Two pigment proteins in spinach chloroplasts

Do HOMO-LUMO Energy Levels and Band Gaps Provide Sufficient Understanding of Dye-Sensitizer Activity Trends for Water Purification?

A dye-sensitized solar cell assembly can be used to harvest solar energy, while suitable dye sensitizers can be used to purify water. Here, we characterized the activity trends of four dye sensitizers, namely, PORPC-1, PORPC-2, PORPC-3, and PORPC-4, for water purification applications using density functional theory (DFT) with the Perdew-Burke-Ernzerhof (PBE), B3LYP, and PBE0 functionals, ΔSCF, time-dependent DFT (TD-DFT), and quasiparticle Green's function (GW) methods. The energy levels of the highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs) were calculated using gas-phase and aqueous-phase methods in order to understand charge-injection abilities and the dye regeneration processes. PBE, B3LYP, PBE0, and TD-DFT methods failed to predict PORPC-4 to be the best sensitizer, while PORPC-2 and PORPC-4 were predicted to be the best sensitizers using ΔSCF coupled with the implicit solvation method, and HOMO-LUMO energies were corrected for the aqueous environment in the GW calculations. However, none of these methods accurately predicted the performance trend of all four dye sensitizers. Consequently, we used the aggregation assembly patterns of the dye molecules in an aqueous environment to further probe the activity trends and found that PORPC-3 and PORPC-4 prefer J-aggregated assembly patterns, whereas PROPC-1 and PORPC-2 prefer to be H-aggregated. Therefore, the performance of these dye molecules can be determined by combining HOMO-LUMO energy levels with aggregate-assembly patterns, with the activity trend predicted to be PORPC-4 > PORPC-2 > PORPC-3 > PORPC-1, which is in good agreement with experimental findings.

Higher plant chloroplasts: Evidence that all the chlorophyll exists as chlorophyll-protein complexes

By using the polyacrylamide gel electrophoresis system described in this report, it was possible to fractionate all the photosynthetic pigments of maize (Zea mays L.) thylakoids into chlorophyll-protein complexes with negligible formation of free or detergent-complexed chlorophyll. Identical sodium dodecyl sulfate extracts of thylakoids have previously resulted in up to 50% of the chlorophyll migrating as free chlorophyll after electrophoresis. The major difference from previous gel electrophoresis systems is the replacement of sodium dodecyl sulfate in the electrophoresis buffer by Deriphat 160 (disodium N-lauryl-beta-iminodipropionate), a zwitterionic detergent. The results suggest that: (i) no significant amount of free chlorophyll exists in the chloroplast thylakoid membranes in vivo, and (ii) most of the free pigment seen previously on gels was generated during the electrophoresis and was not a result of the solubilization technique. Additionally, the new chlorophyll-protein complexes resolved appear to have different characteristics (pigment content and size) that those observed in former systems.

Lithium dodecyl sulfate/polyacrylamide gel electrophoresis of thylakoid membranes at 4 degrees C: Characterizations of two additional chlorophyll a-protein complexes

Lithium dodecyl sulfate/polyacrylamide gel electrophoresis of Chlamydomonas reinhardtii thylakoid membranes at room temperature gave two chlorophyll-protein complexes, CP I and CP II, as had been reported previously. However, when the electrophoresis was performed at 4 degrees C, there was an increase in the amount of chlorophyll associated with CP I and CP II, and in addition, three other chlorophyll-protein complexes appeared. Two of these complexes, designated CP III and CP IV, were characterized and found to be similar in their compositions. Each complex contains four to five molecules of chlorophyll a, one molecule of beta-carotene, and one polypeptide chain. The apoprotein of CP III is polypeptide 5 (M(r) 50,000) and that of CP IV is polypeptide 6 (M(r) 47,000); the two polypeptides are structurally unrelated. Chlorophyll-protein complexes similar to C. reinhardtii CP III and CP IV were also detected in higher plants (e.g., Pisum sativum). The apoproteins of the higher plant complexes are immunochemically related to those of the C. reinhardtii complexes, as shown by crossed immunoelectrophoresis. Absorption spectra of CP III and CP IV at -196 degrees C revealed a component at 682 nm. This observation, together with the previous results on photosystem II mutants [Chua, N.-H. & Bennoun, P. (1975) Proc. Natl. Acad. Sci. USA 72, 2175-2179], provides indirect evidence that CP III and CP IV may be involved in the primary photochemistry of photosystem II.

Theory of picosecond-laser-induced fluorescence from highly excited complexes with small numbers of chromophores

The problem of singlet excitation kinetics and dynamics, especially at high excitation intensities, among a small number of chromophores of a given system has been addressed. A specific scheme for the kinetics is suggested and applied to CPII, a small chlorophyll (Chl)a/b antenna complex the fluorescence lifetime of which has been reported to be independent of excitation intensity over a wide intensity range of picosecond pulses. We have modeled the kinetics from the point of view that Chla molecules in CPII are Förster coupled so that a second excitation received by the group of Chla's either creates a state with two localized excitons or raises the first one to a doubly excited state. The data on CPII can be understood on the basis of a kinetic model that does not exclude exciton annihilation during the excitation pulse. The implied annihilation rate is consistent with our theoretical estimates of that rate obtained by applying excitation transfer theory to pairs of molecules both initially excited.

A femtosecond visible/visible and visible/mid-infrared transient absorption study of the light harvesting complex II

Light harvesting complex II (LHCII) is the most abundant protein in the thylakoid membrane of higher plants and green algae. LHCII acts to collect solar radiation, transferring this energy mainly toward photosystem II, with a smaller amount going to photosystem I; it is then converted into a chemical, storable form. We performed time-resolved femtosecond visible pump/mid-infrared probe and visible pump/visible probe absorption difference spectroscopy on purified LHCII to gain insight into the energy transfer in this complex occurring in the femto-picosecond time regime. We find that information derived from mid-infrared spectra, together with structural and modeling information, provides a unique visualization of the flow of energy via the bottleneck pigment chlorophyll a604.

Protein-pigments and the photosystem II reaction center: a glimpse into the history of research and reminiscences

This article provides a glimpse into the dawning of research on chlorophyll-protein complexes and a brief recollection of the path that led us to the identification of the photosystem II reaction center, i.e., the polypeptides that carry the site of primary charge separation in oxygenic photosynthesis. A preliminary version of the personal review on the latter topic has already appeared in this journal (Satoh Photosynth Res 76:233-240, 2003).

Chlorophyll fluorescence emission spectrum inside a leaf

Chlorophyll a fluorescence can be used as an early stress indicator. Fluorescence is also connected to photosynthesis so it can be proposed for global monitoring of vegetation status from a satellite platform. Nevertheless, the correct interpretation of fluorescence requires accurate physical models. The spectral shape of the leaf fluorescence free of any re-absorption effect plays a key role in the models and is difficult to measure. We present a vegetation fluorescence emission spectrum free of re-absorption based on a combination of measurements and modelling. The suggested spectrum takes into account the photosystem I and II spectra and their relative contribution to fluorescence. This emission spectrum is applicable to describe vegetation fluorescence in biospectroscopy and remote sensing.

The mystery of oxygen evolution: analysis of structure and function of photosystem II, the water-plastoquinone oxido-reductase

Photosystem II (PS II) of thylakoid membrane of photosynthetic organisms has drawn attention of researchers over the years because it is the only system on Earth that provides us with oxygen that we breathe. In the recent past, structure of PS II has been the focus of research in plant science. The report of X-ray crystallographic structure of PS II complex by the research groups of James Barber and So Iwata in UK is a milestone in the area of research in photosynthesis. It follows the pioneering and elegant work from the laboratories of Horst Witt and W. Saenger in Germany, and J. Shen in Japan. It is time to analyze the historic events during the long journey made by the researchers to arrive at this point. This review makes an attempt to critically review the growth of the advancement of concepts and knowledge on the photosystem in the background of technological development. We conclude the review with perspectives on research and technology that should reveal the complete story of PS II of thylakoid in the future.

Dynamics of the history of photosynthesis research

A personal view of the history of progress in photosynthesis research beginning in the seventeenth century and ending in 1992 is presented in a chart form. The 350-year time span is divided arbitrarily into seven periods by the "development junctures", which are likened to bamboo joints. The tempo of progress is reflected in the duration of the periods, starting from over 200 years for Period I, which progressively shortens in subsequent periods. This brief introduction highlights some of the events to show the dynamic nature of the progress in photosynthesis research.

The chlorophyll-protein complexes of higher plant photosynthetic membranes or Just what green band is that?

Higher plant thylakoid membranes can be fractionated into a bewildering array of macrocomplexes, chlorophyll-protein complexes and chlorophyll-proteins with various deteregents and separations techniques. The chemical nature of each of these entities depends on the particular methods used to obtain them. This review summarizes the current status of the biochemical identification and characterization of individual chlorophyll-proteins and chlorophyll-protein complexes, and attempts to clarify the relationships among them.

Sequence of two genes in pea chloroplast DNA coding for 84 and 82 kD polypeptides of the photosystem I complex

The genes encoding the two P700 chlorophyll a-apoproteins of the photosystem I complex were localized on the pea (Pisum sativum) chloroplast genome. The nucleotide sequence of the genes and the flanking regions has been determined. The genes are separated by 25 bp and are probably cotranscribed. The 5' terminal gene (psaA1) codes for a 761-residue protein (MW 84.1 kD) and the 3' terminal gene (psaA2) for a 734-residue protein (MW 82.4 kD). Both proteins are highly hydrophobic and contain eleven putative membrane-spanning domains. The homology to the corresponding polypeptides from maize are 89% and 95% for psaA1 and psaA2, respectively. A putative promoter has been identified for the psaA1 gene, and potential ribosome binding sites are present before both genes.

Chlorophyll-protein complexes

Recent advances in the studies on chlorophyll-protein complexes of higher plants are summarized in this article. Special emphasis is laid on the isolation, pigment composition and the absorption and fluorescence properties of the complexes.

Organization of the photosynthetic units, and onset of electron transport and excitation energy distribution in greening leaves

The development and organization of the Photosynthetic units follow a step-wise assembly process. First the core complexes of the PSI and PSII units are formed, followed by their light-harvesting components; then an assembly process of these components into supramolecular structures takes place. Parallel to this, the control of excitation energy distribution between the two photosystems is established. This control is attributed to the modulation of the PSI unit effective cross section, which is possible only when LHC-I is formed and assembled into CPIa. Parallel to the formation of PSI and PSII, the electron carriers are synthesized and the electron transport chain is assembled. The number of PSII units operating per electron transport chain remains constant throughout development and equal to that of the mature chloroplast, but the number of PSI units per chain varies with PSII unit size. During development, when the rate of Chla synthesis is low, relative to the other thylakoid components, or is completely stopped, then the newly formed or preexisting LHC-I and LHC-II proteins are digested and their Chla is used for the formation of PS core complexes.

Partial characterization of a minor chlorophyll-protein found in primary thylakoids of intermittently illuminated maize

A mild solubilization with sodium dodecyl sulphate of intermittently illuminated maize (Zea mays L. Mvsc 429) thylakoids allows the separation of a minor chlorophyll-protein in the position of the light harvesting chlorophyll-protein monomer of green plants by polyacrylamide gel electrophoresis. It contains mainly chlorophyll a, its chlorophyll b content may come from the slightly contaminating light harvesting chlorophyll a/b-protein. It represents about 15% of the chlorophyll in protochloroplasts. The new chlorophyll-protein has an absorption maximum at 672 nm, and only one fluorescence emission peak at 680 nm. A 34 kD polypeptide is the most abundant one in the polypeptide pattern of the complex. The function of the new chlorophyll-protein is unknown at present. Its relationship to other chlorophyll-proteins is discussed.

Isolation of chlorophyll-protein complexes and quantification of electron transport components in Synura petersenii and Tribonema aequale

The chlorophyll-protein complexes of the yellow alga Synura petersenii (Chrysophyceae) and the yellow-green alga Tribonema aequale (Xanthophyceae) were studied. The sodiumdodecylsulfate/sodiumdesoxycholate solubilized photosynthetic membranes of these species yielded three distinct pigment-protein complexes and a non-proteinuous zone of free pigments, when subjected to SDS polyacrylamid gel electrophoresis. The slowest migrating protein was identical to complex I (CP I), the P-700 chlorophyll a-protein, which possessed 60 chlorophyll a molecules per reaction center in Tribonema and 108 in Synura. The zone of intermediate mobility contained chlorophyll a and carotenoids. The absorption spectrum of this complex was very similar to the chlorophyll a-protein of photosystem II (CP a), which is known from green plants. The fastest migrating pigment protein zone was identified as a light-harvesting chlorophyll-protein complex. In Synura this protein was characterized by the content of chlorophyll c and of fucoxanthin. Therefore this complex will be named as LH Chl a/c-fucocanthin protein. In addition to the separation of the chlorophyll-protein complexes the cellular contents of P-700, cytochrome f (bound cytochrome) and cytochrome c-553 (soluble cytochrome) were measured. The stoichiometry of cytochrome f: cytochrome c-553:P-700 was found to be 1:4:2.4 in Tribonema and 1:6:3.4 in Synurá.

Two chlorophyll-binding subunits of the photosystem 2 reaction center complex isolated from the thermophilic cyanobacterium Synechococcus sp

The reaction center of photosystem 2 has been highly purified from digitonin-solubilized thylakoid membranes of the thermophilic cyanobacterium Synechococcus sp. by means of sucrose density gradient centrifugation and electrophoresis on polyacrylamide gels containing digitonin. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of isolated reaction center complex yielded four chlorophyll a proteins named CP2-a, CP2-b, CP2-c, and CP2-d. When reelectrophoresed, CP2-a was transformed to CP2-d, and CP2-b was converted to CP2-a and CP2-d. The reaction center complex consisted of two major polypeptides of 47,000 and 40,000 Da and several minor polypeptides. CP2-b contained a 47,000-Da polypeptide together with 66,000- and 31,000-Da polypeptides, while CP2-a and CP2-d had only a 47,000-Da polypeptide. The apoprotein of CP2-c was a 40,000-Da polypeptide. Absorption spectra of CP2-a, -b, and -d were similar to each other but distinctly different from those of CP2-c at liquid nitrogen temperature. The reaction center complex showed two fluorescence emission bands at 686 and 694 nm at 77 degrees K. CP2-a, -b, and -d emitted the band at 694 nm, whereas the fluorescence peak at 686 nm was associated with CP2-c. It is concluded that the photosystem 2 reaction center complex contains two chlorophyll-binding subunits, CP2-d (or CP2-a) which may be the site of the primary photochemistry of photosystem 2 and CP2-c which may function as the antenna of the reaction center of photosystem 2.

Regulation of photosynthesis by reversible phosphorylation of the light-harvesting chlorophyll a/b protein

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Isolation of chlorophyll-protein complexes and quantification of electron transport components in Synura petersenil and Tribonema aequale

The chlorophyll-protein complexes of the yellow alga Synura petersenii (Chrysophyceae) and the yellow-green alga Tribonema aequale (Xanthophyceae) were studied. The sodiumdodecylsulfate/sodiumdesoxycholate solubilized photosynthetic membranes of these species yielded three distinct pigment-protein complexes and a non-proteinous zone of free pigments, when subjected to SDS polyacrylamid gel electrophoresis. The slowest migrating protein was identical to complex I (CP I), the P-700 chlorophyll a-protein, which possessed 60 chlorophyll a molecules per reaction center in Tribonema and 108 in Synura. The zone of intermediate mobility contained chlorophyll a and carotenoids. The absorption spectrum of this complex was very similar to the chlorophyll a-protein of photosystem II (CP a), which is known from green plants. The fastest migrating pigment protein zone was identified as a light-harvesting chlorophyll-protein complex. In Synura this protein was characterized by the content of chlorophyll c and of fucoxanthin. Therefore this complex will be named as LH Chl a/c-fucocanthin protein. In addition to the separation of the chlorophyll-protein complexes the cellular contents of P-700, cytochrome f (bound cytochrome) and cytochrome c-553 (soluble cytochrome) were measured. The stoichiometry of cytochrome f: cytochrome c-553:P-700 was found to be 1:4:2.4 in Tribonema and 1:6:3.4 in Synurá.

P-700 content and polypeptide profile of chlorophyll-protein complexes of spinach and barley thylakoids

Of the six chlorophyll-protein complexes of spinach and barley resolved by mild gel electrophoresis, two were chlorophyll a-protein complexes of PS I, namely CP1a and CP1, which accounted for up to 30% of the total chlorophyll. Both of these complexes had one P-700 per 120 chlorophyll a molecules. Since spinach and barley thylakoids have some 400 chlorophyll molecules per P-700, these complexes may not have lost any of the chlorophyll associated with them in vivo. This may account for CP1a and CP1 having the characteristic low-temperature fluorescence normally associated with PS I in vivo, which is not found in complexes with low chlorophyll/P-700 ratios. Two-dimensional electrophoresis showed that all of the chlorophyll a and P-700 of CP1 was bound to 70 kilodalton polypeptides. The PS I reaction centre complex of lowest mobility, CP1a, contained CP1 and four additional low molecular weight polypeptides. The three light-harvesting complexes resolved had major 25 and 23 kilodalton polypeptides. The presumed reaction centre complex of PS II contained major 50 and 47 kilodalton polypeptides.

Analysis of light-controlled accumulation of carotenoids in mustard (Sinapis alba L.) seedlings

Carotenoid accumulation in the cotyledons of the mustard seedling (Sinapis alba L.) is controlled by light. Besides the stimulatory function of phytochrome in carotenogenesis the experiments reveal the significance of chlorophyll accumulation for the accumulation of larger amounts of acrotenoids. A specific blue light effect was not found. The data suggest that light exerts its control over carotenoid biogenesis through two separate mechanisms: A phytochrome regulation of enzyme levels before a postulated pool of free carotenoids, and a regulation by chlorophyll draining the pool by complex-formation.

Purification and characterization of 33 kilodalton protein of spinach chloroplasts

A protein was prepared from spinach chloroplasts in a highly purified form. The isoelectric point of the protein was 5.2. The apparent molecular weight was estimated to be 33 000 by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate and urea, and 34 000 by gel filtration column chromatography with Sephadex G-100. The protein was provisionally named '33 kilodalton protein' according to the molecular weight. The absorption spectrum of the protein did not show any absorption band in the visible region. No histidine was found in the amino acid analysis of the protein. The 33 kilodalton protein was released from the thylakoid membrane by EDTA-treatment and also by sonic oscillation. The protein was bound to System II particles, but not to System I particles.

Evidence for a structural role for chlorophyll in chlorophyll-protein complexes

1. Chymotrypsin treatment of spinach chloroplast membranes does not change the electrophoretic mobility of either chlorophyll-protein complex 1 or 2. 2. The extraction of lipids with 80% acetone after treatment of the membranes with chymotrypsin reveals that the polypeptide components of both chlorophyll-protein complexes had been extensively digested. The extraction of carotenes with petroleum ether under the same conditions does not change the electrophoretic mobility of the chlorophyll-protein complexes. 3. Fluorescence polarisation studies of chlorophyll-protein complex 2 reveal that the chymotrypsin digestion of this complex does not result in changes of mutual orientation or distance apart of chlorophyll a, chlorophyll b or carotenoid. 4. Two polypeptide components have been detected after lipid extraction of electrophoretically purified chlorophyll-protein complexes 1 and 2. The SDS molecular weights are 24 000 and 27 000 for complex 2, and 68 000 and 64 000 for complex 1. 5. We conclude that chlorophyll performs an important structural function in both chlorophyll-protein complexes.

Resolution of the light-harvesting chlorophyll a/b-protein of vicia faba chloroplasts into two different chlorophyll-protein complexes

Thylakoids of Vicia faba chloroplasts disaggregated by sodium dodecyl sulfate were separated by means of different electrophoretic systems. Under the conditions of a high resolving gel system the chlorophyll containing zone previously termed chlorophyll-protein complex II or light-harvesting chlorophyll a/b-protein was found to be inhomogeneous. It represents a mixture of two distinct chlorophyll-proteins characterized by different spectral properties and different apoproteins. One chlorophyll-protein exhibits a chlorophyll a/b ratio of 0.9 and is associated with polypetides of 24,000 and 23,000 daltons. The 24,000 dalton band is proved to bind chlorophyll and has a light-harvesting function. The function of the 23,000 dalton band is unknown. The second chlorophyll-protein has a chlorophyll a/b ratio of 2.1 and an additional absorption maximum in the position of 637 nm. It is associated with only one polypeptide which has an apparent molecular weight of 23,000. The two 23,000 dalton polypeptides occurring in both complexes are not identical.