Search results for "Complex."
showing 10 items of 5824 documents
Excitonic Energy Level Structure and Pigment−Protein Interactions in the Recombinant Water-Soluble Chlorophyll Protein. I. Difference Fluorescence Li…
2011
Difference fluorescence line-narrowing spectroscopy at 4.5 K was employed to investigate electron-phonon and electron-vibrational coupling strengths of the lower exciton level of water-soluble chlorophyll-binding protein (WSCP) from cauliflower reconstituted with chlorophyll a or chlorophyll b, respectively. The electron-phonon coupling is found to be moderate with integral Huang-Rhys factors S in the order of 0.81-0.85. A weak dependence of S on excitation wavelength within the inhomogeneously broadened fluorescence origin band is attributed to a sizable contribution of nonresonant excitation that varies with excitation wavelength. The strongly asymmetric and highly structured one-phonon p…
Pigment Binding, Fluorescence Properties, and Oligomerization Behavior of Lhca5, a Novel Light-harvesting Protein
2005
A new potential light-harvesting protein, named Lhca5, was recently detected in higher plants. Because of the low amount of Lhca5 in thylakoid membranes, the isolation of a native Lhca5 pigment-protein complex has not been achieved to date. Therefore, we used in vitro reconstitution to analyze whether Lhca5 binds pigments and is actually an additional light-harvesting protein. By this approach we could demonstrate that Lhca5 binds pigments in a unique stoichiometry. Analyses of pigment requirements for light-harvesting complex formation by Lhca5 revealed that chlorophyll b is the only indispensable pigment. Fluorescence measurements showed that ligated chlorophylls and carotenoids are arran…
Decreasing the chlorophyll a/b ratio in reconstituted LHCII: Structural and functional consequences
1999
Trimeric (bT) and monomeric (bM) light-harvesting complex II (LHCII) with a chlorophyll a/b ratio of 0.03 were reconstituted from the apoprotein overexpressed in Escherichia coli. Chlorophyll/xanthophyll and chlorophyll/protein ratios of bT complexes and 'native' LHCII are rather similar, namely, 0.28 vs 0. 27 and 10.5 +/- 1.5 vs 12, respectively, indicating the replacement of most chlorophyll a molecules with chlorophyll b, leaving one chlorophyll a per trimeric complex. The LD spectrum of the bT complexes strongly suggests that the chlorophyll b molecules adopt orientations similar to those of the chlorophylls a that they replace. The circular dichroism (CD) spectra of bM and bT complexes…
Exchange of Pigment-Binding Amino Acids in Light-Harvesting Chlorophyll a/b Protein
1999
Four amino acids in the major light-harvesting chlorophyll (Chl) a/b complex (LHCII) that are thought to coordinate Chl molecules have been exchanged with amino acids that presumably cannot bind Chl. Amino acids H68, Q131, Q197, and H212 are positioned in helixes B, C, A, and D, respectively, and, according to the LHCII crystal structure [Kühlbrandt, W., et al. (1994) Nature 367, 614-621], coordinate the Chl molecules named a(5), b(6), a(3), and b(3). Moreover, a double mutant was analyzed carrying exchanges at positions E65 and H68, presumably affecting Chls a(4) and a(5). All mutant proteins could be reconstituted in vitro with pigments, although the thermal stability of the resulting mut…
Inactivation of a plastid evolutionary conserved gene affects PSII electron transport, life span and fitness of tobacco plants
2007
Chloroplasts contain a plastoquinone-NADH-oxidoreductase (Ndh) complex involved in protection against stress and the maintenance of cyclic electron flow. Inactivation of the Ndh complex delays the development of leaf senescence symptoms. Chlorophyll a fluorescence measurements, blue native gel electrophoresis, immunodetection and other techniques were employed to study tobacco (Nicotiana tabacum) Ndh-defective mutants (DeltandhF). The DeltandhF mutants compared with wild-type plants presented: (i) higher photosystem II : photosystem I (PSII : PSI) ratios; (ii) similar or higher levels of ascorbate, carotenoids, thylakoid peroxidase and superoxide dismutase, yield (Phi(PSII)) and maximal pho…
The negatively charged amino acids in the lumenal loop influence the pigment binding and conformation of the major light-harvesting chlorophyll a/b c…
2008
AbstractThe major chlorophyll (Chl) a/b complexes of photosystem II (LHCIIb), in addition to their primary light-harvesting function, play key roles in the organization of the granal ultrastructure of the thylakoid membranes and in various regulatory processes. These functions depend on the structural stability and flexibility of the complexes. The lumenal side of LHCIIb is exposed to broadly variable pH environments, due to the build-up and decay of the pH gradient during photosynthesis. Therefore, the negatively charged amino acids in the lumenal loop might be of paramount importance for adjusting the structure and functions of LHCIIb. In order to clarify the structural roles of these res…
Cadmium accumulation and buffering of cadmium-induced stress by arbuscular mycorrhiza in three Pisum sativum L. genotypes
2002
The role of arbuscular mycorrhiza in reducing Cd stress was investigated in three genotypes of Pisum sativum L. (cv. Frisson, VIR4788, VIR7128), grown in soil/sand pot cultures in the presence and absence of 2-3 mg kg(-1) bioavailable Cd, and inoculated or not with the arbuscular mycorrhizal fungus Glomus intraradices. Shoot, root and pod biomass were decreased by Cd in non-mycorrhizal plants. The presence of mycorrhiza attenuated the negative effect of Cd so that shoot biomass and activity of photosystem II, based on chlorophyll a fluorescence, were not significantly different between mycorrhizal plants growing in the presence or absence of the heavy metal (HM). Total P concentrations were…
A battery of toxicity tests as indicators of decontamination in composting oily waste.
2000
Heterogeneous oily waste from an old dumping site was composted in three windrows constructed from different proportions of waste, sewage sludge, and bark. The objectives of this pilot study were to examine the usefulness of composting as a treatment method for this particular waste and to study decontamination in the composting process by using a battery of toxicity tests. Five samples from the windrow having intermediate oil concentrations were tested with toxicity tests based on microbes (Pseudomonas putida growth inhibition test, ToxiChromotest, MetPLATE, and three different modifications of a luminescent bacterial test), enzyme inhibition (reverse electron transport), plants (duckweed …
Filling the “green gap” of the major light-harvesting chlorophyll a/b complex by covalent attachment of Rhodamine Red
2009
AbstractThe major light-harvesting chlorophyll a/b complex (LHCII) greatly enhances the efficiency of photosynthesis in green plants. Recombinant LHCII can be assembled in vitro from its denatured, bacterially expressed apoprotein and plant pigments. This makes it an interesting candidate for biomimetic light-harvesting in photovoltaic applications. Due to its almost 20 pigments bound per apoprotein, LHCII absorbs efficiently in the blue and red spectral domains of visible light but less efficiently in the green domain, the so-called “green gap” in its absorption spectrum. Here we present a hybrid complex of recombinant LHCII with organic dyes that add to LHCII absorption in the green spect…
Carotenoid binding sites in LHCIIb
2000
The major light-harvesting complex of photosystem II can be reconstituted in vitro from its bacterially expressed apoprotein with chlorophylls a and b and neoxanthin, violaxanthin, lutein, or zeaxanthin as the only xanthophyll. Reconstitution of these one-carotenoid complexes requires low-stringency conditions during complex formation and isolation. Neoxanthin complexes (containing 30–50% of the all-trans isomer) disintegrate during electrophoresis, exhibit a largely reduced resistance against proteolytic attack; in addition, energy transfer from Chl b to Chl a is easily disrupted at elevated temperature. Complexes reconstituted in the presence of either zeaxanthin or lutein contain nearly …