II aggregation. The CO₂-stressed plants showed clear signs of photodamage: depression of the potential yield of photosystem II photochemistry (F,/F_M) by 50–70% and a decline in chlorophyll content by 10–15%. Therefore, we propose that the photodamage to the photosynthetic apparatus is the cause of the LHC II aggregation in plants. The F₆₉₉ exhibited a reversible decrease of its intensity upon irradiation of leaves with intensive light. There was no or only slight decrease around 700 nm in unstressed plants. The nonphotochemical quenching of chlorophyll fluorescence showed the opposite relation, being higher before than after the strong CO₂ deficit. This discrepancy was likely related to the different LHC II aggregation state in control and stressed plants.     

Characterization of Two Light-Harvesting Subunits Isolated from the Brown Alga Pelvetia canaliculata: Heterogeneity of Xanthophyll Distribution

The main light-harvesting fraction from Pelvetia canaliculata was isolated on a sucrose density gradient from digitonin-solubilized chloroplasts. After further solubilization by dodecyl maltoside, the bulk fraction was separated into two subunits by preparative isoelectric focusing. The more acidic brown fraction was mainly composed of 22 kDa polypeptides having an apparent pI of 4.55. Its pigment composition was very simple, containing chlorophyll (Chi) a, Chi c and fucoxanthin. The in vivo spectral properties of fucoxanthin, namely a shift in light absorption to the green and efficient energy transmission to Chi a, were conserved in this subunit. No xanthophyll associated with photoprotection was found in this band, even when obtained from photoinhibited thalli. The less acidic green band contained predominantly 22 kDa polypeptides that were resolved into numerous components by denaturing isoelectric focusing. Its pigment composition was more complex, containing, in addition, pigments of the so-called xanthophyll cycle. In photoinhibited thalli, about half of the violaxanthin was converted into antheraxanthin and zeaxanthin. All the pigments of the xanthophyll cycle were specifically associated with this subunit, and it may thus have a central role in the thermal dissipation of the absorbed light energy as postulated for light-harvesting complex II isolated from green plants.     

NEAR-INFRARED-FT-RAMAN STUDY OF AGGREGATION OF BACTERIOCHLOROPHYLL c IN WHOLE LIVING Chlorobium limicola

Near-infrared excited Fourier-transform Raman spectra have been measured for whole living Chlorobium limicola f. thiosulfatophilum to explore in situ structure of bacteriochlorophyll c (BChl-c). The spectra, whose Raman bands are preresonance enhanced via a Qy band of BChl-c, did not contain contributions from the major components of bacteria such as proteins and lipids. Therefore, the spectra provide selective structural information about BChl-c in the chlorosomes in a totally nondestructive manner. A marker band, appearing at 1605 cm-1 for the coordination number of the Mg atom, shows that BChl-c in the chlorosomes is five coordinate. The Raman spectrum of living bacteria closely resembles that of BChl-c in water-saturated carbon tetrachloride (w-std CC14) where it is comprised of dimer, tetramer and polymer spectra. However, a band assigned to a C=O stretching mode of the 131-keto group is identified only at 1641 cm-1. A band arising from the free keto carbonyl group, which appears in the spectrum of BChl-c in w-std CC14, is not observed in the spectra of bacteria. These observations suggest that BChl-c in the chlorosomes forms mostly coordinate polymeric species whose structure is very similar to that of BChl-c in w-std CC14.     

Absorption and Fluorescence Spectral Database of Chlorophylls and Analogues

Absorption spectra and fluorescence spectra are essential for use across the photosciences, yet such spectra along with the all‐important values for molar absorption coefficient (ε) and fluorescence quantum yield (Φ_f) often are found with great difficulty. Here, a literature survey concerning the vital class of chlorophyll compounds has led to identification of spectra for 150 members. Spectra in print form have been digitized (with baseline corrections) and assembled into a database along with literature references, solvent identity and values for ε and Φ_f (where available). The database encompasses photosynthetic tetrapyrroles wherein the chromophore is a porphyrin (e.g. chlorophyll c₁, protochlorophyll a), chlorin (e.g. chlorophyll a, bacteriochlorophyll c) or bacteriochlorin (e.g. bacteriochlorophyll a). Altogether, the database contains 305 absorption spectra (from 19 porphyrins, 109 chlorins and 22 bacteriochlorins) and 72 fluorescence spectra (from 10 porphyrins, 30 chlorins and 4 bacteriochlorins). The spectral database should facilitate comparisons and quantitative calculations. All spectra are available in print form in the Supporting Information. The entire database in digital form is available with the PhotochemCAD program for free downloading and further use at http://www.photochemcad.com .     

EVENTS SURROUNDING THE EARLY DEVELOPMENT OF EUGLENA CHLOROPLASTS. 12. SPECTROSCOPIC EXAMINATION OF THE PROTOCHLOROPHYLL(IDE) PHOTOTRANSFORMATION IN INTACT CELLS*

Abstract— Absorption measurements in the 600–720 nm region of dark-grown cells of Euglena gracilis Klebs var. bacillaris Cori were made in vivo at room temperature using computer-assisted spectrophotometry. Dark-grown wild-type cells have a prominent absorption maximum at 634 nm due to protochlorophyll(ide) absorption. Upon illumination, the absorption at 634nm decreases and a peak appears at 674nm, representing the phototransformation of protochlorophyll(ide) to chlorophyll(ide). Using difference spectroscopy, the resynthesis in the dark of protochlorophyll(ide) by previously-illuminated wild-type dark-grown cells was found to begin at about 10min after illumination and reached completion by about 25 min, the amount of protochlorophyll(ide) resynthesized being equivalent to that of dark-grown cells. Resynthesis of protochlorophyll(ide) following a second illumination follows the same kinetics, indicating that protochlorophyll(ide) resynthesis is under tight regulation, possibly via feedback control. Cells of dark-grown wild-type and W₃BUL, a mutant lacking protochlorophyll(ide) contain a component absorbing at 658 nm which does not undergo phototransformation when examined by difference spectroscopy at room and liquid N₂ temperatures. Following the phototransformation of protochlorophyll(ide) 634 to chlorophyll(ide) 674, the chlorophyll(ide) 674 shifts to shorter wavelengths, ultimately to 671 nm. Possible relationships among the various spectroscopic forms of protochlorophyll(ide) and chlorophyll(ide) at room temperature and liquid N₂ temperature in Euglena and higher plants are presented. It is concluded that Euglena, unlike older, etiolated higher plants, contains only protochlorophyll(ide) 634, making it an excellent system in which to examine the phototransformation of this pigment species in the absence of other forms.     

ENERGY TRANSFER FROM PHYCOBILINS TO CHLOROPHYLL a IN HEAT-STRESSED CELLS OF Anacystis nidulans: CHARACTERIZATION OF THE LOW TEMPERATURE 683 nm FLUORESCENCE EMISSION BAND*

Abstract— Heat-induced changes of the characteristics of fluorescence spectra of Anacystis nidulans cells were studied after 39°C-grown cells were heated at 55°C. Heat-treatment of the cells induced no changes in the absorption properties or photosystem I-catalyzed cytochrome oxidation, but induced a dramatic change in the fluorescence characteristics of the cells. The low temperature fluorescence emission spectra of heated cells showed a large increase of fluorescence emission at683–685 nm (F683) and at 695 nm, while the bands at 660 nm (allophycocyanin) and at 718 nm (chlorophyll a of photosystem I) were not affected when the cells were excited with light absorbed by phycobilins. When the cells were heated for various periods, a progressive increase of the intensity of F683 occurred with the loss in oxygen evolution capacity. The increase of the F683 band was observed prior to the increase of the F695 band. Quenching of emission spectra by the addition of quinones indicates that the F683 band emanated mainly from a long wavelength form of allophycocyanin. Excitation spectra of heated cells measured at 77 K showed that light absorbed by phycobilins was effective in exciting F685, F695, and F715 emission. A possible energy distribution pathway in Anacystis nidulans is discussed.     

SPECTRAL FORMS AND ORIENTATION OF BACTERIOCHLOROPHYLLS c AND α IN CHLOROSOMES OF THE GREEN PHOTOSYNTHETIC BACTERIUM Chloroflexus aurantiacus

Spectral 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 (A_I? A₁)/(A_I+ A₁) of Bchl c and a measured 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 Bchl c with 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 Q_y transition 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 Q_y transition moment of the baseplate Bchl a peak 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 Bchl c was supported by the deconvolution of CD spectra and absorption spectra.     

ON THE EMERSON ENHANCEMENT EFFECT IN THE FERRICYANIDE HILL REACTION IN CHLOROPLAST FRAGMENTS*

Abstract— The Emerson effect is demonstrated in the ferricyanide Hill reaction when the rates of steady-state oxygen evolution are measured in spinach chlorplast fragments exposed to red (650 nm) and far-red (700 nm) light of high but not saturating intensity. However, at very low light intensity, the Emerson effect could not be observed. These experiments suggest that ferricyanide can be reduced at two sites. At low light intensity, the rate at one site predominates and at this site one photochemical system is active. At high light intensity, however, the action at a site that is dependent on the cooperation of two photochemical systems predominates. The action spectra of the ferricyanide Hill reaction measured in the presence of an excess of 650 nm or in the excess of 700 nm light show two peaks: one at 650 nm due to chlorophyll b and the other around 675 nm due to chlorophyll a. The ratio of chlorophyll a to chlorophyll b peaks is about 1.4 when 650 nm background light is used; the same ratio is about 0.7 with 700 nm background light. The two pigment systems seem to contain both chlorophyll a and chlorophyll b but in different proportions.     

Enhancement of Light Absorption Ability of Synthetic Chlorophyll Derivatives by Conjugation with a Difluoroboron Diketonate Group

The enhancement of the light absorption ability of synthetic chlorophyll derivatives is demonstrated. Chlorophyll derivatives directly conjugated with a difluoroboron 1,3‐diketonate group at the C3 position were synthesized from methyl pyropheophorbide‐d through Barbier acylmethylation of the C3‐formyl moiety, oxidation of the C3‐carbinol, and difluoroboron complexation of the diketonate. Electronic absorption spectra in a diluted solution showed that the synthetic conjugates gave an absorption band at λ=400–500 nm, with a Qy band shifted to a longer wavelength of λ≈700 nm. DFT calculations demonstrated that the absorption bands and redshifts were ascribable to the coupling of the LUMO of chlorin with that of the difluoroboron diketonate moiety. The introduction of a pyrenyl group at the C3³‐position of the conjugate afforded an additional charge‐transfer band over λ=500 nm, producing a pigment that bridged the green gap in standard chlorophylls.     

Photophysical Characterization of the Naturally Occurring Dioxobacteriochlorin Tolyporphin A and Synthetic Oxobacteriochlorin Analogues

Tolyporphins are tetrapyrrole macrocycles produced by a cyanobacterium‐containing culture known as HT‐58‐2. Tolyporphins A–J are free base dioxobacteriochlorins, whereas tolyporphin K is an oxochlorin. Here, the photophysical characterization is reported of tolyporphin A and two synthetic analogues, an oxobacteriochlorin and a dioxobacteriochlorin. The characterization (in toluene, diethyl ether, ethyl acetate, dichloromethane, 1‐pentanol, 2‐butanone, ethanol, methanol, N,N‐dimethylformamide and dimethylsulfoxide) includes static absorption and fluorescence spectra, fluorescence quantum yields and time‐resolved data. The data afford the lifetime of the lowest singlet excited state and the yields of the nonradiative decay pathways (intersystem crossing and internal conversion). The three macrocycles exhibit only modest variation in spectroscopic and excited‐state photophysical parameters across the solvents. The long‐wavelength (Q_y) absorption band of tolyporphin A appears at ~680 nm and is remarkably narrow (full‐width‐at‐half‐maximum ~7 nm). The position of the long‐wavelength (Q_y) absorption band of tolyporphin A (~680 nm) more closely resembles that of chlorophyll a (662 nm) than bacteriochlorophyll a (772 nm). The absorption spectra of tolyporphins B–I, K (which were available in minute quantities) are also reported in methanol; the spectra of B–I closely resemble that of tolyporphin A. Taken together, tolyporphin A generally exhibits spectral and photophysical features resembling those of chlorophyll a.     

AQUEOUS AGGREGATES OF BACTERIOCHLOROPHYLL c AS A MODEL FOR PIGMENT ORGANIZATION IN CHLOROSOMES

Chlorosomes isolated from Chloroflexus aurantiacus were extracted with chloroform/methanol. The extract contained bacteriochlorophylls c and a and 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 bacteriochlorophyll c at 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 bacteriochlorophyll c in both systems. Steady-state fluorescence studies showed that in the aggregate energy-transfer from bacteriochlorophyll c to a component emitting at 830 nm took place. When the aggregate was suspended in buffer saturated with 1-hexanol the 740 nm form of bacteriochlorophyll c was 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 dichroism signal.     

LIQUID-CRYSTALLINE PHASE TRANSITION OF MONOMOLECULAR LAYERS OF CHLOROPHYLL a*

Monomolecular layers of chlorophyll a at the air-water interface were investigated by absorption spectroscopy and simultaneous thermodynamic measurements. Whereas at temperatures near 20°C at all pressures, only a liquid phase exists, at a temperature of 4°C, a liquid-crystalline phase transition is observed at a surface pressure of 5 dynes/cm. Pressure-induced changes in the chlorophyll arrangement become evident from a drastic change in the absorption spectra, accompanying the phase transition. The crystalline phase exhibits an extremely narrow absorption band (halfwidth below 9 nm) centered at 698 nm, indicative of a coplanar chlorophyll arrangement in a well-ordered environment. It is highly probable that in these model membranes a chlorophyll arrrangement could be established that is equivalent to the one proposed for the reaction center P700.     

A Novel Route to 1‐Substituted 3‐(Dialkylamino)‐9‐oxo‐9H‐indeno[2,1‐c]pyridine‐4‐carbonitriles

Heptalenecarbaldehydes 1 / 1′ as well as aromatic aldehydes react with 3‐(dicyanomethylidene)‐indan‐1‐one in boiling EtOH and in the presence of secondary amines to yield 3‐(dialkylamino)‐1,2‐dihydro‐9‐oxo‐9H‐indeno[2,1‐c]pyridine‐4‐carbonitriles (Schemes 2 and 4, and Fig. 1). The 1,2‐dihydro forms can be dehydrogenated easily with KMnO₄ in acetone at 0° (Scheme 3) or chloranil (=2,3,5,6‐tetrachlorocyclohexa‐2,5‐diene‐1,4‐dione) in a ‘one‐pot’ reaction in dioxane at ambient temperature (Table 1). The structures of the indeno[2,1‐c]pyridine‐4‐carbonitriles 5′ and 6a have been verified by X‐ray crystal‐structure analyses (Fig. 2 and 4). The inherent merocyanine system of the dihydro forms results in a broad absorption band in the range of 515–530 nm in their UV/VIS spectra (Table 2 and Fig. 3). The dehydrogenated compounds 5, 5′ , and 7a – 7f exhibit their longest‐wavelength absorption maximum at ca. 380 nm (Table 2). In contrast to 5 and 5′, 7a – 7f in solution exhibit a blue‐green fluorescence with emission bands at around 460 and 480 nm (Table 4 and Fig. 5).     

ASSOCIATION OF CHLOROPHYLL WITH AMIDES ON PLASTICIZED POLYETHYLENE PARTICLES—I. N,N-DIMETH YLM YRISTAMIDE*

Abstract— Model systems have been prepared in which chlorophyll a (Chl a) and N.N-dimethylmyristamide (DMMA) are adsorbed together in various ratios to particles of polyethylene swollen with undecane. The adsorption is performed by equilibrating the particles with methanol-water solutions of increasing water content. Absorption spectra of the coated particles in viscous suspenions show sharp well-marked bands over much of the composition range examined. With the aid of second derivative spectra. the red absorption band has been resolved into three components. at 661.5. 674 and 680 nm. Fluoresccnce spectra have also been resolved into their principal components with some assistance from comparison with spectra of Chl in undecane solution containing DMMA. At room temperature (295 K) the resolvable components are of monomeric Chl at 670 nm. and of associated species at 681 and 725 nm. Fluorescence at 77 Kis of similar intensity but is distributed differently. in favor of longer-wave components. Corresponding to the 295 K components are emission bands at 675, 683–5 and 735 nm. Othcr components appear under certain conditions: at 695–700 nm when the Chl and DMMA conccntrations are both high, and at 705 nm whcn the ratio of DMMA to Chl is low. If DMMA is absent or at low concentration, much of the Chl exists as an aggregated form absorbing near 741 nm and fluorescing weakly near 760 nm at 77 K. Adsorption isotherms indicate some degree of cooperativity in the binding of Chl and DMMA to the particles. The photoreduction of p-dinitrobenzene by hvdrazobenzene. scnsitized by these particles, has been demonstrated     

CIRCULAR DICHROISM OF LIGHT-HARVESTING COMPLEXES FROM PURPLE PHOTOSYNTHETIC BACTERIA*

Abstract— The CD spectra of a range of antenna complexes from several different species of purple photosynthetic bacteria were recorded in the wavelength range of 190 to 930 nm. Analysis of the far UV CD (190 to 250 nm) showed that in each case except for the B800-850 from Chr. vinosum the secondary structure of the light-harvesting complexes contains a large amount of α-helix (?50%) and very little 0-pleated sheet. This confirms the predictions of the group of Zuber of a high a-helical content based upon consideration of the primary structures of several antenna apoproteins. The CD spectra from the carotenoids and the bacteriochlorophylls show considerable variations depending upon the type of antenna complex. The different amplitude ratios in the CD spectrum for the bacteriochlorophyll Qy, Qx and Soret bands indicate not only different degrees of exciton coupling, but also a strong and variable hyperchromism (Scherz and Parson, 1984a, b).