COMPUTER SIMULATION OF EXCITON JUMPING STATISTICS AND ENERGY FLOW IN C‐PHYCOCYANIN OF ALGAE <i>Agmenellum quadruplicatum</i> IN THE PRESENCE OF TRAPS

Demidov, A.M.; Borisov, A. Yu.

doi:10.1111/j.1751-1097.1994.tb03941.x

Cited by 3 publications

(3 citation statements)

References 30 publications

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“…Using the data presented above and Eq. A2.1, we calculate t1 = 21.3 ps, t2 = 47 ps, and t3 = 1500 ps (Demidov and Borisov, 1994c). These values match well the theoretical evaluations by Sauer et al (1988): 21 ps, 45 ps, and 1500 ps; experimental data (Tf-r = 46 ps) by Holzwarth et al (1987); and Monte-Carlo simulation (rTfa,t 33-48 ps) by Demidov and Borisov (1993).…”

Section: Excitationsupporting

confidence: 84%

“…In particular, it is obvious that the absorption anisotropy (investigated by both groups) should depend on the excitation distribution over the monomer chromophores, and as soon as quasi-equilibrium is established (t < 1 ns), the anisotropy should be stable. Sauer et al (1988) and Demidov and Borisov (1994c) have calculated that there are two characteristic timescales for excitation equilibration in C-PC monomers: ti = 21 ps and t2 = 47 ps. Thus, at times greater than 100 ps the value of the absorption anisotropy should be stable.…”

Section: Application To C-phycocyanin Aggregatesmentioning

confidence: 99%

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Quantitative calculations of fluorescence polarization and absorption anisotropy kinetics of double- and triple-chromophore complexes with energy transfer

Demidov

1994

Biophysical Journal

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A new method is presented for calculation of the fluorescence depolarization and kinetics of absorption anisotropy for molecular complexes with a limited number of chromophores. The method considers absorption and emission of light by both chromophores, and also energy transfer between them, with regard to their mutual orientations. The chromophores in each individual complex are rigidly positioned. The complexes are randomly distributed and oriented in space, and there is no energy transfer between them. The new "practical" formula for absorption anisotropy and fluorescence depolarization kinetics, P(t) = [3B(t) - 1 + 2A(t)]/[3 + B(t) + 4A(t)], is derived both for double- and triple-chromophore complexes with delta-pulse excitation. The parameter B(t) is given by (a) B(t) = cos2(theta) for double-chromophore complexes, and (b) B(t) = q12(t)cos2(theta 12) + q13(t)-cos2(theta 13) + q23(t)cos2(theta 23) for triple-chromophore complexes, where q12(t) + q13(t) + q23(t) = 1. Here theta ij are the angles between the chromophore transition dipole moments in the individual molecular complex. The parameters qij(t) and A(t) are dependent on chromophore spectroscopic features and on the rates of energy transfer.

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Section: Excitationsupporting

confidence: 84%

Section: Application To C-phycocyanin Aggregatesmentioning

confidence: 99%

Quantitative calculations of fluorescence polarization and absorption anisotropy kinetics of double- and triple-chromophore complexes with energy transfer

Demidov

1994

Biophysical Journal

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“…1) is equally distributed among them. Thus, the original system of nine equations can be reduced to a system of three (29):…”

Section: Methodsmentioning

confidence: 99%

Determination of Fluorescence Polarization and Absorption Anisotropy in Molecular Complexes Having Threefold Rotational Symmetry

Demidov

Andrews

1996

Photochem & Photobiology

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The current work concerns investigation of the polarization properties of complex molecular ensembles exhibiting threefold (C,) rotational symmetry, particularly with regard to the interplay between their structure and dynamics of internal energy transfer. We assume that the molecules or chromophores in such complexes possess strongly overlapped spectra both for absorption and fluorescence. Such trimeric structures are widely found in biological preparations, as for example the trimer of Cphycocyanin (C-PC). Higher order aggregates, e.g. hexamers and three-hexamer rods, are also investigated and compared with the trimer case. The theory addresses both steady-state and 6-pulse excitation and establishes some links between them. Monochromophoric, bichromophoric and trichromophoric molecular complexes are individually examined.For steady-state excitation, analytical formulas are reported for the degree of fluorescence polarization and absorption anisotropy. It is shown that the polarization is dependent on the chromophore inclination relative to the symmetry axis, the relative efficiencies of absorption and fluorescence by chromophores of different spectral types, and the rates of energy equilibration. To assess the validity of the theory, it has been applied to C-PC aggregates. Here it was found that different C-PC aggregates provide practically identical polarization response. For S-pulse excitation we give analytical formulas for determination of the fluorescence depolarization, and also the depolarization associated with absorption recovery, both for a monochromophoric trimer and some particular cases of bichromophoric trimer. More complicated systems are analyzed by computer modeling. Thus it transpires that the initial polarization anisotropy r(t = 0) takes the value 0.4 for all considered aggregates; the long-time limit r(t -+ m) has about the same value as is associated with steady-state excitation. We also show that with steady-state excitation the degree of fluorescence polarization is practically equal for various C, aggregates of C-PC, and that the major factor determining the polarization is the chromophore orientation relative to the symmetry axis.

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Cyanobacterial Phycobilisomes

MacColl

1998

Journal of Structural Biology

581

442

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Cyanobacterial phycobilisomes harvest light and cause energy migration usually toward photosystem II reaction centers. Energy transfer from phycobilisomes directly to photosystem I may occur under certain light conditions. The phycobilisomes are highly organized complexes of various biliproteins and linker polypeptides. Phycobilisomes are composed of rods and a core. The biliproteins have their bilins (chromophores) arranged to produce rapid and directional energy migration through the phycobilisomes and to chlorophyll a in the thylakoid membrane. The modulation of the energy levels of the four chemically different bilins by a variety of influences produces more efficient light harvesting and energy migration. Acclimation of cyanobacterial phycobilisomes to growth light by complementary chromatic adaptation is a complex process that changes the ratio of phycocyanin to phycoerythrin in rods of certain phycobilisomes to improve light harvesting in changing habitats. The linkers govern the assembly of the biliproteins into phycobilisomes, and, even if colorless, in certain cases they have been shown to improve the energy migration process. The Lcm polypeptide has several functions, including the linker function of determining the organization of the phycobilisome cores. Details of how linkers perform their tasks are still topics of interest. The transfer of excitation energy from bilin to bilin is considered, particularly for monomers and trimers of C-phycocyanin, phycoerythrocyanin, and allophycocyanin. Phycobilisomes are one of the ways cyanobacteria thrive in varying and sometimes extreme habitats. Various biliprotein properties perhaps not related to photosynthesis are considered: the photoreversibility of phycoviolobilin, biophysical studies, and biliproteins in evolution. Copyright 1998 Academic Press.

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COMPUTER SIMULATION OF EXCITON JUMPING STATISTICS AND ENERGY FLOW IN C‐PHYCOCYANIN OF ALGAE Agmenellum quadruplicatum IN THE PRESENCE OF TRAPS

Cited by 3 publications

References 30 publications

Quantitative calculations of fluorescence polarization and absorption anisotropy kinetics of double- and triple-chromophore complexes with energy transfer

Quantitative calculations of fluorescence polarization and absorption anisotropy kinetics of double- and triple-chromophore complexes with energy transfer

Determination of Fluorescence Polarization and Absorption Anisotropy in Molecular Complexes Having Threefold Rotational Symmetry

Cyanobacterial Phycobilisomes

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