Exciton interactions of chlorophyll tetramer in water-soluble chlorophyll-binding protein BoWSCP.

The exciton interaction of four chlorophyll a (Chl a) molecules in a symmetrical tetrameric complex of the water-soluble chlorophyll-binding protein BoWSCP was analyzed in the pH range of 3-11. Exciton splitting ΔE = 232 ± 2 cm of the Q band of Chl a into two subcomponents with relative intensities of 78.1 ± 0.

Femtosecond Dynamics of Excited States of Chlorophyll Tetramer in Water-Soluble Chlorophyll-Binding Protein BoWSCP.

The paper reports on the absorption dynamics of chlorophyll a in a symmetric tetrameric complex of the water-soluble chlorophyll-binding protein BoWSCP. It was measured by a broadband femtosecond laser pump-probe spectroscopy within the range from 400 to 750 nm and with a time resolution of 20 fs-200 ps. When BoWSCP was excited in the region of the Soret band at a wavelength of 430 nm, nonradiative intramolecular conversion S→S was observed with a characteristic time of 83 ± 9 fs.

Chlorophyll a Dimers Bound in the Water-Soluble Protein BoWSCP Photosensitize the Reduction of Cytochrome c.

When bound to water-soluble proteins of the WSCP family, chlorophyll molecules form dimers structurally similar to the "special pair" of chlorophylls (bacteriochlorophylls) in photosynthetic reaction centers. Being exposed to red light (λ ≥ 650 nm) in oxygen-free solutions, chlorophyll a dimers harbored by BoWSCP holoproteins (from Brassica oleracea var. botrytis) have sensitized the reduction of cytochrome c.

[Water Soluble Chlorophyll-Binding Proteins of Plants: Structure, Properties and Functions].

Water soluble chlorophyll-binding proteins (WSCPs) of higher plants differ from most proteins containing chlorophyll orbacteriochlorophyll in that they are soluble in watr and are neither embedded in the lipid membrane nor directly involved in the process of photosynthesis. Chlorophyll molecules in WSCPs ensembles are packed in dimers within the hydrophobic zone of the protein matrix, similar to the structure of a chlorophyll "special pair" in the reaction centers of phototrophs. This fact together with the detected photosensitizing activity of WSCPs makes it possible to consider these proteins as a promising object for modelling the evolutionary prototypes of the photosynthetic apparatus, as well as for developing the artificial solar energy converters.

Non-photochemical quenching in the cells of the carotenogenic chlorophyte Haematococcus lacustris under favorable conditions and under stress.

The microalga Haematococcus lacustris (formerly H. pluvialis) is the richest source of the valuable pigment astaxanthin, accumulated in red aplanospores (haematocysts). In this work, we report on the photoprotective mechanisms in H.

Carotenogenic response in photosynthetic organisms: a colorful story.

Carotenoids are a diverse group of terpenoid pigments ubiquitous in and essential for functioning of phototrophs. Most of the researchers in the field are focused on the primary carotenoids serving light harvesting, photoprotection, and supporting the structural integrity of the photosynthetic apparatus (PSA) within the thylakoid membranes. A distinct group of the pigments functionally and structurally uncoupled from the PSA and accumulating outside of the thylakoids is called secondary carotenoids.

Characterization of the low-temperature triplet state of chlorophyll in photosystem II core complexes: Application of phosphorescence measurements and Fourier transform infrared spectroscopy.

Phosphorescence measurements at 77 K and light-induced FTIR difference spectroscopy at 95 K were applied to study of the triplet state of chlorophyll a ((3)Chl) in photosystem II (PSII) core complexes isolated from spinach. Using both methods, (3)Chl was observed in the core preparations with doubly reduced primary quinone acceptor QA. The spectral parameters of Chl phosphorescence resemble those in the isolated PSII reaction centers (RCs).

Low-temperature (77 K) phosphorescence of triplet chlorophyll in isolated reaction centers of photosystem II.

Phosphorescence characterized by the main emission band at 952 ± 1 nm (1.30 eV), the lifetime of 1.5 ± 0.

Phosphorescence study of chlorophyll d photophysics. Determination of the energy and lifetime of the photo-excited triplet state. Evidence of singlet oxygen photosensitization.

Chlorophyll d (Chl d) is the major pigment in both photosystems (PSI and II) of the cyanobacterium Acaryochloris marina, whose pigment composition represents an interesting alternative in oxygenic photosynthesis. While abundant information is available relative to photophysical properties of Chl a , the understanding of Chl d photophysics is still incomplete. In this paper, we present for the first time a characterization of Chl d phosphorescence, which accompanies radiative deactivation of the photoexcited triplet state of this pigment.

[Mechanism of photosensitized luminescence of singlet oxygen dimols in air-saturated pigment solutions].

Luminescence of singlet oxygen dimols (1O2)2 with the main spectral maximum at 703-706 nm and much weaker bands at 640 and 770-780 nm was studied using mechanical phosphoroscopes in aerobic solutions of the nonfluorescent photosensitizer phenalenone in CCl4 and C6F6 at relatively low radiant power. The spectrum of this luminescence resembles that of dimol luminescence, which we had detected previously in solutions of porphyrins and other compounds. It was shown that, in phenalenone solutions, the mechanism of dimol luminescence involves reaction of two 1O2 molecules and one ground-state pigment molecule.

[Phosphorescence analysis of the chlorophyll triplet state in preparations of photosystem II].

The low-temperature (77 K) phosphorescence of chlorophyll (Chl) in the reaction centres (D1D2-cyt b559-particles) and the core complexes of photosystem II isolated from higher plants was studied. Two phosphorescence spectral bands with the emission maxima at 950 and 977 nm, excitation maxima at 666 and 675-680 nm, and the lifetimes equal to 2 and 1.5 ms, respectively, were registered.

Involvement of uncoupled antenna chlorophylls in photoinhibition in thylakoids.

Evidence is presented, by means of both fluorescence and action spectroscopy, that a small, spectroscopically heterogeneous population of both Chl a and Chl b molecules is present in isolated spinach thylakoids and is active in photoinhibition. The broadness of the action spectrum suggests that degraded or incompletely assembled pigment-protein complexes may be involved.

Photoelectric responses of oxygen-evolving complexes of photosystem II.

The generation of a transmembrane electric potential difference induced by a series of laser flashes was studied by the direct electrometrical method in proteoliposomes containing oxygen-evolving particles of photosystem II. In addition to the fast stage of generation of the membrane potential, which is due to electron transfer from the redox active tyrosine residue Tyr-161 (YZ) to the primary quinone acceptor QA, electrogenic stages corresponding to the S1 --> S2 (tau = 30 &mgr;sec), S2 --> S3 (tau = 240 &mgr;sec), and S3 --> S4 --> S0 (tau = 6.2 msec) transitions of the oxygen-evolving complex (OEC) were observed.

Photophysical studies of pheophorbide a and pheophytin a. Phosphorescence and photosensitized singlet oxygen luminescence.

The triplet states of pheophorbide a and pheophytin a were studied in several environments by direct measurement of the phosphorescence of the pigments and photosensitized singlet oxygen (1O2) luminescence. The spectra, lifetimes and quantum yields of phosphorescence and the quantum yields of 1O2 generation were determined. These parameters are similar for monomeric molecules of both pigments in all the environments studied.

[Sensibilized dimer luminescence of singlet molecular oxygen in solutions].

With the use of mechanical phosphoroscope the "universal" delayed emission has been found in aerobic solutions of different sensitizers in CCl4. The spectrum of this emission has the main maximum at 703 nm. The luminescence intensity is proportional to the square of the intensity of the exciting light.