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PubMed2002

Carotenoid to chlorophyll energy transfer in the peridinin-chlorophyll-a-protein complex involves an intramolecular charge transfer state.

Carotenoids are, along with chlorophylls, crucial pigments involved in light-harvesting processes in photosynthetic organisms. Details of carotenoid to chlorophyll energy transfer mechanisms and their dependence on structural variability of carotenoids are as yet poorly understood. Here, we employ femtosecond transient absorption spectroscopy to reveal energy transfer pathways in the peridinin-chlorophyll-a-protein (PCP) complex containing the highly substituted carotenoid peridinin, which includes an intramolecular charge transfer (ICT) state in its excited state manifold. Extending the transient absorption spectra toward near-infrared region (600-1800 nm) allowed us to separate contributions from different low-lying excited states of peridinin. The results demonstrate a special light-harvesting strategy in the PCP complex that uses the ICT state of peridinin to enhance energy transfer efficiency.

Journal Article↗
PubMed1972

In Vitro Photoreactions of Chlorophyll and Photosynthetic Energy Conversion: Chlorophyll-Quinone-Ethanol at Low Temperature as an Analog of Photosystems I and II.

Illumination at low temperatures of ethanol solutions of p-benzoquinone, alone or in the presence of chlorophyll or pheophytin, leads to the reversible formation of radical complexes. Based on g-value determinations and deuterium-substitution effects, the radicals are identified as a semiquinone and an ethoxy radical. In the porphyrin-sensitized system, ternary complexes are produced. Chlorophyll also forms a cation radical upon illumination, whereas pheophytin does not. The generation of this cation radical is independent of the presence of quinone, and proceeds via the chlorophyll singlet state, as opposed to quinone and ethoxy radical production, which involve triplet states. The significance of these reactions to photosynthetic energy conversion is discussed.

Journal Article↗
PubMed1976

Covalently linked chlorophyll a dimer: A biomimetic model of special pair chlorophyll.

The synthesis of a covalent dimer of chlorophyll a which possesses properties strikingly similar to those exhibited by P700 special pair chlorophyll in vivo is described. The covalent dimer is characterized by several spectroscopic techniques. Hydrogen bonding nucleophiles, such as water, primary alcohols, and primary thiols, are effective in generating a species from solutions of 10 muM covalent dimer in hydrophobic solvents which absorbs light near 700 nm. Formation of this in vitro special pair is a rapid, spontaneous process at room temperature. The range of nucleophiles which promote this process suggests that amino acid residues may function in a similar fashion to form P700 in chlorophyll-protein complexes. The photochemical properties of this in vitro special pair mimic those of in vivo P700 species. The 697 nm absorption of the in vitro special pair undergoes photo-bleaching rapidly in the presence of iodine that results in the production of a cation radical which exhibits an electron spin resonance signal similar to that of oxidized P700 observed in Chlorella vulgaris.

Journal Article↗
PubMed1975

Events Surrounding the Early Development of Euglena Chloroplasts: VI. Action Spectra for the Formation of Chlorophyll, Lag Elimination in Chlorophyll Synthesis, and Appearance of TPN-dependent Triose Phosphate Dehydrogenase and Alkaline DNase Activities.

Action spectra derived from dose-response curves measured for various processes associated with chloroplast development in Euglena gracilis var. bacillaris are presented. The action spectrum for chlorophyll synthesis during the first 36 hours of continuous illumination of dark-grown resting cells resembles the absorption spectrum of protochlorophyll(ide). The action spectrum for the preillumination phase of potentiation, during which preillumination followed by a dark period brings about lag elimination in chlorophyll synthesis when the cells are subsequently exposed to postilluminating light, shows a high peak in the blue region (at about 433 nm) with a small peak in the yellow-orange region (at about 597 nm); the postillumination phase yields an action spectrum very similar to that obtained for chlorophyll synthesis in continuous light in normal, unpotentiated cells, with peaks at 433 and 631 nm. Alkaline DNase and TPN-linked triose phosphate dehydrogenase, two plastid enzymes which are synthesized outside the chloroplast, yield action spectra which are consistent with protochlorophyll(ide) being the major light receptor. The action spectra which implicate pigments resembling protochlorophyll(ide) holochrome have blue to red peak ratios in the vicinity of 5:1 as does the absorption spectrum of the protochlorophyllide holochrome from beans; the action spectrum is not identical with the holochrome spectrum indicating that the Euglena holochrome may differ from the bean pigment in details of its absorption spectrum. The action spectrum for preillumination, shows a ratio of the blue peak to the red effectiveness of about 24:1. This suggests that preillumination is controlled by a photoreceptor different from the protochlorophyll(ide) holochrome.

Journal Article↗
PubMed2004

Simultaneous determination of chlorophyll a and chlorophyll b by derivative spectrophotometry.

Chlorophyll a (Chl a) and chlorophyll b (Chl b) plant pigments, which are important in the food industry and are beneficial as environmental pollution indicators, have been extracted with a novel solvent mixture (1:1 v/v acetone-propanol) not containing chloroform and simultaneously determined by first-derivative spectrophotometry. The results were statistically compared to those obtained by the ordinary absorption spectrophotometric reference utilizing the principle of additivity of absorbances. The testing of the developed method in synthetic mixtures of Chl a and Chl b and in real plant material samples (grass, spinach, chard, purslane, black cabbage, crisp lettuce, rocket, dill and seaweed) proved successful in that the developed extractive derivative spectrophotometric method was both rapid and precise, and was not dependent on the Chl a/b ratio in contrast to the reference method which was adversely affected by the latter parameter.

Calibration↗
PubMed2005

Reconstitution of the peridinin-chlorophyll a protein (PCP): evidence for functional flexibility in chlorophyll binding.

The coding regions for the N-domain, and full length peridinin-chlorophyll a apoprotein (full length PCP), were expressed in Escherichia coli. The apoproteins formed inclusion bodies from which the peptides could be released by hot buffer. Both the above constructs were reconstituted by addition of a total pigment extract from native PCP. After purification by ion exchange chromatography, the absorbance, fluorescence excitation and CD spectra resembled those of the native PCP. Energy transfer from peridinin to Chl a was restored and a specific fluorescence activity calculated which was approximately 86% of that of native PCP. Size exclusion analysis and CD spectra showed that the N-domain PCP dimerized on reconstitution. Chl a could be replaced by Chl b, 3-acetyl Chl a, Chl d and Bchl using the N-domain apo protein. The specific fluorescence activity was the same for constructs with Chl a, 3-acetyl Chl a, and Chl d but significantly reduced for those made with Chl b. Reconstitutions with mixtures of chlorophylls were also made with eg Chl b and Chl d and energy transfer from the higher energy Qy band to the lower was demonstrated.

Carotenoids↗
PubMed1987

Chlorophyll-protein composition of the thylakoid membrane from Prochlorothrix hollandica, a prokaryote containing chlorophyll b.

The chlorophyll-protein complexes of the thylakoid membrane from Prochlorothrix hollandica were identified following electrophoresis under nondenaturing conditions. Five complexes, CP1-CP5, were resolved and these green bands were analyzed by spectroscopic and immunological methods. CP1 contains the photosystem I (PSI) reaction center, as this complex quenched fluorescence at room temperature, and had a 77 K fluorescence emission peak at 717 nm. CP4 contains the major chlorophyll-a-binding proteins of the photosystem II (PSII) core, because this complex contained polypeptides which cross-reacted to antibodies raised against Chlamydomonas PSII proteins 5 and 6. Furthermore, fluorescence excitation studies at 77 K indicated that only a Chl a is bound to CP4. Complexes CP2, CP3 and CP5 contained functionally bound Chl a and b as judged by absorption spectroscopy at 20 degrees C and fluorescence excitation spectra at 77 K. CP2, CP3 and CP5 all contain polypeptides of 30-33 kDa which are immunologically distinct from the LHC-II complex of higher plant thylakoids.

Chlorophyll↗
PubMed2000

[A comparative study on chlorophyll content, chlorophyll fluorescence and diurnal course of leaf gas exchange of two ecotypes of banyan].

The morphological differences, chlorophyll contents, fluorescence and diurnal course of leaf gas exchange between terrestrial banyan and amphibious banyan were compared with pot culture. The amphibious banyan possesses well developed aerial and hydro-adventitious roots, and wider leaf with inclination of evolution toward mesophytic traits. The chlorophyll content of terrestrial banyan was higher than that of amphibious banyan. The diurnal course of leaf gas exchange indicated that net photosynthetic rate of terrestrial banyan was slightly higher than that of amphibious banyan grown in water, but much higher than that grown in soil. The amphibious banyan grown in water had the highest transpiration rate, the terrestrial banyan had a lower one, and the amphibious banyan grown in soil had the lowest. Linear regression analysis showed a positive correlation between net photosynthetic rate and stomatal conductance, implying that the stomatal conductance was dominant factor controlling the gas exchange. In this study, the term of intrinsic water use efficiency (net photosynthetic rate/stomatal conductance ratio, Intrinsic WUE) was applied to describe the photosynthesis and water properties, and the result showed that it was a more suitable measure compared to the usual WUE(net photosynthetic rate/transpiration rate). Among the three banyan plants examined, the amphibious banyan had the highest intrinsic WUE.

Adaptation, Physiological↗
PubMed2004

Chlorophyll breakdown in tobacco: on the structure of two nonfluorescent chlorophyll catabolites.

In extracts of senescent leaves of the tobacco plant Nicotiana rustica, two colorless compounds with UV/VIS characteristics of nonfluorescent chlorophyll catabolites (NCCs) were detected and tentatively identified as Nr-NCCs. These two polar NCCs were found in similar amounts in the fresh extracts, and their constitutions could be determined by spectroscopic analysis. The data showed both of the two Nr-NCCs to have the same tetrapyrrolic core structure, as reported previously for all other NCCs from senescent higher plants. In the less polar catabolite, named Nr-NCC-2, this core structure was conjugated with a glucopyranose unit, as similarly discovered earlier in Bn-NCC-2, an NCC from oilseed rape (Brassica napus). The more polar NCC from tobacco leaves, Nr-NCC-1, carried an additional malonyl substituent at the 6'-OH group of the glucopyranosyl moiety. Partial (enzyme-catalyzed) hydrolysis of Nr-NCC-1 gave Nr-NCC-2, while enzyme-catalyzed malonylation of Nr-NCC-2 gave Nr-NCC-1, establishing the identity of their basic tetrapyrrole structure. In earlier work (on the polar NCCs from oilseed rape), only separate glucopyranosyl and malonyl functionalities were detected. Nr-NCC-1, thus, represents a further variant of the structures of NCCs from senescent higher plants and exhibits an unprecedented peripheral refunctionalization in chlorophyll catabolites.

Chlorophyll↗
PubMed1991

Chlorophyll a/b binding (CAB) polypeptides of CP29, the internal chlorophyll a/b complex of PSII: characterization of the tomato gene encoding the 26 kDa (type I) polypeptide, and evidence for a second CP29 polypeptide.

CP29, the core chlorophyll a/b (CAB) antenna complex of Photosystem II (PSII), has two nuclear-encoded polypeptides of approximately 26 and 28 kDa in tomato (Lycopersicon esculentum). Cab9, the gene for the Type I (26 kDa) CP29 polypeptide was cloned by immunoscreening a tomato leaf cDNA library. Its identity was confirmed by sequencing tryptic peptides from the mature protein. Cab9 is a single-copy gene with five introns, the highest number found in a CAB protein. In vitro transcription-translation gave a 31 kDa precursor which was cleaved to about 26 kDa after import into isolated tomato chloroplasts. The Cab9 polypeptide has the two highly conserved regions common to all CAB polypeptides, which define the members of this extended gene family. Outside of the conserved regions, it is only slightly more closely related to other PSII CABs than to PSI CABs. Sequence analysis of tryptic peptides from the Type II (28 kDa) CP29 polypeptide showed that it is also a member of the CAB family and is very similar or identical to the CP29 polypeptide previously isolated from spinach. All members of the CAB family have absolutely conserved His, Gln and Asn residues which could ligate the Mg atoms of the chlorophylls, and a number of conserved Asp. Glu, Lys and Arg residues which could form H-bonds to the polar groups on the porphyrin rings. The two conserved regions comprise the first and third predicted trans-membrane helices and the stroma-exposed segments preceding them.

Amino Acid Sequence↗
PubMed2005

Evidence for localisation of accumulated chlorophyll cation on the D1-accessory chlorophyll in the reaction centre of photosystem II.

Absorption and circular dichroism spectra of Photosystem II (PS II) reaction centres (RC) were studied and compared with spectra calculated on the basis of point-dipole approximation. Chlorophyll cation was accumulated during a light treatment of PS II RC in the presence of artificial electron acceptor silicomolybdate. Light-induced difference spectra and their calculated counterparts revealed the location of accumulated cation at the accessory chlorophyll of the D1 protein subunit.

Cations↗
PubMed1979

Photoinduced charge separation in liposomes containing chlorophyll a. I. Photoreduction of copper(II) by potassium ascorbate through liposome bilayer containing purified chlorophyll a.

Photosensitivity of dispersion of phosphatidylcholine bilayer liposomes containing purified chlorophyll alpha was examined. The reduction of Cu(II) in the solution outside liposomes was observed upon illumination with visible light under anaerobic condition by means of ESR. The rate of photoreduction was significantly increased by a reductant, potassium ascorbate, localized in the solution of the opposite side of the membrane. The aciton spectrum of the reduction agreed with the absorption spectrum of chlorphyll a in the dispersion. The amount of bleach chlorophyll a was negligible compared with that of reduced (Cu(II). These facts lead to the conclusion that the potoinduced redox reactions at both the membrane-solution interfaces are coupled with each other through the bilayer of each liposome. Kinetic analysis of the reactions based on a possible reaction scheme was carried out and some of the kinetic parameters were determined.

Anaerobiosis↗
PubMed2002

Photosystem II reaction center with altered pigment-composition: reconstitution of a complex containing five chlorophyll a per two pheophytin a with modified chlorophylls.

Pigment-depleted Photosystem II reaction centers (PS II-RCs) from a higher plant (pea) containing five chlorophyll a (Chl) per two pheophytin a (Phe), were treated with Chl and several derivatives under exchange conditions [FEBS Lett. 434 (1998) 88]. The resulting reconstituted complexes were compared to those obtained by pigment exchange of "conventional" PS II-RCs containing six Chl per two Phe. (1) The extraction of one Chl is fully reversible. (2) The site of extraction is the same as the one into which previously extraneous pigments have been exchanged, most likely the peripheral D1-H118. (3) Introducing an efficient quencher (Ni-Chl) into this site results in only 25% reduction of fluorescence, indicating incomplete energy equilibration among the "core" and peripheral chlorophylls.

Binding Sites↗
PubMed1988

500 MHz 1H NMR of chlorophylls in the major light-harvesting chlorophyll-protein complex of photosystem II.

500 MHz 1H NMR spectra were obtained of solutions containing oligomeric and monomeric forms of Chl a/b-P2, the major light-harvesting chlorophyll a/b-protein complex of photosystem II, isolated from thylakoid membranes of barley (Hordeum vulgare). Oligomers showed only a broad unresolved spectrum, but for monomers several downfield-shifted chlorophyll proton resonances were observed, assigned to the alpha and beta methine protons and the formyl proton of Chl-b. Identifying the observed shifts as ring-current shifts, these NMR data can be matched with previously obtained optical data confirming the trimeric arrangement of Chl-b in Chl a/b-P2 protein, with a distance between the chromophore centers of approximately 12 A.

Chlorophyll↗
PubMed1972

Migration of electronic energy from chlorophyll b to chlorophyll a in solutions.

Absorption, emission, and fluorescence excitation spectra of pure solutions of chlorophyll a (Chl a) and chlorophyll b (Chl b) in diethyl ether and of equimolecular mixed solutions of the two pigments, were determined at room temperature as functions of concentration (in the range from 5 x 10(-6) M to 4 x 10(-3) M) and of wavelength of the exciting light (in the regions 380-465 and 550-650 nm). The efficiency of energy transfer from Chl b to Chl a, derived from these data, was found to depend on the wavelength of exciting light. Furthermore, the transfer efficiency calculated from sensitization of Chl a fluorescence by Chl b was substantially smaller than that calculated from quenching of Chl b fluorescence by Chl a. Both these effects are tentatively explained as evidence of superposition of a "fast" energy transfer (taking place before the Boltzmann distribution of vibrational energy had been reached) upon the "delayed" transfer, which takes place after vibrational equilibration. The first-named mechanism is made possible by overlapping of the absorption bands of the two pigments; the second, by overlapping of the emission band of Chl b and the absorption band of Chl a. The first mechanism can lead to repeated transfer of excitation energy between pigment molecules, the second only to a one-time transfer from the donor to the acceptor. Both mechanisms could be of the same, second-order type, with the transfer rate proportional to r(-6). An alternative is for the fast mechanism to be of the first order, with the transfer rate proportional to r(-3), but spectroscopic evidence seems to make this alternative less probable.

Chlorophyll↗
PubMed2003

Recombinant water-soluble chlorophyll protein from Brassica oleracea var. Botrys binds various chlorophyll derivatives.

A gene coding for water-soluble chlorophyll-binding protein (WSCP) from Brassica oleracea var. Botrys has been used to express the protein, extended by a hexahistidyl tag, in Escherichia coli. The protein has been refolded in vitro to study its pigment binding behavior. Recombinant WSCP was found to bind two chlorophylls (Chls) per tetrameric protein complex but no carotenoids in accordance with previous observations with the native protein [Satoh, H., Nakayama, K., Okada, M. (1998) J. Biol. Chem. 273, 30568-30575]. WSCP binds Chl a, Chl b, bacteriochlorophyll a, and the Zn derivative of Chl a but not pheophytin a, indicating that the central metal ion in Chl is essential for binding. WSCP also binds chlorophyllides a and b and even the more distant Chl precursor Mg-protoporphyrin IX; however, these pigments fail to induce oligomerization of the protein. We conclude that the phytol group in bound Chl plays a role in the formation of tetrameric WSCP complexes. If WSCP in fact binds Chl or its derivative(s) in vivo, the lack of carotenoids in pigmented WSCP raises the question of how photooxidation, mediated by triplet-excited Chl and singlet oxygen, is prohibited. We show by spin-trap electron-paramagnetic resonance that the light-induced singlet-oxygen formation of WSCP-bound Chl is lower by a factor of about 4 than that of unbound Chl. This as-yet-unknown mechanism of WSCP to protect its bound Chl against photooxidation supports the notion that WSCP may function as a transient carrier of Chl or its derivatives.

Brassica↗
PubMed2002

Chlorophyll biosynthesis. Expression of a second chl I gene of magnesium chelatase in Arabidopsis supports only limited chlorophyll synthesis.

Magnesium (Mg) chelatase is a heterotrimeric enzyme complex that catalyzes a key regulatory and enzymatic reaction in chlorophyll biosynthesis, the insertion of Mg(2+) into protoporphyrin IX. Studies of the enzyme complex reconstituted in vitro have shown that all three of its subunits, CHL I, CHL D, and CHL H, are required for enzymatic activity. However, a new T-DNA knockout mutant of the chlorina locus, ch42-3 (Chl I), in Arabidopsis is still able to accumulate some chlorophyll despite the absence of Chl I mRNA and protein. In barley (Hordeum vulgare), CHL I is encoded by a single gene. We have identified an open reading frame that apparently encodes a second Chl I gene, Chl I2. Chl I1 and Chl I2 mRNA accumulate to similar levels in wild type, yet CHL I2 protein is not detectable in wild type or ch42-3, although the protein is translated and stromally processed as shown by in vivo pulse labeling and in vitro chloroplast imports. It is surprising that CHL D accumulates to wild-type levels in ch42-3, which is in contrast to reports that CHL D is unstable in CHL I-deficient backgrounds of barley. Our results show that limited Mg chelatase activity and CHL D accumulation can occur without detectable CHL I, despite its obligate requirement in vitro and its proposed chaperone-like stabilization and activation of CHL D. Thus, the unusual post-translational regulation of the CHL I2 protein provides an opportunity to study the different steps involved in stabilization and activation of the heterotrimeric Mg chelatase in vivo.

Amino Acid Sequence↗
PubMed1983

Immunological evidence for apoproteins of the light-harvesting chlorophyll-protein complex in a mutant of barley lacking chlorophyll b.

A barley mutant lacking chlorophyll b and the pigmented light-harvesting chlorophyll-protein of photo-system 2 is shown by several criteria to contain functional apoproteins of the light-harvesting complex. 1. Electrophoretic comparison of thylakoid polypeptide patterns, and the effects of trypsin treatment on these, suggests that the mutant contains several polypeptides equivalent in mobility to those of the wild-type complex. 2. An antibody monospecific for the light-harvesting complex agglutinated both wild-type and mutant thylakoids. 3. 'Western blot' immunoelectrophoretic analysis indicated that of four distinct subunits of the light-harvesting complex in the wild-type thylakoids, three are detectable in the mutant. 4. As in wild-type lamellae at least one of the light-harvesting complex polypeptides is phosphorylated by the endogenous protein kinase. The results are considered in terms of a general role for the light-harvesting complex polypeptides in membrane appression and the regulation of excitation energy distribution within thylakoids.

Chlorophyll↗