In vivo states and functions of carotenoids in an aerobic photosynthetic bacterium,Erythrobacter longus

In vivo states and functions of carotenoids in the membranes and the isolated RC-B865 pigment-protein complexes from an aerobic photosynthetic bacterium, Erythrobacter longus, are investigated by means of fluorescence excitation and resonance Raman (RR) spectra. Erythroxanthin sulfate, a dominant carotenoid species in the membranes (>70%), is found not to transfer the absorbed light energy to bacteriochlorophyll (Bchl), and its RR spectra are similar between the in vivo and in vitro states. These observations indicate that erythroxanthin sulfate does not interact with either Bchl or proteins in the membranes, and suggest that its function may be limited to photoprotection by quenching the harmful singlet oxygen. On the other hand, two other carotenoid species contained in the isolated RC-B865 complexes, zeaxanthin and bacteriorubixanthinal, have a high efficiency of energy transfer to Bchl (88±5%). The RR spectra of these two carotenoids, each of which can be selectively obtained by choosing the excitation wavelength, show some characteristics of interactions with proteins or Bchl.Abbreviations Bchl bacteriochlorophyll a - FWHM full width at half maximum - PAGE polyacrylamide gel electrophoresis - RC reaction center - RR resonance Raman - SDS sodium dodecyl sulfate     

Effects of α-benzyl-α-bromo-malodinitrile on the primary electron acceptor of Photosystem II in spinach chloroplasts

Reactions at the reducing side of Photosystem II in spinach chloroplasts are modified by α-benzyl-α-bromo-malodinitrile (BBMD).On addition of 50 μM BBMD to chloroplasts the following phenomena can be observed: (1) electron flow to an acceptor like 2,6-dichlorophenolindophenol is partly deflected to electron flow to oxygen; (2) the electron flow to oxygen is carbonyl cyanide m-chlorophenylhydrazone sensitive but 3-(3,4-dichlorophenyl)-1,1-dimethylurea insensitive; (3) variable fluorescence is abolished but basal fluorescence is not altered; (4) a strong photobleaching of carotenoids is induced. BBMD seems a very efficient acceptor for electrons from the primary electron acceptor of Photosystem II, resulting in a BBMD-mediated electron transport from this primary acceptor to oxygen.On pretreatment of chloroplasts with 50 μM BBMD the effects are different; (1) electron flow to 2,6-dichlorophenolindophenol, ferricyanide, or NADP is almost completely inhibited and is not restored by addition of artificial electron donors: (2) no electron flow to oxygen is observable unless BBMD again is added to reaction media; (3) no variable fluorescence is observable but basal fluorescence is not affected; (4) there is no photobleaching of carotenoids unless BBMD again is added; (5) no reduction of C-550 can be recorded. Pretreatment of chloroplasts with BBMD seems to induce an intense cycling of electrons around Photosystem II and only anew added BBMD can interrupt this cycling.     

Triplet states of bacteriochlorophyll and carotenoids in chromatophores of photosynthetic bacteria

Chromatophores from photosynthetic bacteria were excited with flashes lasting approx. 15 ns. Transient optical absorbance changes not associated with the photochemical electron-transfer reactions were interpreted as reflecting the conversion of bacteriochlorophyll or carotenoids into triplet states. Triplet states of various carotenoids were detected in five strains of bacteria; triplet states of bacteriochlorophyll, in two strains that lack carotenoids. Triplet states of antenna pigments could be distinguished from those of pigments specifically associated with the photochemical reaction centers. Antenna pigments were converted into their triplet states if the photochemical apparatus was oversaturated with light, if the primary photochemical reaction was blocked by prior chemical oxidation of P-870 or reduction of the primary electron acceptor, or if the bacteria were genetically devoid of reaction centers. Only the reduction of the electron acceptor appeared to lead to the formation of triplet states in the reaction centers.In the antenna bacteriochlorophyll, triplet states probably arise from excited singlet states by intersystem crossing. The antenna carotenoid triplets probably are formed by energy transfer from triplet antenna bacteriochlorophyll. The energy transfer process has a half time of approx. 20 ns, and is about 1 × 10³ times more rapid than the reaction of the bacteriochlorophyll triplet states with O₂. This is consistent with a role of carotenoids in preventing the formation of singlet O₂ in vivo. In the absence of carotenoids and O₂, the decay half times of the triplet states are 70 μs for the antenna bacteriochlorophyll and 6–10 μs for the reaction center bacteriochlorophyll. The carotenoid triplets decay with half times of 2–8 μs.With weak flashes, the quantum yields of the antenna triplet states are in the order of 0.02. The quantum yields decline severely after approximately one triplet state is formed per photosynthetic unit, so that even extremely strong flashes convert only a very small fraction of the antenna pigments into triplet states. The yield of fluorescence from the antenna bacteriochlorophyll declines similarly. These observations can be explained by the proposal that singlet-triplet fusion causes rapid quenching of excited singlet states in the antenna bacteriochlorophyll.     

Properties of a pigment system consisting of carotenoids and reaction centre pigments in chromatophores of Rhodospirillum rubrum

A pigment system containing carotenoids and oxidised reaction centre pigments is present in chromatophores of Rhodospirillum rubrum and this pigment system may cause fluorescence quenching when a still unidentified chromatophore component is in its oxidised state. Besides by its action spectrum, this pigment system is characterised by the time course and level of light saturation of the effect. The quenching of bacteriochlorophyll fluorescence is abolished when the permeability of the chromatophore membranes is affected. The quenching effect is correlated with a reversible absorption decrease of B 880. A possible function for this pigment system is discussed.     

Fluorescence emission spectra of cells and subcellular preparations of a green photosynthetic bacterium. Effects of dithionite on the intensity of the emission bands

Fluorescence emission spectra were measured of intact cells and subcellular preparations of the green photosynthetic bacterium Prosthecochloris aestuarii in the presence and in the absence of dithionite. A 3–5-fold increase in bacteriochlorophyll a fluorescence at 816 nm occurred upon addition of dithionite in a membrane vesicle preparation (Complex I), in a photochemically active pigment-protein complex and in a bacteriochlorophyll a protein complex free from reaction centers. The pigment-protein complex showed a relatively strong long-wave emission band (835 nm) of bacteriochlorophyll a, which was preferentially excited by light absorbed at 670 nm and was not stimulated by dithionite. With Complex I, which contains some bacteriochlorophyll c in addition to bacteriochlorophyll a, a 3–4-fold stimulation of bacteriochlorophyll c emission was also observed. Emission bands at shorter wavelengths, probably due to artefacts, were quenched by dithionite. With intact cells, the effect of dithionite was smaller, and consisted mainly of an increase of bacteriochlorophyll a emission.

The results indicate that the strong increase in the yield of bacteriochlorophyll emission that occurred upon generating reducing conditions is, at least mainly, due to a direct effect on the light-harvesting systems, and does not involve the reaction center as had been earlier postulated.     

Influence of blue light on the structure stability of antenna complexes from Allochromatium minutissimum with different content of carotenoids

Effects of photooxidation of bacteriochlorophyll (absorbtion at 850 nm) from the light-harvesting complex LH2 of Alc. minutissimum membranes on the LH2 complex structure have been studied. Photooxidation was induced by blue light that is absorbed by carotenoids. Four samples with different levels (from 100% to 3–5%) and composition of carotenoids were obtained by inhibiting the carotenoid biosynthesis in bacteria with diphenylamine. Electrophoresis in polyacrylamide gel showed that after illumination LH2 complex contained all the oxidized bacteriochlorophyll. The carotenoid composition did not change after the oxidation of the main part of bacteriochlorophyll in the LH2 complex. The results suggest that oxidation takes place in the bacteriochlorophyll part, which is essential for the molecule optical properties (the system of double conjugated bonds is changed), but does not influence the stability of the structure of the LH2 complex.     

Absorption changes of carotenoids and bacteriochlorophyll in energized chromatophores of Rhodospirillum rubrum

The energization of Rhodospirillum rubrum chromatophores by the light, ATP, PP_i, by dark electron transfer via energy-coupling sites of the redox chain, by the combination of KC1 and valinomycin causes absorption changes of carotenoids and bacteriochlorophyll. These changes due to the absorption-band shifts of the pigments are sensitive to the uncoupler p-trifluoromethoxycarbonyl cyanide phenylhydrazone (FCCP) but not to the combination of KC1 and nigericin, which abolishes fluorescence changes of atebrin. Dithionite and ferricyanide depress the light-induced absorption changes of bacteriochlorophyll but have no inhibitory effect on the PP_i-induced changes. Analysis of bacteriochlorophyll absorption changes in the infra-red region shows that the photooxidation of bacteriochlorophyll reaction centers with the negative peak in the region of 890 nm is accompanied by red and blue shifts of bacteriochlorophyll absorption bands. These shifts are due to a transmembrane electrochemical gradient of H⁺ and a local electric field arising as a result of oxidation of the reaction centers. It appears that the superposition of the (1) red shift which is characterized by negative and positive peaks at 865 and 895 nm, respectively, and (2) photobleaching of bacteriochlorophyll reaction centers in the region of 890 nm cause overall absorption changes with the negative peak at 865 nm.     

The site of manganese function in photosynthetic electron transport system

The effects of Mn²⁺ on aerobic photobleaching of carotenoids, on photoreduction of 2,6-dichlorophenolindophenol (DCIP) and on fluorescence above 600 mμ of spinach chloroplasts washed with 0.8 M Tris-HC1 buffer were investigated. Carotenoids (mostly carotenes, lutein and violaxanthin) in the Tris-washed chloroplasts were irreversibly bleached by illumination with red light, while carotenoids in normal chloroplasts prepared with a low concentration of Tris-HC1 underwent no bleaching upon illumination. The photobleaching of carotenoids observed with Tris-washed chloroplasts was inhibited by Mn²⁺ (MnCl₂ or MnSO₄) as well as by some inhibitors of the Hill reaction such as dichlorophenyl-1,1-dimethylurea (DCMU), methylthio-4,6-bis-isopropylamino-s-triazine and o-phenanthroline or by reducing agents such as ascorbate plus tetramethyl-p-phenylene diamine (TMPD). DCIP photoreduction, which was deactivated by Tris, was reactivated to 50–80% of the rate for normal chloroplasts upon addition of Mn²⁺. The restored photoreduction of DCIP was inhibited by DCMU and carbonylcyanide m-chlorophenylhydrazone (CCCP). The steady-state fluorescence yield of normal chloroplasts measured at room temperature was lowered by Tris treatment, and the decreased yield was restored by adding Mn²⁺ as well as ascorbate plus TMPD. CCCP also lowered the yield; the yield was recovered by adding ascorbate plus TMPD. Determination of manganese in normal and Tris-washed chloroplasts showed that 30% of the manganese in chloroplast was removed with Tris. It was postulated that Mn²⁺ functions in the electron transport on the oxidizing side of Photosystem II at a site between water and an electron carrier (Y). CCCP as well as Tris inhibits the reduction of Y⁺ by Mn²⁺, and carotenoids are oxidized by Y⁺ which is reduced by ascorbate plus TMPD.     

Fluence rate and wavelength dependence of photobleaching in the cyanobacterium Anabaena variabilis

The fluence rate dependence of the photobleaching in the cyanobacterium Anabaena variabilis was studied under physiological conditions. According to the in-vivo absorption spectra measured every day during the 5 d exposition the phycobiliproteins are more sensitive to high fluence rates than chlorophyll a. The carotenoids are least sensitive, so that a relative, but not an absolute increase in the carotenoid content occurred. At very high fluence rates exceeding about 50 Wm^-2 white light the organisms were photokilled after 5 d of irradiation. Measurements of the nitrate concentrations during the experiments have shown that nitrate was not the limiting factor in these experiments. Analysis of the photobleaching kinetics at 13.5 Wm^-2 white light revealed that after about 8 d the contents of all the pigments studied have reached a new, constant level. After exposure of the photobleached cyanobacteria to low irradiances repigmentation occurred. Thus, photobleaching is a light adaptation process and not simply a photodamage phenomenon. Studying the wavelength dependence of photobleaching at a constant photon fluence rate of 4·10^-8 mol cm^-2 s^-1 we found that the photobleaching of both phycobiliproteins and chlorophyll a was exclusively caused by wavelengths absorbed by the phycobiliproteins, mainly phycoerythrocaynin, and red light absorbed by short wavelength chlorophyll. Wavelengths <520 nm were ineffective.     

Proton uptake and quenching of bacteriochlorophyll fluorescence in Rhodopseudomonas spheroides

The addition of the cyclic cofactor 2,3,5,6-tetramethyl-p-phenylenediamine (diaminodurene) to a suspension of chromatophores of Rhodopseudomonas spheroides causes a light-dependent quenching of bacteriochlorophyll fluorescence. This effect is similar to one observed in chloroplasts and related to proton uptake. It is distinct from the quenching operative through the redox state of the primary electron donor and acceptor, as shown by its sensitivity to uncouplers and ionophorous antibiotics. The quenching is dependent on light intensity and diaminodurene concentration, and has a pH optimum at 7.1 where up to 70% of the fluorescence could be quenched in the presence of 0.33 mM diaminodurene.     

Chlorophyll Fluorescence and Photon Yield of Oxygen Evolution in Iron-Deficient Sugar Beet (Beta vulgaris L.) Leaves

The response of sugar beet (Beta vulgaris L.) leaves to iron deficiency can be described as consisting of two phases. In the first phase, leaves may lose a large part of their chlorophyll while maintaining a roughly constant efficiency of photosystem II photochemistry; ratios of variable to maximum fluorescence decreased by only 6%, and photon yields of oxygen evolution decreased by 30% when chlorophyll decreased by 70%. In the second phase, when chlorophyll decreased below a threshold level, iron deficiency caused major decreases in the efficiency of photosystem II photochemistry and in the photon yield of oxygen evolution. These decreases in photosystem II photochemical efficiency were found both in plants dark-adapted for 30 minutes and in plants dark-adapted overnight, indicating that photochemical efficiency cannot be repaired in that time scale. Decreases in photosystem II photochemical efficiency and in the photon yield of oxygen evolution were similar when measurements were made (a) with light absorbed by carotenoids and chlorophylls and (b) with light absorbed only by chlorophylls. Leaves of iron-deficient plants exhibited a room temperature fluorescence induction curve with a characteristic intermediate peak I that increases with deficiency symptoms.     

Effect of Light with Different Spectral Composition on Cell Growth and Pigment Composition of the Membranes of Purple Sulfur Bacteria <Emphasis Type="Italic">Allochromatium minutissimum</Emphasis> and <Emphasis Type="Italic">Allochromatium vinosum</Emphasis>

The effect of light with different spectral composition: white, red and blue-green (the first one is absorbed by all the pigments of the cell, and the second and the third ones are absorbed by bacteriochlorophyll and carotenoids, respectively) on culture growth, carotenoid synthesis, and assembly of the light-harvesting complexes was studied for the purple sulfur bacteria Allochromatium (Alc.) minutissimum MSU and Alc. vinosum ATCC 17899. The working hypothesis on the growth of bacteria under blue-green illumination (absorbed by carotenoids) resulting in the inhibition of cell growth was tested. When equalizing the light by luxes, the intensity of illumination for each luminous flux was 1800 lx (white and red light, 4 W/m²; bluegreen light, 0.4 W/m²). The growth of the cells was recorded in white and red light, while in blue-green light an insignificant increase was observed only for Alc. vinosum at the end of the experiment (7–9 days). Regardless of the spectral composition of the light the B800-850 type LH2 complex was always assembled in Alc. minutissimum membranes, and two short-wave LH2 complexes of В800-820 and В800-840 type were assembled in the membranes of Alc. vinosum. Upon smoothing and increasing the luminous flux up to 6 W/m² for every illumination mode, both cultures grew with approximately equal rates in blue-green light. In the membranes of Alc. minutissimum and Alc. vinosum the same types of LH2 complexes were assembled as in the case of 1800 lx illumination. It was found that blue-green light did not inhibit cell growth. At illumination of the cells collected at the end of the experiment with blue-green light for 6 h, no photooxidation of BChl850 was registered. However, in the membranes from the cells oxygen-saturated at isolation, ~50% of BChl850 was oxidized after 30 minutes of illumination. In the course of cell growth, oxygen is probably completely consumed and anaerobic conditions develop inside the cell. Under these conditions, formation of reactive oxygen species, BChl photooxidation and inhibition of the cell growth become impossible.     

Structure and function of carotenoids in the photoreaction center from Rhodospirillum rubrum

The bacteriochlorophyll (P-800 and P-870) of the carotenoidless photoreaction center isolated from Rhodospirillum rubrum (strain G9) is bleached irreversibly when the preparations are exposed to intense near infrared light in the presence of oxygen. This effect is much smaller in preparations, extracted from the wild type, which contain, as shown earlier, 1 mol of spirilloxanthin per mol of P-870. This photodynamic effec is shown to be due to singlet O₂. The oxidation of adrenaline in the presence of superoxide dismutase and the oxidation of 1,3-diphenylisobenzofuran are used as reporter reactions. Singlet oxygen is presumably generated by the triplet-triplet energy transfer ³bacteriochlorophyll → O₂ (³Σ).Four purified bacterial carotenoids, spirilloxanthin, sphaeroidene, sphaeroidenone and chloroxanthin were attached onto the carotenoidless photoreaction center from strain G9 in nearly 1 : 1 mol ratios with respect to P-870. Once fixed, these carotenoids confer protection against the photodynamic bleaching of bacteriochlorophyll. The relative photoprotection efficiency was 1.0 for spirilloxanthin and sphaeroidene, 0.4 for chloroxanthin and 0.2 for sphaeroidenone. The fixed carotenoids display optical activity and their molar ellipticity appears to be correlated with their relative photoprotection efficiency. The efficiency of energy transfer to P-870 is 0.90 for sphaeroidene, 0.35 for sphaeroidenone, 0.30 for chloroxanthin and 0.20 for spirilloxanthin. The energy transfer efficiency from the carotenoids to bacteriochlorophyll is suggested to be governed by the rate of the internal conversion processes of the excited singlet state of the carotenoids.A study of the difference absorption and CD spectra of the reconstituted minus carotenoidless preparations leads to the interpretation that the fixed carotenoids are in a central monocis conformation.     

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     

Isolation and characterization of light harvesting bacteriochlorophyll · protein complexes from Rhodopseudomonas capsulata

The isolation of two native light harvesting bacteriochlorophyl · protein complexes from Rhodopseudomonas capsulata is described. The light harvesting bacteriochlorophyll I (B 875) has been isolated from the blue-green mutant Ala⁺ lacking both carotenoids and light harvesting bacteriochlorophyll II. Light harvesting bacteriochlorophyll I is associated with a protein (light harvesting band 2) of 12 000 molecular weight.Light harvesting bacteriochlorophyll II complex has been isolated from the mutant Y5 lacking a reaction center and light harvesting bacteriochlorophyll I. Light harvesting bacteriochlorphyll II (B 800 + 850) together with carotenoids is associated with two polypeptides (light harvesting bands 3 and 4) having molecular weights of about 8000 and 10 000 (sodium dodecyl sulfate polyacrylamide gel electrophoresis). A third protein (light harvesting band 1) is in the purified light harvesting II fraction (mol. wt. approx. 14 000), but not associated with bacteriochlorophyll or carotenoids. The amino acid composition of the 3 antenna pigment II proteins is given. The polarity of these proteins was found to be 48%. From the amino acid composition the following molecular weights were calculated band 1: 17 350, band 3: 13 350 and band 4: 10 500.     

Isolation and characterization of light harvesting bacteriochlorophyll.protein complexes from Rhodopseudomonas capsulata

The isolation of two native light harvesting bacteriochlorophyl.protein complexes from Rhodopseudomonas capsulata is described. The light harvesting bacteriochlorophyll I (B 875) has been isolated from the blue-green mutant A1a+ lacking both carotenoids and light harvesting bacteriochlorophyll II. Light harvesting bacteriochlorophyll I is associated with a protein (light harvesting band 2) of 12 000 molecular weight. Light harvesting bacteriochlorophyll II complex has been isolated from the mutant Y5 lacking a reaction center and light harvesting bacteriochlorophyll I. Light harvesting bacteriochlorphyll II (B 800 + 850) together with carotenoids is associated with two polypeptides (light harvesting bands 3 and 4) having molecular weights of about 8000 and 10 000 (sodium dodecyl sulfate polyacrylamide gel electrophoresis). A third protein (light harvesting band 1) is in the purified light harvesting II fraction (mol. wt. approx. 14 000), but not associated with bacteriochlorophyll or carotenoids. The amino acid composition of the 3 antenna pigment II proteins is given. The polarity of these proteins was found to be 48%. From the amino acid composition the following molecular weights were calculated band 1: 17 350, band 3: 13 350 and band 4: 10 500.     

Loss of the precise control of photosynthesis and increased yield of non‐radiative dissipation of excitation energy after mild heat treatment of barley leaves

The after effects of a short exposure of intact barley leaves to moderately elevated temperature (40°C, 5 min) on the induction transients and the irradiance dependencies of photosynthesis and chlorophyll fluorescence are presented. This mild heat treatment strongly reduced the oscillations in the rate of photosynthesis and in the yield of chlorophyll fluorescence. However, only a 25% irreversible inhibition of maximum photosynthetic capacity of photosystem II (PSII) measured by oxygen evolution was produced and the intrinsic quantum yield of PSII measured by the chlorophyll fluorescence ratio (F_m‐ F_o)/F_m decreased by only 15%. In contrast, the above treatment increased radiationless dissipation processes in PSII by a factor of two. In heat‐treated leaves, photosynthesis was not saturated even by strong light. Both ΔpH‐dependent quenching of excitons in PSII (including formation of zeaxanthin) and state 1/state 2 transition were found to be stimulated. Heat exposure enhanced the control of PSII activity by PSI, as evidenced by a significant increase in the quenching effect of far‐red light on the maximum yield of chlorophyll fluorescence. It was deduced that after mild heat treatment, the photosynthetic apparatus in leaves lacks the precise coordinating control of electron transport and carbon metabolism owing to the inability of PSII to support electron transport at a level adequate for carbon metabolism. This effect was not related to the small irreversible thermal damage to PSII, but was rather due to a significant increase in non‐photochemical quenching of excitation energy.     

The formation of bacteriochlorophyll · protein complexes of the photosynthetic apparatus of Rhodopseudomonas capsulata during early stages of development

Cells of Rhodopseudomonas capsulata cultivated at an oxygen partial pressure of 400 mmHg in the dark contained 0.1 nmol or less total bacteriochlorophyll per mg membrane protein. The bacteriochlorophyll was found in the reaction center (10 pmol bacteriochlorophyll/mg membrane protein) and in the light harvesting bacteriochlorophyll I but not in the light harvesting bacteriochlorophyll II. Formation of the photosynthetic apparatus in those cells was induced by incubation at a very low oxygen tension in the dark. Reaction center bacteriochlorophyll and light harvesting bacteriochlorophyll increased three fold after 60 min of incubation at 1–2 mmHg (pO₂). Light harvesting bacteriochlorophyll II increased strongly after 60 min and became dominating after 90 min of incubation. The total bacteriochlorophyll content doubled every 30 min, but synthesis of reaction center bacteriochlorophyll proceeded at much lower rates. Consequently the size of the photosynthetic unit (total bacteriochlorophyll/reaction center bacteriochlorophyll) increased from 15 to 52 during 150 min of incubation. The proteins of the photosynthetic apparatus were synthesized concomitantly with bacteriochlorophyll.Cells which were incubated at 0.5 mmHg (pO₂) do not grow but form the photosynthetic apparatus. During the first hours of incubation light harvesting bacteriochlorophyll I and reaction center bacteriochlorophyll were the dominant bacteriochlorophyll species, but light harvesting bacteriochlorophyll II was synthesized only in small amounts. Total bacteriochlorophyll and reaction center bacteriochlorophyll increased from 30 min up until 210 min of incubation more than 10 fold. The final concentrations of total bacteriochlorophyll and reaction center bacteriochlorophyll were 8.6 nmol and 0.26 nmol per mg membrane protein, respectively. The three protein components of the reaction centers (mol. wts. 28 000, 24 000 and 21 000) and the protein of the light harvesting I complex (mol. wt. 12 000) were incorporated simultaneously. The protein of band 1 (mol. wt. 14 000) which was present in the isolated light harvesting complex II, was synthesized only in very small amounts. The proteins of bands 3 and 4 (mol. wt. 10 000 and 8000) however, which were shown to be associated with light harvesting bacteriochlorophyll II, were synthesized in noticeable amounts as was light harvesting bacteriochlorophyll II. In addition a protein with an apparent molecular weight of 45 000 showed a strong incorporation of ¹⁴C-labeled amino acids. This protein comigrates with one protein which was found to be associated with a green pigment excreted during incubation at 0.5 Torr into the medium. The in vivo-absorption maxima of this pigment complex were 660, 590, 540, 417 and 400 nm. The succinate oxidase and the NADH oxidase seemed to be incorporated into the newly formed intracytoplasmic membrane only in very small amounts. Thus, reaction center and light harvesting bacteriochlorophyll and their associated proteins were simultaneously synthesized, whereas light harvesting complex II is the variable part of the photosynthetic apparatus.     

Comparison of extracellular ATP and UTP signalling in rat renal mesangial cells. No indications for the involvement of separate purino- and pyrimidino-ceptors.

The visible c.d. spectrum of wild-type Rhodospirillum rubrum shows positive bands [Dratz, Schultz & Sauer (1966) Brookhaven Symp. Biol. 19, 303-318] that are largely due to the B880 antenna pigments, bacteriochlorophyll a and carotenoids. The bacteriochlorophyll c.d. band was absent from the spectrum of R. rubrum G9, a mutant unable to synthesize coloured carotenoids, and could be partly restored by adding extracted carotenoids to freeze-dried membrane vesicles isolated from that mutant. Therefore it seems to arise from either bacteriochlorophyll-carotenoid interactions or bacteriochlorophyll-protein interactions that are induced by the carotenoid. The more complex carotenoid c.d. band had different shapes in native and reconstituted carotenoid-containing membranes. Such differences suggest that the optical activity of the carotenoid in the B880 antenna arises from both non-degenerate and degenerate interactions.     

State transitions,photosystem stoichiometry adjustment and non-photochemical quenching in cyanobacterial cells acclimated to light absorbed by photosystem I or photosystem II

Cells of the cyanobacterium Synechococcus 6301 were grown in yellow light absorbed primarily by the phycobilisome (PBS) light-harvesting antenna of photosystem II (PS II), and in red light absorbed primarily by chlorophyll and, therefore, by photosystem I (PS I). Chromatic acclimation of the cells produced a higher phycocyanin/chlorophyll ratio and higher PBS-PS II/PS I ratio in cells grown under PS I-light. State 1-state 2 transitions were demonstrated as changes in the yield of chlorophyll fluorescence in both cell types. The amplitude of state transitions was substantially lower in the PS II-light grown cells, suggesting a specific attenuation of fluorescence yield by a superimposed non-photochemical quenching of excitation. 77 K fluorescence emission spectra of each cell type in state 1 and in state 2 suggested that state transitions regulate excitation energy transfer from the phycobilisome antenna to the reaction centre of PS II and are distinct from photosystem stoichiometry adjustments. The kinetics of photosystem stoichiometry adjustment and the kinetics of the appearance of the non-photochemical quenching process were measured upon switching PS I-light grown cells to PS II-light, and vice versa. Photosystem stoichiometry adjustment was complete within about 48 h, while the non-photochemical quenching occurred within about 25 h. It is proposed that there are at least three distinct phenomena exerting specific effects on the rate of light absorption and light utilization by the two photoreactions: state transitions; photosystem stoichiometry adjustment; and non-photochemical excitation quenching. The relationship between these three distinct processes is discussed.Abbreviations Chl chlorophyll - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - F relative fluorescence intensity at emission wavelength nm - F _o fluorescence intensity when all PS II traps are open - light 1 light absorbed preferentially by PS I - light 2 light absorbed preferentially by PS II - PBS phycobilisome - PS photosystem